Mercurial > octave-nkf
annotate doc/interpreter/tips.txi @ 9486:d85a43495faa
update coding tips
| author | Jaroslav Hajek <highegg@gmail.com> |
|---|---|
| date | Wed, 05 Aug 2009 08:47:48 +0200 |
| parents | b2133f97079d |
| children | 09da0bd91412 |
| rev | line source |
|---|---|
| 8920 | 1 @c Copyright (C) 1996, 1997, 1999, 2002, 2004, 2005, 2007, 2008, |
| 2 @c 2009 John W. Eaton | |
| 7018 | 3 @c |
| 4 @c This file is part of Octave. | |
| 5 @c | |
| 6 @c Octave is free software; you can redistribute it and/or modify it | |
| 7 @c under the terms of the GNU General Public License as published by the | |
| 8 @c Free Software Foundation; either version 3 of the License, or (at | |
| 9 @c your option) any later version. | |
| 10 @c | |
| 11 @c Octave is distributed in the hope that it will be useful, but WITHOUT | |
| 12 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 @c for more details. | |
| 15 @c | |
| 16 @c You should have received a copy of the GNU General Public License | |
| 17 @c along with Octave; see the file COPYING. If not, see | |
| 18 @c <http://www.gnu.org/licenses/>. | |
| 3294 | 19 |
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20 @node Tips and Standards |
| 3294 | 21 @appendix Tips and Standards |
| 22 @cindex tips | |
| 23 @cindex standards of coding style | |
| 24 @cindex coding standards | |
| 25 | |
| 26 This chapter describes no additional features of Octave. Instead it | |
| 27 gives advice on making effective use of the features described in the | |
| 28 previous chapters. | |
| 29 | |
| 30 @menu | |
| 31 * Style Tips:: Writing clean and robust programs. | |
| 32 * Coding Tips:: Making code run faster. | |
| 33 * Comment Tips:: Conventions for writing comments. | |
| 34 * Function Headers:: Standard headers for functions. | |
| 6574 | 35 * Documentation Tips:: Writing readable documentation strings. |
| 3294 | 36 @end menu |
| 37 | |
| 4167 | 38 @node Style Tips |
| 3294 | 39 @section Writing Clean Octave Programs |
| 40 | |
| 41 Here are some tips for avoiding common errors in writing Octave code | |
| 42 intended for widespread use: | |
| 43 | |
| 44 @itemize @bullet | |
| 45 @item | |
| 46 Since all global variables share the same name space, and all functions | |
| 47 share another name space, you should choose a short word to distinguish | |
| 48 your program from other Octave programs. Then take care to begin the | |
| 49 names of all global variables, constants, and functions with the chosen | |
| 50 prefix. This helps avoid name conflicts. | |
| 51 | |
| 52 If you write a function that you think ought to be added to Octave under | |
| 53 a certain name, such as @code{fiddle_matrix}, don't call it by that name | |
| 54 in your program. Call it @code{mylib_fiddle_matrix} in your program, | |
| 5041 | 55 and send mail to @email{maintainers@@octave.org} suggesting that it |
| 3294 | 56 be added to Octave. If and when it is, the name can be changed easily |
| 57 enough. | |
| 58 | |
| 59 If one prefix is insufficient, your package may use two or three | |
| 60 alternative common prefixes, so long as they make sense. | |
| 61 | |
| 62 Separate the prefix from the rest of the symbol name with an underscore | |
| 63 @samp{_}. This will be consistent with Octave itself and with most | |
| 64 Octave programs. | |
| 65 | |
| 66 @item | |
| 67 When you encounter an error condition, call the function @code{error} | |
| 68 (or @code{usage}). The @code{error} and @code{usage} functions do not | |
| 69 return. | |
| 70 @xref{Errors}. | |
| 71 | |
| 72 @item | |
| 73 Please put a copyright notice on the file if you give copies to anyone. | |
| 74 Use the same lines that appear at the top of the function files | |
| 75 distributed with Octave. If you have not signed papers to assign the | |
| 76 copyright to anyone else, then place your name in the copyright notice. | |
| 77 @end itemize | |
| 78 | |
| 4167 | 79 @node Coding Tips |
| 3294 | 80 @section Tips for Making Code Run Faster. |
| 81 @cindex execution speed | |
| 82 @cindex speedups | |
| 83 | |
| 84 Here are some ways of improving the execution speed of Octave programs. | |
| 85 | |
| 86 @itemize @bullet | |
| 87 @item | |
| 9356 | 88 Vectorize loops. For instance, rather than |
| 89 @example | |
| 90 for i = 1:n-1 | |
| 91 a(i) = b(i+1) - b(i); | |
| 92 endfor | |
| 93 @end example | |
| 94 | |
| 95 write | |
| 96 | |
