Mercurial > octave-nkf
annotate doc/interpreter/tips.txi @ 10812:5b68000faac1
tips update
| author | Jaroslav Hajek <highegg@gmail.com> |
|---|---|
| date | Wed, 21 Jul 2010 09:01:06 +0200 |
| parents | 3140cb7a05a1 |
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| rev | line source |
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| 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 | |
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88 Vectorize loops. For instance, rather than |
| 9356 | 89 @example |
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90 @group |
| 9356 | 91 for i = 1:n-1 |
| 92 a(i) = b(i+1) - b(i); | |
| 93 endfor | |
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94 @end group |
| 9356 | 95 @end example |
| 96 | |
| 97 write | |
| 98 | |
| 99 @example | |
| 100 a = b(2:n) - b(1:n-1); | |
| 101 @end example | |
| 102 | |
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103 This is especially important for loops with "cheap" bodies. Often it suffices to vectorize |
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104 just the innermost loop to get acceptable performance. A general rule of thumb is that the |
| 9356 | 105 "order" of the vectorized body should be greater or equal to the "order" of the enclosing loop. |
| 106 | |
| 107 @item | |
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108 Use built-in and library functions if possible. Built-in and compiled functions are very fast. |
| 9356 | 109 Even with a m-file library function, chances are good that it is already optimized, or will be |
| 110 optimized more in a future release. | |
| 111 | |
| 10812 | 112 For instance, even better than |
| 113 | |
| 114 @example | |
| 115 a = b(2:n) - b(1:n-1); | |
| 116 @end example | |
| 117 | |
| 118 is | |
| 119 | |
| 120 @example | |
| 121 a = diff (b); | |
| 122 @end example | |
| 123 | |
| 124 | |
| 9356 | 125 @item |
| 10812 | 126 Avoid computing costly intermediate results multiple times. Octave currently |
| 9356 | 127 does not eliminate common subexpressions. |
| 9486 | 128 Also, certain internal computation results are cached for variables. |
| 129 For instance, if a matrix variable is used multiple times as an index, | |
| 130 checking the indices (and internal conversion to integers) is only done once. | |
| 3294 | 131 |
| 132 @item | |
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133 Be aware of lazy copies (copy-on-write). When a copy of an object |
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134 is created, the data is not immediately copied, but rather shared. The actual |
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135 copying is postponed until the copied data needs to be modified. For example: |
| 9356 | 136 |
| 137 @example | |
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138 @group |
| 9356 | 139 a = zeros (1000); # create a 1000x1000 matrix |
| 140 b = a; # no copying done here | |
| 141 b(1) = 1; # copying done here | |
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142 @end group |
| 9356 | 143 @end example |
| 144 | |
| 145 Lazy copying applies to whole Octave objects such as matrices, cells, struct, | |
| 146 and also individual cell or struct elements (not array elements). | |
| 147 | |
| 148 Additionally, index expressions also use lazy copying when Octave can determine | |
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149 that the indexed portion is contiguous in memory. For example: |
| 9356 | 150 |
| 151 @example | |
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152 @group |
| 9356 | 153 a = zeros (1000); # create a 1000x1000 matrix |
| 154 b = a(:,10:100); # no copying done here | |
| 155 b = a(10:100,:); # copying done here | |
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156 @end group |
| 9356 | 157 @end example |
| 158 | |
| 159 This applies to arrays (matrices), cell arrays, and structs indexed using (). | |
| 160 Index expressions generating cs-lists can also benefit of shallow copying | |
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161 in some cases. In particular, when @var{a} is a struct array, expressions like |
| 9356 | 162 @code{@{a.x@}, @{a(:,2).x@}} will use lazy copying, so that data can be shared |
| 163 between a struct array and a cell array. | |
| 164 | |
| 165 Most indexing expressions do not live longer than their `parent' objects. | |
