Mercurial > octave-nkf
annotate doc/interpreter/func.txi @ 19628:fe689210525c gui-release
maint: Periodic merge of stable to gui-release.
| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Tue, 20 Jan 2015 10:05:42 -0500 |
| parents | 4cf930a64fad 446c46af4b42 |
| children | 0e1f5a750d00 |
| rev | line source |
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1 @c Copyright (C) 1996-2013 John W. Eaton |
| 7018 | 2 @c |
| 3 @c This file is part of Octave. | |
| 4 @c | |
| 5 @c Octave is free software; you can redistribute it and/or modify it | |
| 6 @c under the terms of the GNU General Public License as published by the | |
| 7 @c Free Software Foundation; either version 3 of the License, or (at | |
| 8 @c your option) any later version. | |
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9 @c |
| 7018 | 10 @c Octave is distributed in the hope that it will be useful, but WITHOUT |
| 11 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 @c for more details. | |
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14 @c |
| 7018 | 15 @c You should have received a copy of the GNU General Public License |
| 16 @c along with Octave; see the file COPYING. If not, see | |
| 17 @c <http://www.gnu.org/licenses/>. | |
| 3294 | 18 |
| 4167 | 19 @node Functions and Scripts |
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20 @chapter Functions and Scripts |
| 3294 | 21 @cindex defining functions |
| 22 @cindex user-defined functions | |
| 23 @cindex functions, user-defined | |
| 24 @cindex script files | |
| 25 | |
| 26 Complicated Octave programs can often be simplified by defining | |
| 27 functions. Functions can be defined directly on the command line during | |
| 28 interactive Octave sessions, or in external files, and can be called just | |
| 29 like built-in functions. | |
| 30 | |
| 31 @menu | |
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32 * Introduction to Function and Script Files:: |
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33 * Defining Functions:: |
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34 * Multiple Return Values:: |
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35 * Variable-length Argument Lists:: |
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36 * Ignoring Arguments:: |
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37 * Variable-length Return Lists:: |
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38 * Returning from a Function:: |
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39 * Default Arguments:: |
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40 * Function Files:: |
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41 * Script Files:: |
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42 * Function Handles Anonymous Functions Inline Functions:: |
| 6549 | 43 * Commands:: |
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44 * Organization of Functions:: |
| 3294 | 45 @end menu |
| 46 | |
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47 @node Introduction to Function and Script Files |
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48 @section Introduction to Function and Script Files |
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49 |
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50 There are seven different things covered in this section. |
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51 @enumerate |
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52 @item |
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53 Typing in a function at the command prompt. |
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54 |
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55 @item |
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56 Storing a group of commands in a file --- called a script file. |
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57 |
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58 @item |
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59 Storing a function in a file---called a function file. |
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60 |
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61 @item |
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62 Subfunctions in function files. |
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63 |
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64 @item |
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65 Multiple functions in one script file. |
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66 |
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67 @item |
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68 Private functions. |
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69 |
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70 @item |
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71 Nested functions. |
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72 @end enumerate |
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73 |
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74 Both function files and script files end with an extension of .m, for |
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75 @sc{matlab} compatibility. If you want more than one independent |
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76 functions in a file, it must be a script file (@pxref{Script Files}), |
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77 and to use these functions you must execute the script file before you |
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78 can use the functions that are in the script file. |
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79 |
| 4167 | 80 @node Defining Functions |
| 3294 | 81 @section Defining Functions |
| 82 @cindex @code{function} statement | |
| 83 @cindex @code{endfunction} statement | |
| 84 | |
| 85 In its simplest form, the definition of a function named @var{name} | |
| 86 looks like this: | |
| 87 | |
| 88 @example | |
| 89 @group | |
| 90 function @var{name} | |
| 91 @var{body} | |
| 92 endfunction | |
| 93 @end group | |
| 94 @end example | |
| 95 | |
| 96 @noindent | |
| 97 A valid function name is like a valid variable name: a sequence of | |
| 98 letters, digits and underscores, not starting with a digit. Functions | |
| 99 share the same pool of names as variables. | |
| 100 | |
| 101 The function @var{body} consists of Octave statements. It is the | |
| 102 most important part of the definition, because it says what the function | |
| 103 should actually @emph{do}. | |
| 104 | |
| 105 For example, here is a function that, when executed, will ring the bell | |
| 106 on your terminal (assuming that it is possible to do so): | |
| 107 | |
| 108 @example | |
| 109 @group | |
| 110 function wakeup | |
| 111 printf ("\a"); | |
| 112 endfunction | |
| 113 @end group | |
| 114 @end example | |
| 115 | |
| 116 The @code{printf} statement (@pxref{Input and Output}) simply tells | |
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117 Octave to print the string @qcode{"\a"}. The special character @samp{\a} |
| 3294 | 118 stands for the alert character (ASCII 7). @xref{Strings}. |
| 119 | |
| 120 Once this function is defined, you can ask Octave to evaluate it by | |
| 121 typing the name of the function. | |
| 122 | |
| 123 Normally, you will want to pass some information to the functions you | |
| 124 define. The syntax for passing parameters to a function in Octave is | |
| 125 | |
| 126 @example | |
| 127 @group | |
| 128 function @var{name} (@var{arg-list}) | |
| 129 @var{body} | |
| 130 endfunction | |
| 131 @end group | |
| 132 @end example | |
| 133 | |
| 134 @noindent | |
| 135 where @var{arg-list} is a comma-separated list of the function's | |
| 136 arguments. When the function is called, the argument names are used to | |
| 137 hold the argument values given in the call. The list of arguments may | |
| 138 be empty, in which case this form is equivalent to the one shown above. | |
| 139 | |
| 140 To print a message along with ringing the bell, you might modify the | |
| 6510 | 141 @code{wakeup} to look like this: |
| 3294 | 142 |
| 143 @example | |
| 144 @group | |
| 145 function wakeup (message) | |
| 146 printf ("\a%s\n", message); | |
| 147 endfunction | |
| 148 @end group | |
| 149 @end example | |
| 150 | |
| 151 Calling this function using a statement like this | |
| 152 | |
| 153 @example | |
| 154 wakeup ("Rise and shine!"); | |
| 155 @end example | |
| 156 | |
| 157 @noindent | |
| 158 will cause Octave to ring your terminal's bell and print the message | |
| 159 @samp{Rise and shine!}, followed by a newline character (the @samp{\n} | |
| 160 in the first argument to the @code{printf} statement). | |
| 161 | |
| 162 In most cases, you will also want to get some information back from the | |
| 163 functions you define. Here is the syntax for writing a function that | |
| 164 returns a single value: | |
| 165 | |
| 166 @example | |
| 167 @group | |
| 168 function @var{ret-var} = @var{name} (@var{arg-list}) | |
| 169 @var{body} | |
| 170 endfunction | |
| 171 @end group | |
| 172 @end example | |
| 173 | |
| 174 @noindent | |
| 175 The symbol @var{ret-var} is the name of the variable that will hold the | |
| 176 value to be returned by the function. This variable must be defined | |
| 177 before the end of the function body in order for the function to return | |
| 178 a value. | |
| 179 | |
| 180 Variables used in the body of a function are local to the | |
| 181 function. Variables named in @var{arg-list} and @var{ret-var} are also | |
| 182 local to the function. @xref{Global Variables}, for information about | |
| 183 how to access global variables inside a function. | |
| 184 | |
| 185 For example, here is a function that computes the average of the | |
| 186 elements of a vector: | |
| 187 | |
| 188 @example | |
| 189 @group | |
| 190 function retval = avg (v) | |
| 191 retval = sum (v) / length (v); | |
| 192 endfunction | |
| 193 @end group | |
| 194 @end example | |
| 195 | |
| 196 If we had written @code{avg} like this instead, | |
| 197 | |
| 198 @example | |
| 199 @group | |
| 200 function retval = avg (v) | |
| 4029 | 201 if (isvector (v)) |
| 3294 | 202 retval = sum (v) / length (v); |
| 203 endif | |
| 204 endfunction | |
| 205 @end group | |
| 206 @end example | |
| 207 | |
| 208 @noindent | |
| 209 and then called the function with a matrix instead of a vector as the | |
| 210 argument, Octave would have printed an error message like this: | |
| 211 | |