| 97 @example | |
| 98 a = b(2:n) - b(1:n-1); | |
| 99 @end example | |
| 100 | |
| 101 This is especially important for loops with "cheap" bodies. Often it suffices to vectorize | |
| 102 just the innermost loop to get acceptable performance. A general rule of thumb is that the | |
| 103 "order" of the vectorized body should be greater or equal to the "order" of the enclosing loop. | |
| 104 | |
| 105 @item | |
| 106 Use built-in and library functions if possible. Built-in and compiled functions are very fast. | |
| 107 Even with a m-file library function, chances are good that it is already optimized, or will be | |
| 108 optimized more in a future release. | |
| 109 | |
| 110 @item | |
| 111 Avoid computing costly intermediate results multiple times. Octave currently | |
| 112 does not eliminate common subexpressions. | |
| 9486 | 113 Also, certain internal computation results are cached for variables. |
| 114 For instance, if a matrix variable is used multiple times as an index, | |
| 115 checking the indices (and internal conversion to integers) is only done once. | |
| 3294 | 116 |
| 117 @item | |
| 9356 | 118 Be aware of lazy copies (copy-on-write). When a copy of an object |
| 119 is created, the data is not immediately copied, but rather shared. The actual | |
| 120 copying is postponed until the copied data needs to be modified. For example: | |
| 121 | |
| 122 @example | |
| 123 a = zeros (1000); # create a 1000x1000 matrix | |
| 124 b = a; # no copying done here | |
| 125 b(1) = 1; # copying done here | |
| 126 @end example | |
| 127 | |
| 128 Lazy copying applies to whole Octave objects such as matrices, cells, struct, | |
| 129 and also individual cell or struct elements (not array elements). | |
| 130 | |
| 131 Additionally, index expressions also use lazy copying when Octave can determine | |
| 132 that the indexed portion is contiguous in memory. For example: | |
| 133 | |
| 134 @example | |
| 135 a = zeros (1000); # create a 1000x1000 matrix | |
| 136 b = a(:,10:100); # no copying done here | |
| 137 b = a(10:100,:); # copying done here | |
| 138 @end example | |
| 139 | |
| 140 This applies to arrays (matrices), cell arrays, and structs indexed using (). | |
| 141 Index expressions generating cs-lists can also benefit of shallow copying | |
| 142 in some cases. In particular, when @var{a} is a struct array, expressions like | |
| 143 @code{@{a.x@}, @{a(:,2).x@}} will use lazy copying, so that data can be shared | |
| 144 between a struct array and a cell array. | |
| 145 | |
| 146 Most indexing expressions do not live longer than their `parent' objects. | |
| 147 In rare cases, however, a lazily copied slice outlasts its parent, in which | |
| 148 case it becomes orphaned, still occupying unnecessarily more memory than needed. | |
| 149 To provide a remedy working in most real cases, | |
| 150 Octave checks for orphaned lazy slices at certain situations, when a value | |
| 151 is stored into a "permanent" location, such as a named variable or cell or | |
| 152 struct element, and possibly economizes them. For example | |
| 153 | |
| 154 @example | |
| 155 a = zeros (1000); # create a 1000x1000 matrix | |
| 156 b = a(:,10:100); # lazy slice | |
| 157 a = []; # the original a array is still allocated | |
| 158 c@{1@} = b; # b is reallocated at this point | |
| 159 @end example | |
| 3294 | 160 |
| 161 @item | |
| 9356 | 162 Avoid deep recursion. Function calls to m-file functions carry a relatively significant overhead, |
| 163 so rewriting a recursion as a loop often helps. Also, note that the maximum level of recursion is | |
| 164 limited. | |
| 165 | |
| 166 @item | |
| 167 Avoid resizing matrices unnecessarily. When building a single result | |
| 3294 | 168 matrix from a series of calculations, set the size of the result matrix |
| 169 first, then insert values into it. Write | |
| 170 | |
| 171 @example | |
| 172 @group | |
| 173 result = zeros (big_n, big_m) | |
| 174 for i = over:and_over | |
| 175 r1 = @dots{} | |
| 176 r2 = @dots{} | |
| 177 result (r1, r2) = new_value (); | |
| 178 endfor | |
| 179 @end group | |
| 180 @end example | |
| 181 | |
| 182 @noindent | |
| 183 instead of | |
| 184 | |
| 185 @example | |
| 186 @group | |
| 187 result = []; | |
| 188 for i = ever:and_ever | |
| 189 result = [ result, new_value() ]; | |
| 190 endfor | |
| 191 @end group | |
| 192 @end example | |