| 166 In rare cases, however, a lazily copied slice outlasts its parent, in which | |
| 167 case it becomes orphaned, still occupying unnecessarily more memory than needed. | |
| 168 To provide a remedy working in most real cases, | |
| 169 Octave checks for orphaned lazy slices at certain situations, when a value | |
| 170 is stored into a "permanent" location, such as a named variable or cell or | |
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171 struct element, and possibly economizes them. For example |
| 9356 | 172 |
| 173 @example | |
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174 @group |
| 9356 | 175 a = zeros (1000); # create a 1000x1000 matrix |
| 176 b = a(:,10:100); # lazy slice | |
| 177 a = []; # the original a array is still allocated | |
| 178 c@{1@} = b; # b is reallocated at this point | |
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179 @end group |
| 9356 | 180 @end example |
| 3294 | 181 |
| 182 @item | |
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183 Avoid deep recursion. Function calls to m-file functions carry a relatively significant overhead, |
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184 so rewriting a recursion as a loop often helps. Also, note that the maximum level of recursion is |
| 9356 | 185 limited. |
| 186 | |
| 187 @item | |
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188 Avoid resizing matrices unnecessarily. When building a single result |
| 3294 | 189 matrix from a series of calculations, set the size of the result matrix |
| 190 first, then insert values into it. Write | |
| 191 | |
| 192 @example | |
| 193 @group | |
| 194 result = zeros (big_n, big_m) | |
| 195 for i = over:and_over | |
| 196 r1 = @dots{} | |
| 197 r2 = @dots{} | |
| 198 result (r1, r2) = new_value (); | |
| 199 endfor | |
| 200 @end group | |
| 201 @end example | |
| 202 | |
| 203 @noindent | |
| 204 instead of | |
| 205 | |
| 206 @example | |
| 207 @group | |
| 208 result = []; | |
| 209 for i = ever:and_ever | |
| 210 result = [ result, new_value() ]; | |
| 211 endfor | |
| 212 @end group | |
| 213 @end example | |
| 214 | |
| 9356 | 215 Sometimes the number of items can't be computed in advance, and stack-like operations |
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216 are needed. When elements are being repeatedly inserted at/removed from the end of an |
| 9356 | 217 array, Octave detects it as stack usage and attempts to use a smarter memory management |
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218 strategy pre-allocating the array in bigger chunks. Likewise works for cell and |
| 9356 | 219 struct arrays. |
| 220 | |
| 221 @example | |
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222 @group |
| 9356 | 223 a = []; |
| 224 while (condition) | |
| 225 @dots{} | |
| 226 a(end+1) = value; # "push" operation | |
| 227 @dots{} | |
| 228 a(end) = []; # "pop" operation | |
| 229 @dots{} | |
| 230 endwhile | |
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231 @end group |
| 9356 | 232 @end example |
| 233 | |
| 3294 | 234 @item |
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235 Use @code{cellfun} intelligently. The @code{cellfun} function is a useful tool |
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236 for avoiding loops. @xref{Processing Data in Cell Arrays}. |
| 10284 | 237 @code{cellfun} is often used with anonymous function handles; however, calling |
| 9356 | 238 an anonymous function involves an overhead quite comparable to the overhead |
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239 of an m-file function. Passing a handle to a built-in function is faster, |
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240 because the interpreter is not involved in the internal loop. For example: |
| 9356 | 241 |
| 242 @example | |
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243 @group |
| 9356 | 244 a = @{@dots{}@} |
| 245 v = cellfun (@@(x) det(x), a); # compute determinants | |
| 246 v = cellfun (@@det, a); # faster | |
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247 @end group |
| 9356 | 248 @end example |
| 249 | |
| 250 @item | |
| 10284 | 251 Octave includes a number of other functions that can replace common types of loops, |
| 252 including @code{bsxfun}, @code{arrayfun}, @code{structfun}, @code{accumarray}. | |