| 212 @example | |
| 213 @group | |
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214 error: value on right hand side of assignment is undefined |
| 3294 | 215 @end group |
| 216 @end example | |
| 217 | |
| 218 @noindent | |
| 219 because the body of the @code{if} statement was never executed, and | |
| 220 @code{retval} was never defined. To prevent obscure errors like this, | |
| 221 it is a good idea to always make sure that the return variables will | |
| 222 always have values, and to produce meaningful error messages when | |
| 223 problems are encountered. For example, @code{avg} could have been | |
| 224 written like this: | |
| 225 | |
| 226 @example | |
| 227 @group | |
| 228 function retval = avg (v) | |
| 229 retval = 0; | |
| 4029 | 230 if (isvector (v)) |
| 3294 | 231 retval = sum (v) / length (v); |
| 232 else | |
| 233 error ("avg: expecting vector argument"); | |
| 234 endif | |
| 235 endfunction | |
| 236 @end group | |
| 237 @end example | |
| 238 | |
| 239 There is still one additional problem with this function. What if it is | |
| 240 called without an argument? Without additional error checking, Octave | |
| 241 will probably print an error message that won't really help you track | |
| 242 down the source of the error. To allow you to catch errors like this, | |
| 243 Octave provides each function with an automatic variable called | |
| 244 @code{nargin}. Each time a function is called, @code{nargin} is | |
| 245 automatically initialized to the number of arguments that have actually | |
| 246 been passed to the function. For example, we might rewrite the | |
| 247 @code{avg} function like this: | |
| 248 | |
| 249 @example | |
| 250 @group | |
| 251 function retval = avg (v) | |
| 252 retval = 0; | |
| 253 if (nargin != 1) | |
| 254 usage ("avg (vector)"); | |
| 255 endif | |
| 4029 | 256 if (isvector (v)) |
| 3294 | 257 retval = sum (v) / length (v); |
| 258 else | |
| 259 error ("avg: expecting vector argument"); | |
| 260 endif | |
| 261 endfunction | |
| 262 @end group | |
| 263 @end example | |
| 264 | |
| 265 Although Octave does not automatically report an error if you call a | |
| 266 function with more arguments than expected, doing so probably indicates | |
| 267 that something is wrong. Octave also does not automatically report an | |
| 268 error if a function is called with too few arguments, but any attempt to | |
| 269 use a variable that has not been given a value will result in an error. | |
| 270 To avoid such problems and to provide useful messages, we check for both | |
| 271 possibilities and issue our own error message. | |
| 272 | |
| 4700 | 273 @DOCSTRING(nargin) |
| 3294 | 274 |
| 6558 | 275 @DOCSTRING(inputname) |
| 276 | |
| 3371 | 277 @DOCSTRING(silent_functions) |
| 3294 | 278 |
| 4167 | 279 @node Multiple Return Values |
| 3294 | 280 @section Multiple Return Values |
| 281 | |
| 282 Unlike many other computer languages, Octave allows you to define | |
| 283 functions that return more than one value. The syntax for defining | |
| 284 functions that return multiple values is | |
| 285 | |
| 286 @example | |
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287 @group |
| 3294 | 288 function [@var{ret-list}] = @var{name} (@var{arg-list}) |
| 289 @var{body} | |
| 290 endfunction | |
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291 @end group |
| 3294 | 292 @end example |
| 293 | |
| 294 @noindent | |
| 295 where @var{name}, @var{arg-list}, and @var{body} have the same meaning | |
| 296 as before, and @var{ret-list} is a comma-separated list of variable | |
| 297 names that will hold the values returned from the function. The list of | |
| 298 return values must have at least one element. If @var{ret-list} has | |
| 299 only one element, this form of the @code{function} statement is | |
| 300 equivalent to the form described in the previous section. | |
| 301 | |
| 302 Here is an example of a function that returns two values, the maximum | |
| 303 element of a vector and the index of its first occurrence in the vector. | |
| 304 | |
| 305 @example | |
| 306 @group | |
| 307 function [max, idx] = vmax (v) | |
| 308 idx = 1; | |
| 309 max = v (idx); | |
| 310 for i = 2:length (v) | |
| 311 if (v (i) > max) | |
| 312 max = v (i); | |
| 313 idx = i; | |
| 314 endif | |
| 315 endfor | |
| 316 endfunction | |
| 317 @end group | |
| 318 @end example | |
| 319 | |
| 320 In this particular case, the two values could have been returned as | |
| 321 elements of a single array, but that is not always possible or | |
| 322 convenient. The values to be returned may not have compatible | |
| 323 dimensions, and it is often desirable to give the individual return | |
| 324 values distinct names. | |
| 325 | |
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326 It is possible to use the @code{nthargout} function to obtain only some |
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327 of the return values or several at once in a cell array. |
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328 @xref{Cell Array Objects}. |
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329 |
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330 @DOCSTRING(nthargout) |
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331 |
| 3294 | 332 In addition to setting @code{nargin} each time a function is called, |
| 333 Octave also automatically initializes @code{nargout} to the number of | |
| 334 values that are expected to be returned. This allows you to write | |
| 335 functions that behave differently depending on the number of values that | |
| 336 the user of the function has requested. The implicit assignment to the | |
| 337 built-in variable @code{ans} does not figure in the count of output | |
| 338 arguments, so the value of @code{nargout} may be zero. | |
| 339 | |
| 340 The @code{svd} and @code{lu} functions are examples of built-in | |
| 341 functions that behave differently depending on the value of | |
| 342 @code{nargout}. | |
| 343 | |
| 344 It is possible to write functions that only set some return values. For | |
| 345 example, calling the function | |
| 346 | |
| 347 @example | |
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348 @group |
| 3294 | 349 function [x, y, z] = f () |
| 350 x = 1; | |
| 351 z = 2; | |
| 352 endfunction | |
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353 @end group |
| 3294 | 354 @end example |
| 355 | |
| 356 @noindent | |
| 357 as | |
| 358 | |
| 359 @example | |
| 360 [a, b, c] = f () | |
| 361 @end example | |
| 362 | |
| 363 @noindent | |
| 364 produces: | |
| 365 | |
| 366 @example | |
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367 @group |
| 3294 | 368 a = 1 |
| 369 | |
| 370 b = [](0x0) | |
| 371 | |
| 372 c = 2 | |
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373 @end group |
| 3294 | 374 @end example |
| 375 | |
| 376 @noindent | |
| 6501 | 377 along with a warning. |
| 3294 | 378 |
| 4700 | 379 @DOCSTRING(nargout) |
| 3294 | 380 |
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381 It is good practice at the head of a function to verify that it has been called |
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382 correctly. In Octave the following idiom is seen frequently |
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383 |
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384 @example |
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385 @group |
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386 if (nargin < min_#_inputs || nargin > max_#_inputs) |
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387 print_usage (); |
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388 endif |
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389 @end group |
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390 @end example |
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391 |
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392 @noindent |
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393 which stops the function execution and prints a message about the correct |
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394 way to call the function whenever the number of inputs is wrong. |
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395 |
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396 @DOCSTRING(validateattributes) |
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397 |
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398 For compatibility with @sc{matlab}, @code{nargchk}, @code{narginchk} and |
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399 @code{nargoutchk} are available which provide similar error checking. |
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400 |
| 3371 | 401 @DOCSTRING(nargchk) |
| 3294 | 402 |
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403 @DOCSTRING(narginchk) |
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404 |
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405 @DOCSTRING(nargoutchk) |
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406 |
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407 @anchor{XREFvarargin} @anchor{XREFvarargout} |
| 4167 | 408 @node Variable-length Argument Lists |
| 3294 | 409 @section Variable-length Argument Lists |
| 4933 | 410 @cindex variable-length argument lists |
| 8567 | 411 @cindex @code{varargin} |
| 8072 | 412 |
| 6510 | 413 Sometimes the number of input arguments is not known when the function |
| 414 is defined. As an example think of a function that returns the smallest | |
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415 of all its input arguments. For example: |
| 6510 | 416 |
| 417 @example | |
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418 @group |
| 6510 | 419 a = smallest (1, 2, 3); |
| 420 b = smallest (1, 2, 3, 4); | |
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421 @end group |
| 6510 | 422 @end example |
| 423 | |
| 424 @noindent | |
| 425 In this example both @code{a} and @code{b} would be 1. One way to write | |
| 426 the @code{smallest} function is | |
| 427 | |
| 428 @example | |
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429 @group |
| 6510 | 430 function val = smallest (arg1, arg2, arg3, arg4, arg5) |
| 431 @var{body} | |
| 432 endfunction | |
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433 @end group |
| 6510 | 434 @end example |
| 435 | |
| 436 @noindent | |
| 437 and then use the value of @code{nargin} to determine which of the input | |