| 193 | |
| 9356 | 194 Sometimes the number of items can't be computed in advance, and stack-like operations |
| 195 are needed. When elements are being repeatedly inserted at/removed from the end of an | |
| 196 array, Octave detects it as stack usage and attempts to use a smarter memory management | |
| 197 strategy preallocating the array in bigger chunks. Likewise works for cell and | |
| 198 struct arrays. | |
| 199 | |
| 200 @example | |
| 201 a = []; | |
| 202 while (condition) | |
| 203 @dots{} | |
| 204 a(end+1) = value; # "push" operation | |
| 205 @dots{} | |
| 206 a(end) = []; # "pop" operation | |
| 207 @dots{} | |
| 208 endwhile | |
| 209 @end example | |
| 210 | |
| 3294 | 211 @item |
| 9356 | 212 Use @code{cellfun} intelligently. The @code{cellfun} function is a useful tool |
| 213 for avoiding loops. @xref{Processing Data in Cell Arrays}. | |
| 214 @code{cellfun} is often use with anonymous function handles; however, calling | |
| 215 an anonymous function involves an overhead quite comparable to the overhead | |
| 216 of an m-file function. Passing a handle to a built-in function is faster, | |
| 217 because the interpreter is not involved in the internal loop. For example: | |
| 218 | |
| 219 @example | |
| 220 a = @{@dots{}@} | |
| 221 v = cellfun (@@(x) det(x), a); # compute determinants | |
| 222 v = cellfun (@@det, a); # faster | |
| 223 @end example | |
| 224 | |
| 225 @item | |
| 226 Avoid calling @code{eval} or @code{feval} excessively, because | |
| 3294 | 227 they require Octave to parse input or look up the name of a function in |
| 228 the symbol table. | |
| 229 | |
| 230 If you are using @code{eval} as an exception handling mechanism and not | |
| 231 because you need to execute some arbitrary text, use the @code{try} | |
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232 statement instead. @xref{The @code{try} Statement}. |
| 3294 | 233 |
| 234 @item | |
| 235 If you are calling lots of functions but none of them will need to | |
| 236 change during your run, set the variable | |
| 237 @code{ignore_function_time_stamp} to @code{"all"} so that Octave doesn't | |
| 238 waste a lot of time checking to see if you have updated your function | |
| 239 files. | |
| 240 @end itemize | |
| 241 | |
| 4167 | 242 @node Comment Tips |
| 3294 | 243 @section Tips on Writing Comments |
| 244 | |
| 245 Here are the conventions to follow when writing comments. | |
| 246 | |
| 247 @table @samp | |
| 248 @item # | |
| 249 Comments that start with a single sharp-sign, @samp{#}, should all be | |
| 250 aligned to the same column on the right of the source code. Such | |
| 251 comments usually explain how the code on the same line does its job. In | |
| 252 the Emacs mode for Octave, the @kbd{M-;} (@code{indent-for-comment}) | |
| 253 command automatically inserts such a @samp{#} in the right place, or | |
| 254 aligns such a comment if it is already present. | |
| 255 | |
| 256 @item ## | |
| 7345 | 257 Comments that start with a double sharp-sign, @samp{##}, should be aligned to |
| 3294 | 258 the same level of indentation as the code. Such comments usually |
| 259 describe the purpose of the following lines or the state of the program | |
| 260 at that point. | |
| 261 @end table | |
| 262 | |
| 263 @noindent | |
| 264 The indentation commands of the Octave mode in Emacs, such as @kbd{M-;} | |
| 265 (@code{indent-for-comment}) and @kbd{TAB} (@code{octave-indent-line}) | |
| 266 automatically indent comments according to these conventions, | |
| 267 depending on the number of semicolons. @xref{Comments,, | |
| 268 Manipulating Comments, emacs, The GNU Emacs Manual}. | |
| 269 | |
| 4167 | 270 @node Function Headers |
| 3294 | 271 @section Conventional Headers for Octave Functions |
| 272 @cindex header comments | |
| 273 | |
| 274 Octave has conventions for using special comments in function files | |
| 275 to give information such as who wrote them. This section explains these | |
| 276 conventions. | |
| 277 | |
| 278 The top of the file should contain a copyright notice, followed by a | |
| 279 block of comments that can be used as the help text for the function. | |
| 280 Here is an example: | |
| 281 | |
| 282 @example | |
| 6778 | 283 ## Copyright (C) 1996, 1997, 2007 John W. Eaton |
| 3294 | 284 ## |
| 285 ## This file is part of Octave. | |
| 286 ## | |
| 287 ## Octave is free software; you can redistribute it and/or | |