| 253 These functions can take an arbitrary function as a handle. | |
| 10812 | 254 Be sure to get familiar with them if you want to become an Octave expert. |
| 10284 | 255 |
| 256 @item | |
| 9356 | 257 Avoid calling @code{eval} or @code{feval} excessively, because |
| 3294 | 258 they require Octave to parse input or look up the name of a function in |
| 259 the symbol table. | |
| 260 | |
| 261 If you are using @code{eval} as an exception handling mechanism and not | |
| 262 because you need to execute some arbitrary text, use the @code{try} | |
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263 statement instead. @xref{The @code{try} Statement}. |
| 3294 | 264 |
| 265 @item | |
| 266 If you are calling lots of functions but none of them will need to | |
| 267 change during your run, set the variable | |
| 268 @code{ignore_function_time_stamp} to @code{"all"} so that Octave doesn't | |
| 269 waste a lot of time checking to see if you have updated your function | |
| 270 files. | |
| 271 @end itemize | |
| 272 | |
| 4167 | 273 @node Comment Tips |
| 3294 | 274 @section Tips on Writing Comments |
| 275 | |
| 276 Here are the conventions to follow when writing comments. | |
| 277 | |
| 278 @table @samp | |
| 279 @item # | |
| 280 Comments that start with a single sharp-sign, @samp{#}, should all be | |
| 281 aligned to the same column on the right of the source code. Such | |
| 282 comments usually explain how the code on the same line does its job. In | |
| 283 the Emacs mode for Octave, the @kbd{M-;} (@code{indent-for-comment}) | |
| 284 command automatically inserts such a @samp{#} in the right place, or | |
| 285 aligns such a comment if it is already present. | |
| 286 | |
| 287 @item ## | |
| 7345 | 288 Comments that start with a double sharp-sign, @samp{##}, should be aligned to |
| 3294 | 289 the same level of indentation as the code. Such comments usually |
| 290 describe the purpose of the following lines or the state of the program | |
| 291 at that point. | |
| 292 @end table | |
| 293 | |
| 294 @noindent | |
| 295 The indentation commands of the Octave mode in Emacs, such as @kbd{M-;} | |
| 296 (@code{indent-for-comment}) and @kbd{TAB} (@code{octave-indent-line}) | |
| 297 automatically indent comments according to these conventions, | |
| 298 depending on the number of semicolons. @xref{Comments,, | |
| 299 Manipulating Comments, emacs, The GNU Emacs Manual}. | |
| 300 | |
| 4167 | 301 @node Function Headers |
| 3294 | 302 @section Conventional Headers for Octave Functions |
| 303 @cindex header comments | |
| 304 | |
| 305 Octave has conventions for using special comments in function files | |
| 306 to give information such as who wrote them. This section explains these | |
| 307 conventions. | |
| 308 | |
| 309 The top of the file should contain a copyright notice, followed by a | |
| 310 block of comments that can be used as the help text for the function. | |
| 311 Here is an example: | |
| 312 | |
| 313 @example | |
| 6778 | 314 ## Copyright (C) 1996, 1997, 2007 John W. Eaton |
| 3294 | 315 ## |
| 316 ## This file is part of Octave. | |
| 317 ## | |
| 318 ## Octave is free software; you can redistribute it and/or | |
| 319 ## modify it under the terms of the GNU General Public | |
| 320 ## License as published by the Free Software Foundation; | |
| 7081 | 321 ## either version 3 of the License, or (at your option) any |
| 322 ## later version. | |
| 3294 | 323 ## |
| 324 ## Octave is distributed in the hope that it will be useful, | |
| 325 ## but WITHOUT ANY WARRANTY; without even the implied | |
| 326 ## warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
| 327 ## PURPOSE. See the GNU General Public License for more | |
| 328 ## details. | |
| 329 ## | |
| 330 ## You should have received a copy of the GNU General Public | |
| 331 ## License along with Octave; see the file COPYING. If not, | |
| 7016 | 332 ## see <http://www.gnu.org/licenses/>. |
| 3294 | 333 |
| 334 ## usage: [IN, OUT, PID] = popen2 (COMMAND, ARGS) | |
| 335 ## | |
| 336 ## Start a subprocess with two-way communication. COMMAND | |
| 337 ## specifies the name of the command to start. ARGS is an | |
| 338 ## array of strings containing options for COMMAND. IN and | |
| 339 ## OUT are the file ids of the input and streams for the | |