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438 arguments should be considered. The problem with this approach is |
| 6510 | 439 that it can only handle a limited number of input arguments. |
| 440 | |
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441 If the special parameter name @code{varargin} appears at the end of a |
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442 function parameter list it indicates that the function takes a variable |
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443 number of input arguments. Using @code{varargin} the function |
| 6510 | 444 looks like this |
| 445 | |
| 446 @example | |
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447 @group |
| 6510 | 448 function val = smallest (varargin) |
| 449 @var{body} | |
| 450 endfunction | |
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451 @end group |
| 6510 | 452 @end example |
| 453 | |
| 454 @noindent | |
| 455 In the function body the input arguments can be accessed through the | |
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456 variable @code{varargin}. This variable is a cell array containing |
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457 all the input arguments. @xref{Cell Arrays}, for details on working |
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458 with cell arrays. The @code{smallest} function can now be defined |
| 6510 | 459 like this |
| 460 | |
| 461 @example | |
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462 @group |
| 6510 | 463 function val = smallest (varargin) |
| 464 val = min ([varargin@{:@}]); | |
| 465 endfunction | |
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466 @end group |
| 6510 | 467 @end example |
| 468 | |
| 469 @noindent | |
| 470 This implementation handles any number of input arguments, but it's also | |
| 471 a very simple solution to the problem. | |
| 472 | |
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473 A slightly more complex example of @code{varargin} is a function |
| 6510 | 474 @code{print_arguments} that prints all input arguments. Such a function |
| 475 can be defined like this | |
| 476 | |
| 477 @example | |
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478 @group |
| 6510 | 479 function print_arguments (varargin) |
| 480 for i = 1:length (varargin) | |
| 481 printf ("Input argument %d: ", i); | |
| 482 disp (varargin@{i@}); | |
| 483 endfor | |
| 484 endfunction | |
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485 @end group |
| 6510 | 486 @end example |
| 487 | |
| 488 @noindent | |
| 489 This function produces output like this | |
| 490 | |
| 491 @example | |
| 492 @group | |
| 493 print_arguments (1, "two", 3); | |
| 494 @print{} Input argument 1: 1 | |
| 495 @print{} Input argument 2: two | |
| 496 @print{} Input argument 3: 3 | |
| 497 @end group | |
| 498 @end example | |
| 3294 | 499 |
| 6558 | 500 @DOCSTRING(parseparams) |
| 501 | |
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502 @node Ignoring Arguments |
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503 @section Ignoring Arguments |
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504 |
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505 In the formal argument list, it is possible to use the dummy placeholder |
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506 @code{~} instead of a name. This indicates that the corresponding argument |
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507 value should be ignored and not stored to any variable. |
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508 |
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509 @example |
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510 @group |
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511 function val = pick2nd (~, arg2) |
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512 val = arg2; |
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513 endfunction |
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514 @end group |
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515 @end example |
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516 |
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517 The value of @code{nargin} is not affected by using this declaration. |
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518 |
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519 Return arguments can also be ignored using the same syntax. Functions may |
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520 take advantage of ignored outputs to reduce the number of calculations |
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521 performed. To do so, use the @code{isargout} function to query whether the |
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522 output argument is wanted. For example: |
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523 |
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524 @example |
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525 @group |
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526 function [out1, out2] = long_function (x, y, z) |
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527 if (isargout (1)) |
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528 ## Long calculation |
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529 @dots{} |
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530 out1 = result; |
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531 endif |
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532 @dots{} |
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533 endfunction |
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534 @end group |
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535 @end example |
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536 |
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537 @DOCSTRING(isargout) |
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538 |
| 4167 | 539 @node Variable-length Return Lists |
| 3294 | 540 @section Variable-length Return Lists |
| 4933 | 541 @cindex variable-length return lists |
| 8567 | 542 @cindex @code{varargout} |
| 8072 | 543 |
| 6510 | 544 It is possible to return a variable number of output arguments from a |
| 545 function using a syntax that's similar to the one used with the | |
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546 special @code{varargin} parameter name. To let a function return a |
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547 variable number of output arguments the special output parameter name |
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548 @code{varargout} is used. As with @code{varargin}, @code{varargout} is |
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549 a cell array that will contain the requested output arguments. |
| 6510 | 550 |
| 551 As an example the following function sets the first output argument to | |
| 552 1, the second to 2, and so on. | |
| 553 | |
| 554 @example | |
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555 @group |
| 6510 | 556 function varargout = one_to_n () |
| 557 for i = 1:nargout | |
| 558 varargout@{i@} = i; | |
| 559 endfor | |
| 560 endfunction | |
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561 @end group |
| 6510 | 562 @end example |
| 563 | |
| 564 @noindent | |
| 565 When called this function returns values like this | |
| 566 | |
| 567 @example | |
| 568 @group | |
| 569 [a, b, c] = one_to_n () | |
| 570 @result{} a = 1 | |
| 571 @result{} b = 2 | |
| 572 @result{} c = 3 | |
| 573 @end group | |
| 574 @end example | |
| 3294 | 575 |
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576 If @code{varargin} (@code{varargout}) does not appear as the last |
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577 element of the input (output) parameter list, then it is not special, |
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578 and is handled the same as any other parameter name. |
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579 |
| 6558 | 580 @DOCSTRING(deal) |
| 581 | |
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582 @node Returning from a Function |
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583 @section Returning from a Function |
| 3294 | 584 |
| 585 The body of a user-defined function can contain a @code{return} statement. | |
| 586 This statement returns control to the rest of the Octave program. It | |
| 587 looks like this: | |
| 588 | |
| 589 @example | |
| 590 return | |
| 591 @end example | |
| 592 | |
| 593 Unlike the @code{return} statement in C, Octave's @code{return} | |
| 594 statement cannot be used to return a value from a function. Instead, | |
| 595 you must assign values to the list of return variables that are part of | |
| 596 the @code{function} statement. The @code{return} statement simply makes | |
| 597 it easier to exit a function from a deeply nested loop or conditional | |
| 598 statement. | |
| 599 | |
| 600 Here is an example of a function that checks to see if any elements of a | |
| 601 vector are nonzero. | |
| 602 | |
| 603 @example | |
| 604 @group | |
| 605 function retval = any_nonzero (v) | |
| 606 retval = 0; | |
| 607 for i = 1:length (v) | |
| 608 if (v (i) != 0) | |
| 609 retval = 1; | |
| 610 return; | |
| 611 endif | |
| 612 endfor | |
| 613 printf ("no nonzero elements found\n"); | |
| 614 endfunction | |
| 615 @end group | |
| 616 @end example | |
| 617 | |
| 618 Note that this function could not have been written using the | |
| 619 @code{break} statement to exit the loop once a nonzero value is found | |
| 620 without adding extra logic to avoid printing the message if the vector | |
| 621 does contain a nonzero element. | |
| 622 | |
| 11547 | 623 @deftypefn {Keyword} {} return |
| 3294 | 624 When Octave encounters the keyword @code{return} inside a function or |
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625 script, it returns control to the caller immediately. At the top level, |
| 3294 | 626 the return statement is ignored. A @code{return} statement is assumed |
| 627 at the end of every function definition. | |
| 11547 | 628 @end deftypefn |
| 3294 | 629 |
| 6510 | 630 @node Default Arguments |
| 631 @section Default Arguments | |
| 632 @cindex default arguments | |
| 633 | |
| 634 Since Octave supports variable number of input arguments, it is very useful | |
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635 to assign default values to some input arguments. When an input argument |
| 6510 | 636 is declared in the argument list it is possible to assign a default |