| 288 ## modify it under the terms of the GNU General Public | |
| 289 ## License as published by the Free Software Foundation; | |
| 7081 | 290 ## either version 3 of the License, or (at your option) any |
| 291 ## later version. | |
| 3294 | 292 ## |
| 293 ## Octave is distributed in the hope that it will be useful, | |
| 294 ## but WITHOUT ANY WARRANTY; without even the implied | |
| 295 ## warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
| 296 ## PURPOSE. See the GNU General Public License for more | |
| 297 ## details. | |
| 298 ## | |
| 299 ## You should have received a copy of the GNU General Public | |
| 300 ## License along with Octave; see the file COPYING. If not, | |
| 7016 | 301 ## see <http://www.gnu.org/licenses/>. |
| 3294 | 302 |
| 303 ## usage: [IN, OUT, PID] = popen2 (COMMAND, ARGS) | |
| 304 ## | |
| 305 ## Start a subprocess with two-way communication. COMMAND | |
| 306 ## specifies the name of the command to start. ARGS is an | |
| 307 ## array of strings containing options for COMMAND. IN and | |
| 308 ## OUT are the file ids of the input and streams for the | |
| 309 ## subprocess, and PID is the process id of the subprocess, | |
| 310 ## or -1 if COMMAND could not be executed. | |
| 311 ## | |
| 312 ## Example: | |
| 313 ## | |
| 314 ## [in, out, pid] = popen2 ("sort", "-nr"); | |
| 315 ## fputs (in, "these\nare\nsome\nstrings\n"); | |
| 316 ## fclose (in); | |
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317 ## while (ischar (s = fgets (out))) |
| 3294 | 318 ## fputs (stdout, s); |
| 319 ## endwhile | |
| 320 ## fclose (out); | |
| 321 @end example | |
| 322 | |
| 323 Octave uses the first block of comments in a function file that do not | |
| 324 appear to be a copyright notice as the help text for the file. For | |
| 325 Octave to recognize the first comment block as a copyright notice, it | |
| 6530 | 326 must start with the word `Copyright' after stripping the leading |
| 327 comment characters. | |
| 3294 | 328 |
| 329 After the copyright notice and help text come several @dfn{header | |
| 330 comment} lines, each beginning with @samp{## @var{header-name}:}. For | |
| 331 example, | |
| 332 | |
| 333 @example | |
| 334 @group | |
| 335 ## Author: jwe | |
| 336 ## Keywords: subprocesses input-output | |
| 337 ## Maintainer: jwe | |
| 338 @end group | |
| 339 @end example | |
| 340 | |
| 341 Here is a table of the conventional possibilities for @var{header-name}: | |
| 342 | |
| 343 @table @samp | |
| 344 @item Author | |
| 345 This line states the name and net address of at least the principal | |
| 346 author of the library. | |
| 347 | |
| 6670 | 348 @example |
| 9322 | 349 ## Author: John W. Eaton <jwe@@octave.org> |
| 6670 | 350 @end example |
| 3294 | 351 |
| 352 @item Maintainer | |
| 353 This line should contain a single name/address as in the Author line, or | |
| 354 an address only, or the string @samp{jwe}. If there is no maintainer | |
| 355 line, the person(s) in the Author field are presumed to be the | |
| 356 maintainers. The example above is mildly bogus because the maintainer | |
| 357 line is redundant. | |
| 358 | |
| 359 The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
| 360 possible a function to ``send mail to the maintainer'' without | |
| 361 having to mine the name out by hand. | |
| 362 | |
| 363 Be sure to surround the network address with @samp{<@dots{}>} if | |
| 364 you include the person's full name as well as the network address. | |
| 365 | |
| 366 @item Created | |
| 367 This optional line gives the original creation date of the | |
| 368 file. For historical interest only. | |
| 369 | |
| 370 @item Version | |
| 371 If you wish to record version numbers for the individual Octave program, | |
| 372 put them in this line. | |
| 373 | |
| 374 @item Adapted-By | |
| 375 In this header line, place the name of the person who adapted the | |
| 376 library for installation (to make it fit the style conventions, for | |
| 377 example). | |
| 378 | |
| 379 @item Keywords | |
| 380 This line lists keywords. Eventually, it will be used by an apropos | |
| 381 command to allow people will find your package when they're looking for | |
| 382 things by topic area. To separate the keywords, you can use spaces, | |
| 383 commas, or both. | |
| 384 @end table | |
| 385 | |
| 386 Just about every Octave function ought to have the @samp{Author} and | |