| 340 ## subprocess, and PID is the process id of the subprocess, | |
| 341 ## or -1 if COMMAND could not be executed. | |
| 342 ## | |
| 343 ## Example: | |
| 344 ## | |
| 345 ## [in, out, pid] = popen2 ("sort", "-nr"); | |
| 346 ## fputs (in, "these\nare\nsome\nstrings\n"); | |
| 347 ## fclose (in); | |
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348 ## while (ischar (s = fgets (out))) |
| 3294 | 349 ## fputs (stdout, s); |
| 350 ## endwhile | |
| 351 ## fclose (out); | |
| 352 @end example | |
| 353 | |
| 354 Octave uses the first block of comments in a function file that do not | |
| 355 appear to be a copyright notice as the help text for the file. For | |
| 356 Octave to recognize the first comment block as a copyright notice, it | |
| 6530 | 357 must start with the word `Copyright' after stripping the leading |
| 358 comment characters. | |
| 3294 | 359 |
| 360 After the copyright notice and help text come several @dfn{header | |
| 361 comment} lines, each beginning with @samp{## @var{header-name}:}. For | |
| 362 example, | |
| 363 | |
| 364 @example | |
| 365 @group | |
| 366 ## Author: jwe | |
| 367 ## Keywords: subprocesses input-output | |
| 368 ## Maintainer: jwe | |
| 369 @end group | |
| 370 @end example | |
| 371 | |
| 372 Here is a table of the conventional possibilities for @var{header-name}: | |
| 373 | |
| 374 @table @samp | |
| 375 @item Author | |
| 376 This line states the name and net address of at least the principal | |
| 377 author of the library. | |
| 378 | |
| 6670 | 379 @example |
| 9322 | 380 ## Author: John W. Eaton <jwe@@octave.org> |
| 6670 | 381 @end example |
| 3294 | 382 |
| 383 @item Maintainer | |
| 384 This line should contain a single name/address as in the Author line, or | |
| 385 an address only, or the string @samp{jwe}. If there is no maintainer | |
| 386 line, the person(s) in the Author field are presumed to be the | |
| 387 maintainers. The example above is mildly bogus because the maintainer | |
| 388 line is redundant. | |
| 389 | |
| 390 The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
| 391 possible a function to ``send mail to the maintainer'' without | |
| 392 having to mine the name out by hand. | |
| 393 | |
| 394 Be sure to surround the network address with @samp{<@dots{}>} if | |
| 395 you include the person's full name as well as the network address. | |
| 396 | |
| 397 @item Created | |
| 398 This optional line gives the original creation date of the | |
| 399 file. For historical interest only. | |
| 400 | |
| 401 @item Version | |
| 402 If you wish to record version numbers for the individual Octave program, | |
| 403 put them in this line. | |
| 404 | |
| 405 @item Adapted-By | |
| 406 In this header line, place the name of the person who adapted the | |
| 407 library for installation (to make it fit the style conventions, for | |
| 408 example). | |
| 409 | |
| 410 @item Keywords | |
| 411 This line lists keywords. Eventually, it will be used by an apropos | |
| 412 command to allow people will find your package when they're looking for | |
| 413 things by topic area. To separate the keywords, you can use spaces, | |
| 414 commas, or both. | |
| 415 @end table | |
| 416 | |
| 417 Just about every Octave function ought to have the @samp{Author} and | |
| 418 @samp{Keywords} header comment lines. Use the others if they are | |
| 419 appropriate. You can also put in header lines with other header | |
| 420 names---they have no standard meanings, so they can't do any harm. | |
| 6574 | 421 |
| 422 @node Documentation Tips | |
| 423 @section Tips for Documentation Strings | |
| 424 | |
| 425 As noted above, documentation is typically in a commented header block | |
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426 on an Octave function following the copyright statement. The help string |
| 7001 | 427 shown above is an unformatted string and will be displayed as is by |
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428 Octave. Here are some tips for the writing of documentation strings. |
| 6574 | 429 |
| 430 @itemize @bullet | |
| 431 @item | |
| 432 Every command, function, or variable intended for users to know about | |
| 433 should have a documentation string. | |
| 434 | |
| 435 @item | |
| 436 An internal variable or subroutine of an Octave program might as well have | |
| 437 a documentation string. | |