| 637 value to the argument like this | |
| 638 | |
| 639 @example | |
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640 @group |
| 6510 | 641 function @var{name} (@var{arg1} = @var{val1}, @dots{}) |
| 642 @var{body} | |
| 643 endfunction | |
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644 @end group |
| 6510 | 645 @end example |
| 646 | |
| 647 @noindent | |
| 648 If no value is assigned to @var{arg1} by the user, it will have the | |
| 649 value @var{val1}. | |
| 650 | |
| 651 As an example, the following function implements a variant of the classic | |
| 652 ``Hello, World'' program. | |
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653 |
| 6510 | 654 @example |
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655 @group |
| 6510 | 656 function hello (who = "World") |
| 657 printf ("Hello, %s!\n", who); | |
| 658 endfunction | |
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659 @end group |
| 6510 | 660 @end example |
| 661 | |
| 662 @noindent | |
| 663 When called without an input argument the function prints the following | |
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664 |
| 6510 | 665 @example |
| 666 @group | |
| 667 hello (); | |
| 668 @print{} Hello, World! | |
| 669 @end group | |
| 670 @end example | |
| 671 | |
| 672 @noindent | |
| 673 and when it's called with an input argument it prints the following | |
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674 |
| 6510 | 675 @example |
| 676 @group | |
| 677 hello ("Beautiful World of Free Software"); | |
| 678 @print{} Hello, Beautiful World of Free Software! | |
| 679 @end group | |
| 680 @end example | |
| 681 | |
| 682 Sometimes it is useful to explicitly tell Octave to use the default value | |
| 683 of an input argument. This can be done writing a @samp{:} as the value | |
| 684 of the input argument when calling the function. | |
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685 |
| 6510 | 686 @example |
| 687 @group | |
| 688 hello (:); | |
| 689 @print{} Hello, World! | |
| 690 @end group | |
| 691 @end example | |
| 692 | |
| 4167 | 693 @node Function Files |
| 3294 | 694 @section Function Files |
| 695 @cindex function file | |
| 696 | |
| 697 Except for simple one-shot programs, it is not practical to have to | |
| 698 define all the functions you need each time you need them. Instead, you | |
| 699 will normally want to save them in a file so that you can easily edit | |
| 700 them, and save them for use at a later time. | |
| 701 | |
| 702 Octave does not require you to load function definitions from files | |
| 703 before using them. You simply need to put the function definitions in a | |
| 704 place where Octave can find them. | |
| 705 | |
| 706 When Octave encounters an identifier that is undefined, it first looks | |
| 707 for variables or functions that are already compiled and currently | |
| 708 listed in its symbol table. If it fails to find a definition there, it | |
| 6556 | 709 searches a list of directories (the @dfn{path}) for files ending in |
| 6554 | 710 @file{.m} that have the same base name as the undefined |
| 711 identifier.@footnote{The @samp{.m} suffix was chosen for compatibility | |
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712 with @sc{matlab}.} Once Octave finds a file with a name that matches, |
| 6554 | 713 the contents of the file are read. If it defines a @emph{single} |
| 714 function, it is compiled and executed. @xref{Script Files}, for more | |
| 715 information about how you can define more than one function in a single | |
| 716 file. | |
| 3294 | 717 |
| 718 When Octave defines a function from a function file, it saves the full | |
| 6554 | 719 name of the file it read and the time stamp on the file. If the time |
| 720 stamp on the file changes, Octave may reload the file. When Octave is | |
| 721 running interactively, time stamp checking normally happens at most once | |
| 722 each time Octave prints the prompt. Searching for new function | |
| 723 definitions also occurs if the current working directory changes. | |
| 3294 | 724 |
| 725 Checking the time stamp allows you to edit the definition of a function | |
| 726 while Octave is running, and automatically use the new function | |
| 6554 | 727 definition without having to restart your Octave session. |
| 3294 | 728 |
| 729 To avoid degrading performance unnecessarily by checking the time stamps | |
| 730 on functions that are not likely to change, Octave assumes that function | |
| 731 files in the directory tree | |
| 732 @file{@var{octave-home}/share/octave/@var{version}/m} | |
| 733 will not change, so it doesn't have to check their time stamps every time the | |
| 734 functions defined in those files are used. This is normally a very good | |
| 735 assumption and provides a significant improvement in performance for the | |
| 736 function files that are distributed with Octave. | |
| 737 | |
| 738 If you know that your own function files will not change while you are | |
| 6554 | 739 running Octave, you can improve performance by calling |
| 740 @code{ignore_function_time_stamp ("all")}, so that Octave will | |
| 741 ignore the time stamps for all function files. Passing | |
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742 @qcode{"system"} to this function resets the default behavior. |
| 3294 | 743 |
| 5775 | 744 @c FIXME -- note about time stamps on files in NFS environments? |
| 3294 | 745 |
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746 @DOCSTRING(edit) |
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747 |
| 6549 | 748 @DOCSTRING(mfilename) |
| 749 | |
| 6638 | 750 @DOCSTRING(ignore_function_time_stamp) |
| 751 | |
| 752 @menu | |
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753 * Manipulating the Load Path:: |
| 6638 | 754 * Subfunctions:: |
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755 * Private Functions:: |
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756 * Nested Functions:: |
| 6638 | 757 * Overloading and Autoloading:: |
| 758 * Function Locking:: | |
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759 * Function Precedence:: |
| 6638 | 760 @end menu |
| 761 | |
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762 @node Manipulating the Load Path |
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763 @subsection Manipulating the Load Path |
| 6638 | 764 |
| 8828 | 765 When a function is called, Octave searches a list of directories for |
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766 a file that contains the function declaration. This list of directories |
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767 is known as the load path. By default the load path contains |
| 6638 | 768 a list of directories distributed with Octave plus the current |
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769 working directory. To see your current load path call the @code{path} |
| 6638 | 770 function without any input or output arguments. |
| 771 | |
| 772 It is possible to add or remove directories to or from the load path | |
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773 using @code{addpath} and @code{rmpath}. As an example, the following |
| 6638 | 774 code adds @samp{~/Octave} to the load path. |
| 775 | |
| 776 @example | |
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777 addpath ("~/Octave") |
| 6638 | 778 @end example |
| 779 | |
| 780 @noindent | |
| 781 After this the directory @samp{~/Octave} will be searched for functions. | |
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782 |
| 6502 | 783 @DOCSTRING(addpath) |
| 784 | |
| 785 @DOCSTRING(genpath) | |
| 786 | |
| 787 @DOCSTRING(rmpath) | |
| 788 | |
| 789 @DOCSTRING(savepath) | |
| 790 | |
| 6477 | 791 @DOCSTRING(path) |
| 3294 | 792 |
| 6502 | 793 @DOCSTRING(pathdef) |
| 794 | |
| 795 @DOCSTRING(pathsep) | |
| 796 | |
| 3428 | 797 @DOCSTRING(rehash) |
| 798 | |
| 799 @DOCSTRING(file_in_loadpath) | |
| 800 | |
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801 @DOCSTRING(restoredefaultpath) |
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802 |
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803 @DOCSTRING(command_line_path) |
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804 |
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805 @DOCSTRING(find_dir_in_path) |
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806 |
| 6556 | 807 @node Subfunctions |
| 808 @subsection Subfunctions | |
| 809 | |
| 810 A function file may contain secondary functions called | |
| 811 @dfn{subfunctions}. These secondary functions are only visible to the | |
| 812 other functions in the same function file. For example, a file | |
| 813 @file{f.m} containing | |
| 814 | |
| 815 @example | |
| 816 @group | |
| 817 function f () | |
| 818 printf ("in f, calling g\n"); | |
| 819 g () | |
| 820 endfunction | |
| 821 function g () | |
| 822 printf ("in g, calling h\n"); | |
| 6638 | 823 h () |
| 6556 | 824 endfunction |
| 825 function h () | |
| 826 printf ("in h\n") | |
| 827 endfunction | |
| 828 @end group | |
| 829 @end example | |
| 830 | |
| 831 @noindent | |
| 832 defines a main function @code{f} and two subfunctions. The | |
| 833 subfunctions @code{g} and @code{h} may only be called from the main | |
| 834 function @code{f} or from the other subfunctions, but not from outside | |
| 835 the file @file{f.m}. | |
| 836 | |
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837 @node Private Functions |
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838 @subsection Private Functions |
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839 |
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840 In many cases one function needs to access one or more helper |
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841 functions. If the helper function is limited to the scope of a single |
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842 function, then subfunctions as discussed above might be used. However, |
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843 if a single helper function is used by more than one function, then |
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844 this is no longer possible. In this case the helper functions might |
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845 be placed in a subdirectory, called "private", of the directory in which |
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846 the functions needing access to this helper function are found. |
