Mercurial > octave-nkf
annotate doc/interpreter/tips.txi @ 11981:f69e27ff396a release-3-2-x
fix jwe email address
| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Thu, 11 Jun 2009 07:13:19 +0200 |
| parents | a7a9eecc07b5 |
| children | b2133f97079d |
| 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 | |
| 88 Avoid looping wherever possible. | |
| 89 | |
| 90 @item | |
| 91 Use iteration rather than recursion whenever possible. | |
| 92 Function calls are slow in Octave. | |
| 93 | |
| 94 @item | |
| 95 Avoid resizing matrices unnecessarily. When building a single result | |
| 96 matrix from a series of calculations, set the size of the result matrix | |
| 97 first, then insert values into it. Write | |
| 98 | |
| 99 @example | |
| 100 @group | |
| 101 result = zeros (big_n, big_m) | |
| 102 for i = over:and_over | |
| 103 r1 = @dots{} | |
| 104 r2 = @dots{} | |
| 105 result (r1, r2) = new_value (); | |
| 106 endfor | |
| 107 @end group | |
| 108 @end example | |
| 109 | |
| 110 @noindent | |
| 111 instead of | |
| 112 | |
| 113 @example | |
| 114 @group | |
| 115 result = []; | |
| 116 for i = ever:and_ever | |
| 117 result = [ result, new_value() ]; | |
| 118 endfor | |
| 119 @end group | |
| 120 @end example | |
| 121 | |
| 122 @item | |
| 123 Avoid calling @code{eval} or @code{feval} whenever possible, because | |
| 124 they require Octave to parse input or look up the name of a function in | |
| 125 the symbol table. | |
| 126 | |
| 127 If you are using @code{eval} as an exception handling mechanism and not | |
| 128 because you need to execute some arbitrary text, use the @code{try} | |
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129 statement instead. @xref{The @code{try} Statement}. |
| 3294 | 130 |
| 131 @item | |
| 132 If you are calling lots of functions but none of them will need to | |
| 133 change during your run, set the variable | |
| 134 @code{ignore_function_time_stamp} to @code{"all"} so that Octave doesn't | |
| 135 waste a lot of time checking to see if you have updated your function | |
| 136 files. | |
| 137 @end itemize | |
| 138 | |
| 4167 | 139 @node Comment Tips |
| 3294 | 140 @section Tips on Writing Comments |
| 141 | |
| 142 Here are the conventions to follow when writing comments. | |
| 143 | |
| 144 @table @samp | |
| 145 @item # | |
| 146 Comments that start with a single sharp-sign, @samp{#}, should all be | |
| 147 aligned to the same column on the right of the source code. Such | |
| 148 comments usually explain how the code on the same line does its job. In | |
| 149 the Emacs mode for Octave, the @kbd{M-;} (@code{indent-for-comment}) | |
| 150 command automatically inserts such a @samp{#} in the right place, or | |
| 151 aligns such a comment if it is already present. | |
| 152 | |
| 153 @item ## | |
| 7345 | 154 Comments that start with a double sharp-sign, @samp{##}, should be aligned to |
| 3294 | 155 the same level of indentation as the code. Such comments usually |
| 156 describe the purpose of the following lines or the state of the program | |
| 157 at that point. | |
| 158 @end table | |
| 159 | |
| 160 @noindent | |
| 161 The indentation commands of the Octave mode in Emacs, such as @kbd{M-;} | |
| 162 (@code{indent-for-comment}) and @kbd{TAB} (@code{octave-indent-line}) | |
| 163 automatically indent comments according to these conventions, | |
| 164 depending on the number of semicolons. @xref{Comments,, | |
| 165 Manipulating Comments, emacs, The GNU Emacs Manual}. | |
| 166 | |
| 4167 | 167 @node Function Headers |
| 3294 | 168 @section Conventional Headers for Octave Functions |
| 169 @cindex header comments | |
| 170 | |
| 171 Octave has conventions for using special comments in function files | |
| 172 to give information such as who wrote them. This section explains these | |
| 173 conventions. | |
| 174 | |
| 175 The top of the file should contain a copyright notice, followed by a | |
| 176 block of comments that can be used as the help text for the function. | |
| 177 Here is an example: | |
| 178 | |
| 179 @example | |
| 6778 | 180 ## Copyright (C) 1996, 1997, 2007 John W. Eaton |