| 438 | |
| 439 @item | |
| 440 The first line of the documentation string should consist of one or two | |
| 441 complete sentences that stand on their own as a summary. | |
| 442 | |
| 443 The documentation string can have additional lines that expand on the | |
| 444 details of how to use the function or variable. The additional lines | |
| 445 should also be made up of complete sentences. | |
| 446 | |
| 447 @item | |
| 448 For consistency, phrase the verb in the first sentence of a | |
| 449 documentation string as an infinitive with ``to'' omitted. For | |
| 450 instance, use ``Return the frob of A and B.'' in preference to ``Returns | |
| 451 the frob of A and B@.'' Usually it looks good to do likewise for the | |
| 452 rest of the first paragraph. Subsequent paragraphs usually look better | |
| 453 if they have proper subjects. | |
| 454 | |
| 455 @item | |
| 456 Write documentation strings in the active voice, not the passive, and in | |
| 457 the present tense, not the future. For instance, use ``Return a list | |
| 458 containing A and B.'' instead of ``A list containing A and B will be | |
| 459 returned.'' | |
| 460 | |
| 461 @item | |
| 462 Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
| 463 Instead of, ``Cause Octave to display text in boldface,'' write just | |
| 464 ``Display text in boldface.'' | |
| 465 | |
| 466 @item | |
| 467 Do not start or end a documentation string with whitespace. | |
| 468 | |
| 469 @item | |
| 470 Format the documentation string so that it fits in an Emacs window on an | |
| 471 80-column screen. It is a good idea for most lines to be no wider than | |
| 472 60 characters. | |
| 473 | |
| 474 However, rather than simply filling the entire documentation string, you | |
| 475 can make it much more readable by choosing line breaks with care. | |
| 476 Use blank lines between topics if the documentation string is long. | |
| 477 | |
| 478 @item | |
| 479 @strong{Do not} indent subsequent lines of a documentation string so | |
| 480 that the text is lined up in the source code with the text of the first | |
| 481 line. This looks nice in the source code, but looks bizarre when users | |
| 482 view the documentation. Remember that the indentation before the | |
| 483 starting double-quote is not part of the string! | |
| 484 | |
| 485 @item | |
| 486 The documentation string for a variable that is a yes-or-no flag should | |
| 487 start with words such as ``Nonzero means@dots{}'', to make it clear that | |
| 488 all nonzero values are equivalent and indicate explicitly what zero and | |
| 489 nonzero mean. | |
| 490 | |
| 491 @item | |
| 492 When a function's documentation string mentions the value of an argument | |
| 493 of the function, use the argument name in capital letters as if it were | |
| 494 a name for that value. Thus, the documentation string of the operator | |
| 495 @code{/} refers to its second argument as @samp{DIVISOR}, because the | |
| 496 actual argument name is @code{divisor}. | |
| 497 | |
| 498 Also use all caps for meta-syntactic variables, such as when you show | |
| 499 the decomposition of a list or vector into subunits, some of which may | |
| 500 vary. | |
| 501 @end itemize | |
| 502 | |
| 503 Octave also allows extensive formatting of the help string of functions | |
| 504 using Texinfo. The effect on the online documentation is relatively | |
| 505 small, but makes the help string of functions conform to the help of | |
| 506 Octave's own functions. However, the effect on the appearance of printed | |
| 507 or online documentation will be greatly improved. | |
| 508 | |
| 509 The fundamental building block of Texinfo documentation strings is the | |
| 510 Texinfo-macro @code{@@deftypefn}, which takes three arguments: The class | |
| 511 the function is in, its output arguments, and the function's | |
| 512 signature. Typical classes for functions include @code{Function File} | |
| 513 for standard Octave functions, and @code{Loadable Function} for | |
| 514 dynamically linked functions. A skeletal Texinfo documentation string | |
| 515 therefore looks like this | |
| 516 | |
| 517 @example | |
| 518 @group | |
| 519 -*- texinfo -*- | |
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520 @@deftypefn@{Function File@} @{@@var@{ret@} =@} fn (@dots{}) |
| 6574 | 521 @@cindex index term |