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847 |
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848 As a simple example, consider a function @code{func1}, that calls a helper |
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849 function @code{func2} to do much of the work. For example: |
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850 |
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851 @example |
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852 @group |
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853 function y = func1 (x) |
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854 y = func2 (x); |
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855 endfunction |
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856 @end group |
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857 @end example |
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858 |
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859 @noindent |
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860 Then if the path to @code{func1} is @code{<directory>/func1.m}, and if |
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862 then @code{func2} is only available for use of the functions, like |
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863 @code{func1}, that are found in @code{<directory>}. |
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864 |
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865 @node Nested Functions |
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866 @subsection Nested Functions |
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867 |
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868 Nested functions are similar to subfunctions in that only the main function is |
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869 visible outside the file. However, they also allow for child functions to |
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870 access the local variables in their parent function. This shared access mimics |
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871 using a global variable to share information --- but a global variable which is |
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872 not visible to the rest of Octave. As a programming strategy, sharing data |
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873 this way can create code which is difficult to maintain. It is recommended to |
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874 use subfunctions in place of nested functions when possible. |
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875 |
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876 As a simple example, consider a parent function @code{foo}, that calls a nested |
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877 child function @code{bar}, with a shared variable @var{x}. |
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878 |
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879 @example |
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880 @group |
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881 function y = foo () |
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882 x = 10; |
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883 bar (); |
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884 y = x; |
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885 |
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886 function bar () |
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887 x = 20; |
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888 endfunction |
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889 endfunction |
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890 |
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891 foo () |
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892 @result{} 20 |
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893 @end group |
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894 @end example |
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895 |
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896 @noindent |
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897 Notice that there is no special syntax for sharing @var{x}. This can lead to |
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898 problems with accidental variable sharing between a parent function and its |
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899 child. While normally variables are inherited, child function parameters and |
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900 return values are local to the child function. |
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901 |
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902 Now consider the function @code{foobar} that uses variables @var{x} and |
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903 @var{y}. @code{foobar} calls a nested function @code{foo} which takes |
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904 @var{x} as a parameter and returns @var{y}. @code{foo} then calls @code{bat} |
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905 which does some computation. |
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906 |
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907 @example |
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908 @group |
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909 function z = foobar () |
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910 x = 0; |
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911 y = 0; |
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912 z = foo (5); |
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913 z += x + y; |
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914 |
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915 function y = foo (x) |
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916 y = x + bat (); |
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917 |
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918 function z = bat () |
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919 z = x; |
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920 endfunction |
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921 endfunction |
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922 endfunction |
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923 |
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924 foobar () |
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925 @result{} 10 |
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926 @end group |
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927 @end example |
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928 |
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929 @noindent |
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930 It is important to note that the @var{x} and @var{y} in @code{foobar} remain |
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931 zero, as in @code{foo} they are a return value and parameter respectively. The |
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932 @var{x} in @code{bat} refers to the @var{x} in @code{foo}. |
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933 |
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934 Variable inheritance leads to a problem for @code{eval} and scripts. If a |
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935 new variable is created in a parent function, it is not clear what should happen |
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936 in nested child functions. For example, consider a parent function @code{foo} |
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937 with a nested child function @code{bar}: |
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938 |
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939 @example |
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940 @group |
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941 function y = foo (to_eval) |
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942 bar (); |
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943 eval (to_eval); |
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944 |
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945 function bar () |
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946 eval ("x = 100;"); |
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947 eval ("y = x;"); |
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948 endfunction |
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949 endfunction |
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950 |
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951 foo ("x = 5;") |
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952 @result{} error: can not add variable "x" to a static workspace |
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953 |
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954 foo ("y = 10;") |
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955 @result{} 10 |
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956 |
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957 foo ("") |
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958 @result{} 100 |
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959 @end group |
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960 @end example |
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961 |
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962 @noindent |
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963 The parent function @code{foo} is unable to create a new variable |
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964 @var{x}, but the child function @code{bar} was successful. Furthermore, even |
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965 in an @code{eval} statement @var{y} in @code{bar} is the same @var{y} as in its |
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966 parent function @code{foo}. The use of @code{eval} in conjunction with nested |
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967 functions is best avoided. |
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968 |
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969 As with subfunctions, only the first nested function in a file may be called |
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970 from the outside. Inside a function the rules are more complicated. In |