| 387 @samp{Keywords} header comment lines. Use the others if they are | |
| 388 appropriate. You can also put in header lines with other header | |
| 389 names---they have no standard meanings, so they can't do any harm. | |
| 6574 | 390 |
| 391 @node Documentation Tips | |
| 392 @section Tips for Documentation Strings | |
| 393 | |
| 394 As noted above, documentation is typically in a commented header block | |
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395 on an Octave function following the copyright statement. The help string |
| 7001 | 396 shown above is an unformatted string and will be displayed as is by |
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397 Octave. Here are some tips for the writing of documentation strings. |
| 6574 | 398 |
| 399 @itemize @bullet | |
| 400 @item | |
| 401 Every command, function, or variable intended for users to know about | |
| 402 should have a documentation string. | |
| 403 | |
| 404 @item | |
| 405 An internal variable or subroutine of an Octave program might as well have | |
| 406 a documentation string. | |
| 407 | |
| 408 @item | |
| 409 The first line of the documentation string should consist of one or two | |
| 410 complete sentences that stand on their own as a summary. | |
| 411 | |
| 412 The documentation string can have additional lines that expand on the | |
| 413 details of how to use the function or variable. The additional lines | |
| 414 should also be made up of complete sentences. | |
| 415 | |
| 416 @item | |
| 417 For consistency, phrase the verb in the first sentence of a | |
| 418 documentation string as an infinitive with ``to'' omitted. For | |
| 419 instance, use ``Return the frob of A and B.'' in preference to ``Returns | |
| 420 the frob of A and B@.'' Usually it looks good to do likewise for the | |
| 421 rest of the first paragraph. Subsequent paragraphs usually look better | |
| 422 if they have proper subjects. | |
| 423 | |
| 424 @item | |
| 425 Write documentation strings in the active voice, not the passive, and in | |
| 426 the present tense, not the future. For instance, use ``Return a list | |
| 427 containing A and B.'' instead of ``A list containing A and B will be | |
| 428 returned.'' | |
| 429 | |
| 430 @item | |
| 431 Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
| 432 Instead of, ``Cause Octave to display text in boldface,'' write just | |
| 433 ``Display text in boldface.'' | |
| 434 | |
| 435 @item | |
| 436 Do not start or end a documentation string with whitespace. | |
| 437 | |
| 438 @item | |
| 439 Format the documentation string so that it fits in an Emacs window on an | |
| 440 80-column screen. It is a good idea for most lines to be no wider than | |
| 441 60 characters. | |
| 442 | |
| 443 However, rather than simply filling the entire documentation string, you | |
| 444 can make it much more readable by choosing line breaks with care. | |
| 445 Use blank lines between topics if the documentation string is long. | |
| 446 | |
| 447 @item | |
| 448 @strong{Do not} indent subsequent lines of a documentation string so | |
| 449 that the text is lined up in the source code with the text of the first | |
| 450 line. This looks nice in the source code, but looks bizarre when users | |
| 451 view the documentation. Remember that the indentation before the | |
| 452 starting double-quote is not part of the string! | |
| 453 | |
| 454 @item | |
| 455 The documentation string for a variable that is a yes-or-no flag should | |
| 456 start with words such as ``Nonzero means@dots{}'', to make it clear that | |
| 457 all nonzero values are equivalent and indicate explicitly what zero and | |
| 458 nonzero mean. | |
| 459 | |
| 460 @item | |
| 461 When a function's documentation string mentions the value of an argument | |
| 462 of the function, use the argument name in capital letters as if it were | |
| 463 a name for that value. Thus, the documentation string of the operator | |
| 464 @code{/} refers to its second argument as @samp{DIVISOR}, because the | |
| 465 actual argument name is @code{divisor}. | |
| 466 | |
| 467 Also use all caps for meta-syntactic variables, such as when you show | |
| 468 the decomposition of a list or vector into subunits, some of which may | |
| 469 vary. | |
| 470 @end itemize | |
| 471 | |
| 472 Octave also allows extensive formatting of the help string of functions | |