| 3294 | 181 ## |
| 182 ## This file is part of Octave. | |
| 183 ## | |
| 184 ## Octave is free software; you can redistribute it and/or | |
| 185 ## modify it under the terms of the GNU General Public | |
| 186 ## License as published by the Free Software Foundation; | |
| 7081 | 187 ## either version 3 of the License, or (at your option) any |
| 188 ## later version. | |
| 3294 | 189 ## |
| 190 ## Octave is distributed in the hope that it will be useful, | |
| 191 ## but WITHOUT ANY WARRANTY; without even the implied | |
| 192 ## warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
| 193 ## PURPOSE. See the GNU General Public License for more | |
| 194 ## details. | |
| 195 ## | |
| 196 ## You should have received a copy of the GNU General Public | |
| 197 ## License along with Octave; see the file COPYING. If not, | |
| 7016 | 198 ## see <http://www.gnu.org/licenses/>. |
| 3294 | 199 |
| 200 ## usage: [IN, OUT, PID] = popen2 (COMMAND, ARGS) | |
| 201 ## | |
| 202 ## Start a subprocess with two-way communication. COMMAND | |
| 203 ## specifies the name of the command to start. ARGS is an | |
| 204 ## array of strings containing options for COMMAND. IN and | |
| 205 ## OUT are the file ids of the input and streams for the | |
| 206 ## subprocess, and PID is the process id of the subprocess, | |
| 207 ## or -1 if COMMAND could not be executed. | |
| 208 ## | |
| 209 ## Example: | |
| 210 ## | |
| 211 ## [in, out, pid] = popen2 ("sort", "-nr"); | |
| 212 ## fputs (in, "these\nare\nsome\nstrings\n"); | |
| 213 ## fclose (in); | |
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214 ## while (ischar (s = fgets (out))) |
| 3294 | 215 ## fputs (stdout, s); |
| 216 ## endwhile | |
| 217 ## fclose (out); | |
| 218 @end example | |
| 219 | |
| 220 Octave uses the first block of comments in a function file that do not | |
| 221 appear to be a copyright notice as the help text for the file. For | |
| 222 Octave to recognize the first comment block as a copyright notice, it | |
| 6530 | 223 must start with the word `Copyright' after stripping the leading |
| 224 comment characters. | |
| 3294 | 225 |
| 226 After the copyright notice and help text come several @dfn{header | |
| 227 comment} lines, each beginning with @samp{## @var{header-name}:}. For | |
| 228 example, | |
| 229 | |
| 230 @example | |
| 231 @group | |
| 232 ## Author: jwe | |
| 233 ## Keywords: subprocesses input-output | |
| 234 ## Maintainer: jwe | |
| 235 @end group | |
| 236 @end example | |
| 237 | |
| 238 Here is a table of the conventional possibilities for @var{header-name}: | |
| 239 | |
| 240 @table @samp | |
| 241 @item Author | |
| 242 This line states the name and net address of at least the principal | |
| 243 author of the library. | |
| 244 | |
| 6670 | 245 @example |
| 11981 | 246 ## Author: John W. Eaton <jwe@@octave.org> |
| 6670 | 247 @end example |
| 3294 | 248 |
| 249 @item Maintainer | |
| 250 This line should contain a single name/address as in the Author line, or | |
| 251 an address only, or the string @samp{jwe}. If there is no maintainer | |
| 252 line, the person(s) in the Author field are presumed to be the | |
| 253 maintainers. The example above is mildly bogus because the maintainer | |
| 254 line is redundant. | |
| 255 | |
| 256 The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
| 257 possible a function to ``send mail to the maintainer'' without | |
| 258 having to mine the name out by hand. | |
| 259 | |
| 260 Be sure to surround the network address with @samp{<@dots{}>} if | |
| 261 you include the person's full name as well as the network address. | |
| 262 | |
| 263 @item Created | |
| 264 This optional line gives the original creation date of the | |
| 265 file. For historical interest only. | |
| 266 | |
| 267 @item Version | |
| 268 If you wish to record version numbers for the individual Octave program, | |
| 269 put them in this line. | |
| 270 | |
| 271 @item Adapted-By | |
| 272 In this header line, place the name of the person who adapted the | |
| 273 library for installation (to make it fit the style conventions, for | |