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971 general a nested function may call: |
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972 |
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973 @enumerate 0 |
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974 @item |
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975 Globally visible functions |
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976 |
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977 @item |
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978 Any function that the nested function's parent can call |
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979 |
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980 @item |
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981 Sibling functions (functions that have the same parents) |
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982 |
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983 @item |
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984 Direct children |
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985 |
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986 @end enumerate |
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987 |
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988 As a complex example consider a parent function @code{ex_top} with two |
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989 child functions, @code{ex_a} and @code{ex_b}. In addition, @code{ex_a} has two |
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990 more child functions, @code{ex_aa} and @code{ex_ab}. For example: |
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991 |
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992 @example |
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993 function ex_top () |
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994 ## Can call: ex_top, ex_a, and ex_b |
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995 ## Can NOT call: ex_aa and ex_ab |
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996 |
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997 function ex_a () |
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998 ## Call call everything |
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999 |
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1000 function ex_aa () |
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1001 ## Can call everything |
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1002 endfunction |
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1003 |
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1004 function ex_ab () |
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1005 ## Can call everything |
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1006 endfunction |
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1007 endfunction |
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1008 |
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1009 function ex_b () |
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1010 ## Can call: ex_top, ex_a, and ex_b |
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1011 ## Can NOT call: ex_aa and ex_ab |
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1012 endfunction |
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1013 endfunction |
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1014 @end example |
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1015 |
| 6635 | 1016 @node Overloading and Autoloading |
| 1017 @subsection Overloading and Autoloading | |
| 1018 | |
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1019 Functions can be overloaded to work with different input arguments. For |
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1020 example, the operator '+' has been overloaded in Octave to work with single, |
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1021 double, uint8, int32, and many other arguments. The preferred way to overload |
|
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1022 functions is through classes and object oriented programming |
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1023 (@pxref{Function Overloading}). Occasionally, however, one needs to undo |
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1024 user overloading and call the default function associated with a specific |
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1025 type. The @code{builtin} function exists for this purpose. |
| 6635 | 1026 |
| 1027 @DOCSTRING(builtin) | |
| 1028 | |
| 1029 A single dynamically linked file might define several | |
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1030 functions. However, as Octave searches for functions based on the |
| 6635 | 1031 functions filename, Octave needs a manner in which to find each of the |
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1032 functions in the dynamically linked file. On operating systems that |
| 6635 | 1033 support symbolic links, it is possible to create a symbolic link to the |
| 1034 original file for each of the functions which it contains. | |
| 1035 | |
| 1036 However, there is at least one well known operating system that doesn't | |
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1037 support symbolic links. Making copies of the original file for each of |
| 8828 | 1038 the functions is undesirable as it increases the |
|
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1039 amount of disk space used by Octave. Instead Octave supplies the |
| 6635 | 1040 @code{autoload} function, that permits the user to define in which |
| 1041 file a certain function will be found. | |
| 1042 | |
| 1043 @DOCSTRING(autoload) | |
| 1044 | |
| 1045 @node Function Locking | |
| 1046 @subsection Function Locking | |
| 1047 | |
| 1048 It is sometime desirable to lock a function into memory with the | |
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1049 @code{mlock} function. This is typically used for dynamically linked |
| 6899 | 1050 functions in Oct-files or mex-files that contain some initialization, |
| 1051 and it is desirable that calling @code{clear} does not remove this | |
| 6635 | 1052 initialization. |
| 1053 | |
| 6899 | 1054 As an example, |
| 1055 | |
| 1056 @example | |
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1057 @group |
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1058 function my_function () |
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1059 mlock (); |
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1060 @dots{} |
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1061 @end group |
| 6899 | 1062 @end example |
| 1063 | |
| 1064 @noindent | |
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1065 prevents @code{my_function} from being removed from memory after it is |
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1066 called, even if @code{clear} is called. It is possible to determine if |
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1067 a function is locked into memory with the @code{mislocked}, and to unlock |
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1068 a function with @code{munlock}, which the following illustrates. |
| 6899 | 1069 |
| 1070 @example | |
| 1071 @group | |
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1072 my_function (); |
| 6899 | 1073 mislocked ("my_function") |
| 1074 @result{} ans = 1 | |
| 1075 munlock ("my_function"); | |
| 1076 mislocked ("my_function") | |
| 1077 @result{} ans = 0 | |
| 1078 @end group | |
| 1079 @end example | |
| 1080 | |
| 1081 A common use of @code{mlock} is to prevent persistent variables from | |
| 8828 | 1082 being removed from memory, as the following example shows: |
| 6899 | 1083 |
| 1084 @example | |
| 1085 @group | |
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1086 function count_calls () |
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1087 mlock (); |
| 6899 | 1088 persistent calls = 0; |
| 7031 | 1089 printf ("'count_calls' has been called %d times\n", |
| 1090 ++calls); | |
| 6899 | 1091 endfunction |
| 1092 | |
| 1093 count_calls (); | |
| 1094 @print{} 'count_calls' has been called 1 times | |
| 1095 | |
| 1096 clear count_calls | |
| 1097 count_calls (); | |
| 1098 @print{} 'count_calls' has been called 2 times | |
| 1099 @end group | |
| 1100 @end example | |
| 1101 | |
| 1102 @code{mlock} might equally be used to prevent changes to a function from having | |
| 6635 | 1103 effect in Octave, though a similar effect can be had with the |
| 1104 @code{ignore_function_time_stamp} function. | |
| 1105 | |
| 1106 @DOCSTRING(mlock) | |
| 1107 | |
| 1108 @DOCSTRING(munlock) | |
| 1109 | |
| 1110 @DOCSTRING(mislocked) | |
| 1111 | |
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1112 @node Function Precedence |
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1113 @subsection Function Precedence |
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1114 |
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1115 Given the numerous different ways that Octave can define a function, it |
|
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1116 is possible and even likely that multiple versions of a function, might be |
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1117 defined within a particular scope. The precedence of which function will be |
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1118 used within a particular scope is given by |
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1119 |
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1120 @enumerate 1 |
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1121 @item Subfunction |
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1122 A subfunction with the required function name in the given scope. |
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1123 |
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1124 @item Private function |
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1125 A function defined within a private directory of the directory |
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1126 which contains the current function. |
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1127 |
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1128 @item Class constructor |
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1129 A function that constuctors a user class as defined in chapter |
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1130 @ref{Object Oriented Programming}. |