| 7081 | 522 Help text in Texinfo format. Code samples should be marked |
| 523 like @@code@{sample of code@} and variables should be marked | |
| 524 as @@var@{variable@}. | |
| 525 @@seealso@{fn2@} | |
| 6574 | 526 @@end deftypefn |
| 527 @end group | |
| 528 @end example | |
| 529 | |
| 530 This help string must be commented in user functions, or in the help | |
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531 string of the @w{@code{DEFUN_DLD}} macro for dynamically loadable |
| 6574 | 532 functions. The important aspects of the documentation string are |
| 533 | |
| 534 @table @asis | |
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535 @item -*- @nospell{texinfo} -*- |
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536 This string signals Octave that the following text is in Texinfo format, |
| 6574 | 537 and should be the first part of any help string in Texinfo format. |
| 538 @item @@deftypefn@{class@} @dots{} @@end deftypefn | |
| 539 The entire help string should be enclosed within the block defined by | |
| 540 deftypefn. | |
| 541 @item @@cindex index term | |
| 542 This generates an index entry, and can be useful when the function is | |
| 543 included as part of a larger piece of documentation. It is ignored | |
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544 within Octave's help viewer. Only one index term may appear per line |
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545 but multiple @@cindex lines are valid if the function should be |
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546 filed under different terms. |
| 6574 | 547 @item @@var@{variable@} |
| 548 All variables should be marked with this macro. The markup of variables | |
| 549 is then changed appropriately for display. | |
| 550 @item @@code@{sample of code@} | |
| 551 All samples of code should be marked with this macro for the same | |
| 552 reasons as the @@var macro. | |
| 553 @item @@seealso@{function2@} | |
| 554 This is a comma separated list of function names that allows cross | |
| 555 referencing from one function documentation string to another. | |
| 556 @end table | |
| 557 | |
| 558 Texinfo format has been designed to generate output for online viewing | |
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559 with text terminals as well as generating high-quality printed output. |
| 6574 | 560 To these ends, Texinfo has commands which control the diversion of parts |
| 561 of the document into a particular output processor. Three formats are | |
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562 of importance: info, HTML and @TeX{}. These are selected with |
| 6574 | 563 |
| 564 @example | |
| 565 @group | |
| 566 @@ifinfo | |
| 567 Text area for info only | |
| 568 @@end ifinfo | |
| 569 @end group | |
| 570 @end example | |
| 571 | |
| 572 @example | |
| 573 @group | |
| 574 @@ifhtml | |
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575 Text area for HTML only |
| 6574 | 576 @@end ifhtml |
| 577 @end group | |
| 578 @end example | |
| 579 | |
| 580 @example | |
| 581 @group | |
| 582 @@tex | |
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583 Text area for TeX only |
| 6574 | 584 @@end tex |
| 585 @end group | |
| 586 @end example | |
| 587 | |
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588 Note that often @TeX{} output can be used in HTML documents and so often |
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589 the @code{@@ifhtml} blocks are unnecessary. If no specific output |
| 6574 | 590 processor is chosen, by default, the text goes into all output |
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591 processors. It is usual to have the above blocks in pairs to allow the |
| 6574 | 592 same information to be conveyed in all output formats, but with a |
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593 different markup. Currently, most Octave documentation only makes a |
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594 distinction between @TeX{} and all other formats. Therefore, the |
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595 following construct is seen repeatedly. |
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596 |
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597 @example |
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598 @group |