| 473 using Texinfo. The effect on the online documentation is relatively | |
| 474 small, but makes the help string of functions conform to the help of | |
| 475 Octave's own functions. However, the effect on the appearance of printed | |
| 476 or online documentation will be greatly improved. | |
| 477 | |
| 478 The fundamental building block of Texinfo documentation strings is the | |
| 479 Texinfo-macro @code{@@deftypefn}, which takes three arguments: The class | |
| 480 the function is in, its output arguments, and the function's | |
| 481 signature. Typical classes for functions include @code{Function File} | |
| 482 for standard Octave functions, and @code{Loadable Function} for | |
| 483 dynamically linked functions. A skeletal Texinfo documentation string | |
| 484 therefore looks like this | |
| 485 | |
| 486 @example | |
| 487 @group | |
| 488 -*- texinfo -*- | |
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489 @@deftypefn@{Function File@} @{@@var@{ret@} =@} fn (@dots{}) |
| 6574 | 490 @@cindex index term |
| 7081 | 491 Help text in Texinfo format. Code samples should be marked |
| 492 like @@code@{sample of code@} and variables should be marked | |
| 493 as @@var@{variable@}. | |
| 494 @@seealso@{fn2@} | |
| 6574 | 495 @@end deftypefn |
| 496 @end group | |
| 497 @end example | |
| 498 | |
| 499 This help string must be commented in user functions, or in the help | |
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500 string of the @w{@code{DEFUN_DLD}} macro for dynamically loadable |
| 6574 | 501 functions. The important aspects of the documentation string are |
| 502 | |
| 503 @table @asis | |
| 504 @item -*- texinfo -*- | |
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505 This string signals Octave that the following text is in Texinfo format, |
| 6574 | 506 and should be the first part of any help string in Texinfo format. |
| 507 @item @@deftypefn@{class@} @dots{} @@end deftypefn | |
| 508 The entire help string should be enclosed within the block defined by | |
| 509 deftypefn. | |
| 510 @item @@cindex index term | |
| 511 This generates an index entry, and can be useful when the function is | |
| 512 included as part of a larger piece of documentation. It is ignored | |
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513 within Octave's help viewer. Only one index term may appear per line |
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514 but multiple @@cindex lines are valid if the function should be |
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515 filed under different terms. |
| 6574 | 516 @item @@var@{variable@} |
| 517 All variables should be marked with this macro. The markup of variables | |
| 518 is then changed appropriately for display. | |
| 519 @item @@code@{sample of code@} | |
| 520 All samples of code should be marked with this macro for the same | |
| 521 reasons as the @@var macro. | |
| 522 @item @@seealso@{function2@} | |
| 523 This is a comma separated list of function names that allows cross | |
| 524 referencing from one function documentation string to another. | |
| 525 @end table | |
| 526 | |
| 527 Texinfo format has been designed to generate output for online viewing | |
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528 with text terminals as well as generating high-quality printed output. |
| 6574 | 529 To these ends, Texinfo has commands which control the diversion of parts |
| 530 of the document into a particular output processor. Three formats are | |
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531 of importance: info, html and @TeX{}. These are selected with |
| 6574 | 532 |
| 533 @example | |
| 534 @group | |
| 535 @@ifinfo | |
| 536 Text area for info only | |
| 537 @@end ifinfo | |
| 538 @end group | |
| 539 @end example | |
| 540 | |
| 541 @example | |
| 542 @group | |
| 543 @@ifhtml | |
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544 Text area for HTML only |
| 6574 | 545 @@end ifhtml |
| 546 @end group | |
| 547 @end example | |
| 548 | |
| 549 @example | |
| 550 @group | |
| 551 @@tex | |
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552 Text area for TeX only |
| 6574 | 553 @@end tex |
| 554 @end group | |
| 555 @end example | |
| 556 | |
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557 Note that often @TeX{} output can be used in html documents and so often |