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1131 |
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1132 @item Class method |
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1133 An overloaded function of a class as in chapter |
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1134 @ref{Object Oriented Programming}. |
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1135 |
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1136 @item Command-line Function |
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1137 A function that has been defined on the command-line. |
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1138 |
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1139 @item Autoload function |
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1140 A function that is marked as autoloaded with @xref{XREFautoload,,autoload}. |
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1141 |
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1142 @item A Function on the Path |
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1143 A function that can be found on the users load-path. There can also be |
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1144 Oct-file, mex-file or m-file versions of this function and the precedence |
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1145 between these versions are in that order. |
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1146 |
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1147 @item Built-in function |
|
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1148 A function that is a part of core Octave such as @code{numel}, @code{size}, |
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1149 etc. |
|
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1150 @end enumerate |
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1151 |
| 4167 | 1152 @node Script Files |
| 3294 | 1153 @section Script Files |
| 1154 | |
| 1155 A script file is a file containing (almost) any sequence of Octave | |
| 1156 commands. It is read and evaluated just as if you had typed each | |
| 1157 command at the Octave prompt, and provides a convenient way to perform a | |
| 1158 sequence of commands that do not logically belong inside a function. | |
| 1159 | |
| 1160 Unlike a function file, a script file must @emph{not} begin with the | |
| 1161 keyword @code{function}. If it does, Octave will assume that it is a | |
| 1162 function file, and that it defines a single function that should be | |
| 1163 evaluated as soon as it is defined. | |
| 1164 | |
| 1165 A script file also differs from a function file in that the variables | |
| 1166 named in a script file are not local variables, but are in the same | |
| 1167 scope as the other variables that are visible on the command line. | |
| 1168 | |
| 1169 Even though a script file may not begin with the @code{function} | |
| 1170 keyword, it is possible to define more than one function in a single | |
|
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1171 script file and load (but not execute) all of them at once. To do |
| 3294 | 1172 this, the first token in the file (ignoring comments and other white |
| 1173 space) must be something other than @code{function}. If you have no | |
| 1174 other statements to evaluate, you can use a statement that has no | |
| 1175 effect, like this: | |
| 1176 | |
| 1177 @example | |
| 1178 @group | |
| 1179 # Prevent Octave from thinking that this | |
| 1180 # is a function file: | |
| 1181 | |
| 1182 1; | |
| 1183 | |
| 1184 # Define function one: | |
| 1185 | |
| 1186 function one () | |
|
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|
1187 @dots{} |
| 3294 | 1188 @end group |
| 1189 @end example | |
| 1190 | |
| 1191 To have Octave read and compile these functions into an internal form, | |
| 6638 | 1192 you need to make sure that the file is in Octave's load path |
| 6477 | 1193 (accessible through the @code{path} function), then simply type the |
| 1194 base name of the file that contains the commands. (Octave uses the | |
| 1195 same rules to search for script files as it does to search for | |
| 1196 function files.) | |
| 3294 | 1197 |
| 1198 If the first token in a file (ignoring comments) is @code{function}, | |
| 1199 Octave will compile the function and try to execute it, printing a | |
| 1200 message warning about any non-whitespace characters that appear after | |
| 1201 the function definition. | |
| 1202 | |
| 1203 Note that Octave does not try to look up the definition of any identifier | |
| 1204 until it needs to evaluate it. This means that Octave will compile the | |
| 1205 following statements if they appear in a script file, or are typed at | |
| 1206 the command line, | |
| 1207 | |
| 1208 @example | |
| 1209 @group | |
| 1210 # not a function file: | |
| 1211 1; | |
| 1212 function foo () | |
| 1213 do_something (); | |
| 1214 endfunction | |
| 1215 function do_something () | |
| 1216 do_something_else (); | |
| 1217 endfunction | |
| 1218 @end group | |
| 1219 @end example | |
| 1220 | |
| 1221 @noindent | |
| 1222 even though the function @code{do_something} is not defined before it is | |
| 1223 referenced in the function @code{foo}. This is not an error because | |
| 1224 Octave does not need to resolve all symbols that are referenced by a | |
| 1225 function until the function is actually evaluated. | |
| 1226 | |
| 1227 Since Octave doesn't look for definitions until they are needed, the | |
| 1228 following code will always print @samp{bar = 3} whether it is typed | |
| 1229 directly on the command line, read from a script file, or is part of a | |
| 1230 function body, even if there is a function or script file called | |
| 6477 | 1231 @file{bar.m} in Octave's path. |
| 3294 | 1232 |
| 1233 @example | |
| 1234 @group | |
| 1235 eval ("bar = 3"); | |
| 1236 bar | |
| 1237 @end group | |
| 1238 @end example | |
| 1239 | |
| 1240 Code like this appearing within a function body could fool Octave if | |
| 1241 definitions were resolved as the function was being compiled. It would | |
| 1242 be virtually impossible to make Octave clever enough to evaluate this | |
| 1243 code in a consistent fashion. The parser would have to be able to | |
| 1244 perform the call to @code{eval} at compile time, and that would be | |
| 1245 impossible unless all the references in the string to be evaluated could | |
| 1246 also be resolved, and requiring that would be too restrictive (the | |
| 1247 string might come from user input, or depend on things that are not | |
| 1248 known until the function is evaluated). | |
| 1249 | |
| 1250 Although Octave normally executes commands from script files that have | |
| 1251 the name @file{@var{file}.m}, you can use the function @code{source} to | |
| 1252 execute commands from any file. | |
| 1253 | |
| 3371 | 1254 @DOCSTRING(source) |
| 3294 | 1255 |
|
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1256 @node Function Handles Anonymous Functions Inline Functions |
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1257 @section Function Handles, Anonymous Functions, Inline Functions |
| 4933 | 1258 @cindex handle, function handles |
|
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1259 @cindex anonymous functions |
| 4933 | 1260 @cindex inline, inline functions |
| 1261 | |
| 6638 | 1262 It can be very convenient store a function in a variable so that it |
|
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|
1263 can be passed to a different function. For example, a function that |
|
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1264 performs numerical minimization needs access to the function that |
|
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|
1265 should be minimized. |
| 4933 | 1266 |
| 1267 @menu | |
| 1268 * Function Handles:: | |
| 6554 | 1269 * Anonymous Functions:: |
| 4933 | 1270 * Inline Functions:: |
| 1271 @end menu | |
| 1272 | |
| 1273 @node Function Handles | |
| 1274 @subsection Function Handles | |
| 1275 | |
| 6554 | 1276 A function handle is a pointer to another function and is defined with |
| 1277 the syntax | |
| 1278 | |
| 1279 @example | |
| 1280 @@@var{function-name} | |
| 1281 @end example | |
| 1282 | |
| 1283 @noindent | |
|
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|
1284 For example, |
| 6554 | 1285 |
| 1286 @example | |
| 6556 | 1287 f = @@sin; |
| 6554 | 1288 @end example |
| 1289 | |
| 1290 @noindent | |
|
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|
1291 creates a function handle called @code{f} that refers to the |
| 6554 | 1292 function @code{sin}. |
| 1293 | |
| 1294 Function handles are used to call other functions indirectly, or to pass | |
| 1295 a function as an argument to another function like @code{quad} or | |
|
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|
1296 @code{fsolve}. For example: |
| 6554 | 1297 |
| 1298 @example | |
|
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|
1299 @group |
| 6556 | 1300 f = @@sin; |
| 6554 | 1301 quad (f, 0, pi) |
| 6929 | 1302 @result{} 2 |
|
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|
1303 @end group |
| 6554 | 1304 @end example |
| 1305 | |
| 1306 You may use @code{feval} to call a function using function handle, or | |
| 6570 | 1307 simply write the name of the function handle followed by an argument |
| 6554 | 1308 list. If there are no arguments, you must use an empty argument list |
|
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|
1309 @samp{()}. For example: |
| 6554 | 1310 |
| 1311 @example | |
|
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|
1312 @group |
| 6556 | 1313 f = @@sin; |
| 6554 | 1314 feval (f, pi/4) |
| 6570 | 1315 @result{} 0.70711 |
| 6554 | 1316 f (pi/4) |
| 6570 | 1317 @result{} 0.70711 |
|
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|
1318 @end group |
| 6554 | 1319 @end example |
| 1320 | |
|
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1321 @DOCSTRING(is_function_handle) |
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|
1322 |
| 4933 | 1323 @DOCSTRING(functions) |
| 1324 | |
| 1325 @DOCSTRING(func2str) | |
| 1326 | |
| 1327 @DOCSTRING(str2func) | |
| 1328 | |
| 6570 | 1329 @node Anonymous Functions |
| 6554 | 1330 @subsection Anonymous Functions |
| 1331 | |
| 1332 Anonymous functions are defined using the syntax | |
| 1333 | |
| 1334 @example | |
| 1335 @@(@var{argument-list}) @var{expression} | |
| 1336 @end example | |
| 1337 | |
| 1338 @noindent | |