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599 @@tex |
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600 text for TeX only |
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601 @@end tex |
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602 @@ifnottex |
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603 text for info, HTML, plaintext |
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604 @@end ifnottex |
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605 @end group |
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606 @end example |
| 6574 | 607 |
| 608 Another important feature of Texinfo that is often used in Octave help | |
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609 strings is the @code{@@example} environment. An example of its use is |
| 6574 | 610 |
| 611 @example | |
| 612 @group | |
| 613 @@example | |
| 614 @@group | |
| 615 @@code@{2 * 2@} | |
| 616 @@result@{@} 4 | |
| 617 @@end group | |
| 618 @@end example | |
| 619 @end group | |
| 620 @end example | |
| 621 | |
| 622 which produces | |
| 623 | |
| 624 @example | |
| 625 @group | |
| 626 @code{2 * 2} | |
| 627 @result{} 4 | |
| 628 @end group | |
| 629 @end example | |
| 630 | |
| 631 The @code{@@group} block prevents the example from being split across a | |
| 632 page boundary, while the @code{@@result@{@}} macro produces a right | |
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633 arrow signifying the result of a command. If your example is larger than |
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634 20 lines it is better NOT to use grouping so that a reasonable page boundary |
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635 can be calculated. |
| 6574 | 636 |
| 8828 | 637 In many cases a function has multiple ways in which it can be called, |
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638 and the @code{@@deftypefnx} macro can be used to give alternatives. For |
| 6574 | 639 example |
| 640 | |
| 641 @example | |
| 642 @group | |
| 643 -*- texinfo -*- | |
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644 @@deftypefn@{Function File@} @{@@var@{a@} =@} fn (@@var@{x@}, @dots{}) |
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645 @@deftypefnx@{Function File@} @{@@var@{a@} =@} fn (@@var@{y@}, @dots{}) |
| 6574 | 646 Help text in Texinfo format. |
| 647 @@end deftypefn | |
| 648 @end group | |
| 649 @end example | |
| 650 | |
| 651 Many complete examples of Texinfo documentation can be taken from the | |
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652 help strings for the Octave functions themselves. A relatively complete |
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653 example of which is the @code{nchoosek} function. The Texinfo |
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654 documentation string for @code{nchoosek} is |
| 6574 | 655 |
| 656 @example | |
| 657 -*- texinfo -*- | |
| 7081 | 658 @@deftypefn @{Function File@} @{@} nchoosek (@@var@{n@}, @@var@{k@}) |
| 6574 | 659 |
| 7081 | 660 Compute the binomial coefficient or all combinations of |
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661 @@var@{n@}. If @@var@{n@} is a scalar then, calculate the |
| 7081 | 662 binomial coefficient of @@var@{n@} and @@var@{k@}, defined as |
| 6574 | 663 |
| 664 @@tex | |
| 665 $$ | |
| 666 @{n \choose k@} = @{n (n-1) (n-2) \cdots (n-k+1) \over k!@} | |
| 667 $$ | |
| 668 @@end tex | |
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669 @@ifnottex |
| 6574 | 670 |
| 671 @@example | |
| 672 @@group | |
| 673 / \ | |
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674 | n | n (n-1) (n-2) @dots{} (n-k+1) |
| 6574 | 675 | | = ------------------------- |
| 676 | k | k! | |
| 677 \ / | |
| 678 @@end group | |
| 679 @@end example | |
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680 @@end ifnottex |
| 6574 | 681 |
| 7081 | 682 If @@var@{n@} is a vector, this generates all combinations |
| 683 of the elements of @@var@{n@}, taken @@var@{k@} at a time, | |
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684 one row per combination. The resulting @@var@{c@} has size |
| 7081 | 685 @@code@{[nchoosek (length (@@var@{n@}),@@var@{k@}), @@var@{k@}]@}. |
| 6574 | 686 |
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687 @@code@{nchoosek@} works only for non-negative integer arguments; use |