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558 the @code{@@ifhtml} blocks are unnecessary. If no specific output |
| 6574 | 559 processor is chosen, by default, the text goes into all output |
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560 processors. It is usual to have the above blocks in pairs to allow the |
| 6574 | 561 same information to be conveyed in all output formats, but with a |
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562 different markup. Currently, most Octave documentation only makes a |
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563 distinction between @TeX{} and all other formats. Therefore, the |
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564 following construct is seen repeatedly. |
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565 |
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566 @example |
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567 @group |
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568 @@tex |
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569 text for TeX only |
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570 @@end tex |
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571 @@ifnottex |
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572 text for info, HTML, plaintext |
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573 @@end ifnottex |
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574 @end group |
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575 @end example |
| 6574 | 576 |
| 577 Another important feature of Texinfo that is often used in Octave help | |
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578 strings is the @code{@@example} environment. An example of its use is |
| 6574 | 579 |
| 580 @example | |
| 581 @group | |
| 582 @@example | |
| 583 @@group | |
| 584 @@code@{2 * 2@} | |
| 585 @@result@{@} 4 | |
| 586 @@end group | |
| 587 @@end example | |
| 588 @end group | |
| 589 @end example | |
| 590 | |
| 591 which produces | |
| 592 | |
| 593 @example | |
| 594 @group | |
| 595 @code{2 * 2} | |
| 596 @result{} 4 | |
| 597 @end group | |
| 598 @end example | |
| 599 | |
| 600 The @code{@@group} block prevents the example from being split across a | |
| 601 page boundary, while the @code{@@result@{@}} macro produces a right | |
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602 arrow signifying the result of a command. If your example is larger than |
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603 20 lines it is better NOT to use grouping so that a reasonable page boundary |
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604 can be calculated. |
| 6574 | 605 |
| 8828 | 606 In many cases a function has multiple ways in which it can be called, |
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607 and the @code{@@deftypefnx} macro can be used to give alternatives. For |
| 6574 | 608 example |
| 609 | |
| 610 @example | |
| 611 @group | |
| 612 -*- texinfo -*- | |
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613 @@deftypefn@{Function File@} @{@@var@{a@} =@} fn (@@var@{x@}, @dots{}) |
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614 @@deftypefnx@{Function File@} @{@@var@{a@} =@} fn (@@var@{y@}, @dots{}) |
| 6574 | 615 Help text in Texinfo format. |
| 616 @@end deftypefn | |
| 617 @end group | |
| 618 @end example | |
| 619 | |
| 620 Many complete examples of Texinfo documentation can be taken from the | |
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621 help strings for the Octave functions themselves. A relatively complete |
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622 example of which is the @code{nchoosek} function. The Texinfo |
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623 documentation string for @code{nchoosek} is |
| 6574 | 624 |
| 625 @example | |
| 626 -*- texinfo -*- | |
| 7081 | 627 @@deftypefn @{Function File@} @{@} nchoosek (@@var@{n@}, @@var@{k@}) |
| 6574 | 628 |
| 7081 | 629 Compute the binomial coefficient or all combinations of |
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630 @@var@{n@}. If @@var@{n@} is a scalar then, calculate the |
| 7081 | 631 binomial coefficient of @@var@{n@} and @@var@{k@}, defined as |
| 6574 | 632 |
| 633 @@tex | |
| 634 $$ | |
| 635 @{n \choose k@} = @{n (n-1) (n-2) \cdots (n-k+1) \over k!@} | |
| 636 $$ | |