| 1339 Any variables that are not found in the argument list are inherited from | |
| 1340 the enclosing scope. Anonymous functions are useful for creating simple | |
| 1341 unnamed functions from expressions or for wrapping calls to other | |
| 1342 functions to adapt them for use by functions like @code{quad}. For | |
| 1343 example, | |
| 1344 | |
| 1345 @example | |
|
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|
1346 @group |
| 6554 | 1347 f = @@(x) x.^2; |
| 1348 quad (f, 0, 10) | |
| 6570 | 1349 @result{} 333.33 |
|
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|
1350 @end group |
| 6554 | 1351 @end example |
| 1352 | |
| 1353 @noindent | |
| 1354 creates a simple unnamed function from the expression @code{x.^2} and | |
| 1355 passes it to @code{quad}, | |
| 1356 | |
| 1357 @example | |
|
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|
1358 @group |
| 6554 | 1359 quad (@@(x) sin (x), 0, pi) |
| 6933 | 1360 @result{} 2 |
|
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|
1361 @end group |
| 6554 | 1362 @end example |
| 1363 | |
| 1364 @noindent | |
| 1365 wraps another function, and | |
| 1366 | |
| 1367 @example | |
|
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|
1368 @group |
| 6554 | 1369 a = 1; |
| 1370 b = 2; | |
| 1371 quad (@@(x) betainc (x, a, b), 0, 0.4) | |
| 6929 | 1372 @result{} 0.13867 |
|
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|
1373 @end group |
| 6554 | 1374 @end example |
| 1375 | |
| 1376 @noindent | |
| 1377 adapts a function with several parameters to the form required by | |
| 1378 @code{quad}. In this example, the values of @var{a} and @var{b} that | |
| 1379 are passed to @code{betainc} are inherited from the current | |
| 1380 environment. | |
| 1381 | |
| 4933 | 1382 @node Inline Functions |
| 1383 @subsection Inline Functions | |
| 1384 | |
| 6638 | 1385 An inline function is created from a string containing the function |
|
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|
1386 body using the @code{inline} function. The following code defines the |
| 6638 | 1387 function @math{f(x) = x^2 + 2}. |
| 1388 | |
| 1389 @example | |
|
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|
1390 f = inline ("x^2 + 2"); |
| 6638 | 1391 @end example |
| 1392 | |
| 1393 @noindent | |
| 1394 After this it is possible to evaluate @math{f} at any @math{x} by | |
| 1395 writing @code{f(x)}. | |
| 1396 | |
| 4933 | 1397 @DOCSTRING(inline) |
| 1398 | |
| 1399 @DOCSTRING(argnames) | |
| 1400 | |
| 1401 @DOCSTRING(formula) | |
| 1402 | |
|
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|
1403 @DOCSTRING(symvar) |
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|
1404 |
| 6549 | 1405 @node Commands |
| 1406 @section Commands | |
| 1407 | |
| 6638 | 1408 Commands are a special class of functions that only accept string |
|
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|
1409 input arguments. A command can be called as an ordinary function, but |
|
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|
1410 it can also be called without the parentheses. For example, |
| 6638 | 1411 |
| 1412 @example | |
| 1413 my_command hello world | |
| 1414 @end example | |
| 1415 | |
| 1416 @noindent | |
|
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1417 is equivalent to |
| 6638 | 1418 |
| 1419 @example | |
|
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|
1420 my_command ("hello", "world") |
| 6638 | 1421 @end example |
| 1422 | |
|
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1423 @noindent |
| 6638 | 1424 The general form of a command call is |
| 1425 | |
| 1426 @example | |
|
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|
1427 @var{cmdname} @var{arg1} @var{arg2} @dots{} |
| 6638 | 1428 @end example |
| 1429 | |
| 1430 @noindent | |
| 1431 which translates directly to | |
| 1432 | |
| 1433 @example | |
|
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1434 @var{cmdname} ("@var{arg1}", "@var{arg2}", @dots{}) |
| 6638 | 1435 @end example |
| 1436 | |
|
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1437 Any regular function can be used as a command if it accepts string input |
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1438 arguments. For example: |
|
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1439 |
| 6638 | 1440 @example |
|
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1441 @group |
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|
1442 toupper lower_case_arg |
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|
1443 @result{} ans = LOWER_CASE_ARG |
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1444 @end group |
| 6638 | 1445 @end example |
| 1446 | |
| 1447 One difficulty of commands occurs when one of the string input arguments | |
|
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1448 is stored in a variable. Because Octave can't tell the difference between |
|
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1449 a variable name and an ordinary string, it is not possible to pass a |
|
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1450 variable as input to a command. In such a situation a command must be |
|
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1451 called as a function. For example: |
| 6549 | 1452 |
|
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1453 @example |
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1454 @group |
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|
1455 strvar = "hello world"; |
|
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1456 toupper strvar |
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1457 @result{} ans = STRVAR |
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1458 toupper (strvar) |
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1459 @result{} ans = HELLO WORLD |
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1460 @end group |
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|
1461 @end example |
| 6549 | 1462 |
| 1463 | |
| 4167 | 1464 @node Organization of Functions |
| 3294 | 1465 @section Organization of Functions Distributed with Octave |
| 1466 | |
| 1467 Many of Octave's standard functions are distributed as function files. | |
| 1468 They are loosely organized by topic, in subdirectories of | |
| 1469 @file{@var{octave-home}/lib/octave/@var{version}/m}, to make it easier | |
| 1470 to find them. | |
| 1471 | |
| 1472 The following is a list of all the function file subdirectories, and the | |
| 1473 types of functions you will find there. | |
| 1474 | |
| 1475 @table @file | |
| 1476 @item audio | |
| 1477 Functions for playing and recording sounds. | |
| 1478 | |
|
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1479 @item deprecated |
|
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|
1480 Out-of-date functions which will eventually be removed from Octave. |
| 3294 | 1481 |
| 1482 @item elfun | |
|
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|
1483 Elementary functions, principally trigonometric. |
| 3294 | 1484 |
|
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1485 @item @@ftp |
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1486 Class functions for the FTP object. |
| 6554 | 1487 |
| 3294 | 1488 @item general |
| 1489 Miscellaneous matrix manipulations, like @code{flipud}, @code{rot90}, | |
| 1490 and @code{triu}, as well as other basic functions, like | |
| 4029 | 1491 @code{ismatrix}, @code{nargchk}, etc. |
| 3294 | 1492 |
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1493 @item geometry |
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1494 Functions related to Delaunay triangulation. |
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1495 |
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1496 @item help |
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1497 Functions for Octave's built-in help system. |
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1498 |
| 3294 | 1499 @item image |
| 1500 Image processing tools. These functions require the X Window System. | |
| 1501 | |
| 1502 @item io | |
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1503 Input-output functions. |
| 3294 | 1504 |
| 1505 @item linear-algebra | |
| 1506 Functions for linear algebra. | |
| 1507 | |
| 1508 @item miscellaneous | |
| 1509 Functions that don't really belong anywhere else. | |
| 1510 | |
| 6554 | 1511 @item optimization |
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1512 Functions related to minimization, optimization, and root finding. |
| 6554 | 1513 |
| 1514 @item path | |
| 1515 Functions to manage the directory path Octave uses to find functions. | |
| 1516 | |
| 1517 @item pkg | |
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1518 Package manager for installing external packages of functions in Octave. |
| 6554 | 1519 |
| 3294 | 1520 @item plot |
| 6556 | 1521 Functions for displaying and printing two- and three-dimensional graphs. |
| 3294 | 1522 |
| 1523 @item polynomial | |
| 1524 Functions for manipulating polynomials. | |
| 1525 | |
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1526 @item prefs |
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1527 Functions implementing user-defined preferences. |
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1528 |
| 3294 | 1529 @item set |
| 1530 Functions for creating and manipulating sets of unique values. | |
| 1531 | |
| 1532 @item signal | |
| 1533 Functions for signal processing applications. | |
| 1534 | |
| 6554 | 1535 @item sparse |
| 1536 Functions for handling sparse matrices. | |
| 1537 | |
| 3294 | 1538 @item specfun |
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1539 Special functions such as @code{bessel} or @code{factor}. |
| 3294 | 1540 |
| 1541 @item special-matrix | |
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1542 Functions that create special matrix forms such as Hilbert or Vandermonde |
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1543 matrices. |
| 3294 | 1544 |
| 1545 @item startup | |
| 1546 Octave's system-wide startup file. | |
| 1547 | |
| 1548 @item statistics | |
| 1549 Statistical functions. | |
| 1550 | |
| 1551 @item strings | |
| 1552 Miscellaneous string-handling functions. | |
| 1553 | |
| 6554 | 1554 @item testfun |
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1555 Functions for performing unit tests on other functions. |
| 6554 | 1556 |
| 3294 | 1557 @item time |
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1558 Functions related to time and date processing. |
| 3294 | 1559 @end table |