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688 @@code@{bincoeff@} for non-integer scalar arguments and for using vector |
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689 arguments to compute many coefficients at once. |
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690 |
| 6574 | 691 @@seealso@{bincoeff@} |
| 692 @@end deftypefn | |
| 693 @end example | |
| 694 | |
| 695 which demonstrates most of the concepts discussed above. | |
| 696 @iftex | |
| 697 This documentation string renders as | |
| 698 | |
| 699 @c Note actually use the output of info below rather than try and | |
| 700 @c reproduce it here to prevent it looking different than how it would | |
| 701 @c appear with info. | |
| 702 @example | |
| 703 @group | |
| 704 -- Function File: C = nchoosek (N, K) | |
| 7081 | 705 Compute the binomial coefficient or all combinations |
| 706 of N. If N is a scalar then, calculate the binomial | |
| 707 coefficient of N and K, defined as | |
| 6574 | 708 |
| 709 / \ | |
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710 | n | n (n-1) (n-2) @dots{} (n-k+1) n! |
| 7081 | 711 | | = ------------------------- = --------- |
| 712 | k | k! k! (n-k)! | |
| 6574 | 713 \ / |
| 714 | |
| 7081 | 715 If N is a vector generate all combinations of the |
| 716 elements of N, taken K at a time, one row per | |
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717 combination. The resulting C has size `[nchoosek |
| 7081 | 718 (length (N), K), K]'. |
| 6574 | 719 |
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720 `nchoosek' works only for non-negative integer |
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721 arguments; use `bincoeff' for non-integer scalar |
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722 arguments and for using vector arguments to compute |
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723 many coefficients at once. |
| 6574 | 724 |
| 725 See also: bincoeff. | |
| 726 @end group | |
| 727 @end example | |
| 728 | |
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729 using info, whereas in a printed documentation using @TeX{} it will appear |
| 6574 | 730 as |
| 731 | |
| 732 @deftypefn {Function File} {@var{c} =} nchoosek (@var{n}, @var{k}) | |
| 733 | |
| 6576 | 734 Compute the binomial coefficient or all combinations of @var{n}. |
| 6574 | 735 If @var{n} is a scalar then, calculate the binomial coefficient |
| 736 of @var{n} and @var{k}, defined as | |
| 737 | |
| 738 @tex | |
| 739 $$ | |
| 740 {n \choose k} = {n (n-1) (n-2) \cdots (n-k+1) \over k!} | |
| 741 $$ | |
| 742 @end tex | |
| 743 | |
| 744 If @var{n} is a vector generate all combinations of the elements | |
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ec41eabf4499
Cleanup documentation files dynamic.texi, testfun.texi, tips.texi
Rik <rdrider0-list@yahoo.com>
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745 of @var{n}, taken @var{k} at a time, one row per combination. The |
| 6574 | 746 resulting @var{c} has size @code{[nchoosek (length (@var{n}), |
| 747 @var{k}), @var{k}]}. | |
| 748 | |
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9210
a7a9eecc07b5
Change recommendation for writing documentation to favor @tex
Rik <rdrider0-list@yahoo.com>
parents:
9209
diff
changeset
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749 @code{nchoosek} works only for non-negative integer arguments; use |
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a7a9eecc07b5
Change recommendation for writing documentation to favor @tex
Rik <rdrider0-list@yahoo.com>
parents:
9209
diff
changeset
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750 @code{bincoeff} for non-integer scalar arguments and for using vector |
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a7a9eecc07b5
Change recommendation for writing documentation to favor @tex
Rik <rdrider0-list@yahoo.com>
parents:
9209
diff
changeset
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751 arguments to compute many coefficients at once. |
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a7a9eecc07b5
Change recommendation for writing documentation to favor @tex
Rik <rdrider0-list@yahoo.com>
parents:
9209
diff
changeset
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752 |
| 6574 | 753 @seealso{bincoeff} |
| 754 @end deftypefn | |
| 755 | |
| 756 @end iftex |