| 637 @@end tex | |
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638 @@ifnottex |
| 6574 | 639 |
| 640 @@example | |
| 641 @@group | |
| 642 / \ | |
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643 | n | n (n-1) (n-2) @dots{} (n-k+1) |
| 6574 | 644 | | = ------------------------- |
| 645 | k | k! | |
| 646 \ / | |
| 647 @@end group | |
| 648 @@end example | |
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649 @@end ifnottex |
| 6574 | 650 |
| 7081 | 651 If @@var@{n@} is a vector, this generates all combinations |
| 652 of the elements of @@var@{n@}, taken @@var@{k@} at a time, | |
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653 one row per combination. The resulting @@var@{c@} has size |
| 7081 | 654 @@code@{[nchoosek (length (@@var@{n@}),@@var@{k@}), @@var@{k@}]@}. |
| 6574 | 655 |
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656 @@code@{nchoosek@} works only for non-negative integer arguments; use |
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657 @@code@{bincoeff@} for non-integer scalar arguments and for using vector |
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658 arguments to compute many coefficients at once. |
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659 |
| 6574 | 660 @@seealso@{bincoeff@} |
| 661 @@end deftypefn | |
| 662 @end example | |
| 663 | |
| 664 which demonstrates most of the concepts discussed above. | |
| 665 @iftex | |
| 666 This documentation string renders as | |
| 667 | |
| 668 @c Note actually use the output of info below rather than try and | |
| 669 @c reproduce it here to prevent it looking different than how it would | |
| 670 @c appear with info. | |
| 671 @example | |
| 672 @group | |
| 673 -- Function File: C = nchoosek (N, K) | |
| 7081 | 674 Compute the binomial coefficient or all combinations |
| 675 of N. If N is a scalar then, calculate the binomial | |
| 676 coefficient of N and K, defined as | |
| 6574 | 677 |
| 678 / \ | |
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679 | n | n (n-1) (n-2) @dots{} (n-k+1) n! |
| 7081 | 680 | | = ------------------------- = --------- |
| 681 | k | k! k! (n-k)! | |
| 6574 | 682 \ / |
| 683 | |
| 7081 | 684 If N is a vector generate all combinations of the |
| 685 elements of N, taken K at a time, one row per | |
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686 combination. The resulting C has size `[nchoosek |
| 7081 | 687 (length (N), K), K]'. |
| 6574 | 688 |
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689 `nchoosek' works only for non-negative integer |
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690 arguments; use `bincoeff' for non-integer scalar |
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691 arguments and for using vector arguments to compute |
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692 many coefficients at once. |
| 6574 | 693 |
| 694 See also: bincoeff. | |
| 695 @end group | |
| 696 @end example | |
| 697 | |
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698 using info, whereas in a printed documentation using @TeX{} it will appear |
| 6574 | 699 as |
| 700 | |
| 701 @deftypefn {Function File} {@var{c} =} nchoosek (@var{n}, @var{k}) | |
| 702 | |
| 6576 | 703 Compute the binomial coefficient or all combinations of @var{n}. |
| 6574 | 704 If @var{n} is a scalar then, calculate the binomial coefficient |
| 705 of @var{n} and @var{k}, defined as | |
| 706 | |
| 707 @tex | |
| 708 $$ | |
| 709 {n \choose k} = {n (n-1) (n-2) \cdots (n-k+1) \over k!} | |
| 710 $$ | |
| 711 @end tex | |
| 712 | |
| 713 If @var{n} is a vector generate all combinations of the elements | |
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714 of @var{n}, taken @var{k} at a time, one row per combination. The |
| 6574 | 715 resulting @var{c} has size @code{[nchoosek (length (@var{n}), |
| 716 @var{k}), @var{k}]}. | |
| 717 | |
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718 @code{nchoosek} works only for non-negative integer arguments; use |
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719 @code{bincoeff} for non-integer scalar arguments and for using vector |
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720 arguments to compute many coefficients at once. |
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721 |
| 6574 | 722 @seealso{bincoeff} |
| 723 @end deftypefn | |
| 724 | |
| 725 @end iftex |