| 274 example). | |
| 275 | |
| 276 @item Keywords | |
| 277 This line lists keywords. Eventually, it will be used by an apropos | |
| 278 command to allow people will find your package when they're looking for | |
| 279 things by topic area. To separate the keywords, you can use spaces, | |
| 280 commas, or both. | |
| 281 @end table | |
| 282 | |
| 283 Just about every Octave function ought to have the @samp{Author} and | |
| 284 @samp{Keywords} header comment lines. Use the others if they are | |
| 285 appropriate. You can also put in header lines with other header | |
| 286 names---they have no standard meanings, so they can't do any harm. | |
| 6574 | 287 |
| 288 @node Documentation Tips | |
| 289 @section Tips for Documentation Strings | |
| 290 | |
| 291 As noted above, documentation is typically in a commented header block | |
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292 on an Octave function following the copyright statement. The help string |
| 7001 | 293 shown above is an unformatted string and will be displayed as is by |
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294 Octave. Here are some tips for the writing of documentation strings. |
| 6574 | 295 |
| 296 @itemize @bullet | |
| 297 @item | |
| 298 Every command, function, or variable intended for users to know about | |
| 299 should have a documentation string. | |
| 300 | |
| 301 @item | |
| 302 An internal variable or subroutine of an Octave program might as well have | |
| 303 a documentation string. | |
| 304 | |
| 305 @item | |
| 306 The first line of the documentation string should consist of one or two | |
| 307 complete sentences that stand on their own as a summary. | |
| 308 | |
| 309 The documentation string can have additional lines that expand on the | |
| 310 details of how to use the function or variable. The additional lines | |
| 311 should also be made up of complete sentences. | |
| 312 | |
| 313 @item | |
| 314 For consistency, phrase the verb in the first sentence of a | |
| 315 documentation string as an infinitive with ``to'' omitted. For | |
| 316 instance, use ``Return the frob of A and B.'' in preference to ``Returns | |
| 317 the frob of A and B@.'' Usually it looks good to do likewise for the | |
| 318 rest of the first paragraph. Subsequent paragraphs usually look better | |
| 319 if they have proper subjects. | |
| 320 | |
| 321 @item | |
| 322 Write documentation strings in the active voice, not the passive, and in | |
| 323 the present tense, not the future. For instance, use ``Return a list | |
| 324 containing A and B.'' instead of ``A list containing A and B will be | |
| 325 returned.'' | |
| 326 | |
| 327 @item | |
| 328 Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
| 329 Instead of, ``Cause Octave to display text in boldface,'' write just | |
| 330 ``Display text in boldface.'' | |
| 331 | |
| 332 @item | |
| 333 Do not start or end a documentation string with whitespace. | |
| 334 | |
| 335 @item | |
| 336 Format the documentation string so that it fits in an Emacs window on an | |
| 337 80-column screen. It is a good idea for most lines to be no wider than | |
| 338 60 characters. | |
| 339 | |
| 340 However, rather than simply filling the entire documentation string, you | |
| 341 can make it much more readable by choosing line breaks with care. | |
| 342 Use blank lines between topics if the documentation string is long. | |
| 343 | |
| 344 @item | |
| 345 @strong{Do not} indent subsequent lines of a documentation string so | |
| 346 that the text is lined up in the source code with the text of the first | |
| 347 line. This looks nice in the source code, but looks bizarre when users | |
| 348 view the documentation. Remember that the indentation before the | |
| 349 starting double-quote is not part of the string! | |
| 350 | |
| 351 @item | |
| 352 The documentation string for a variable that is a yes-or-no flag should | |
| 353 start with words such as ``Nonzero means@dots{}'', to make it clear that | |
| 354 all nonzero values are equivalent and indicate explicitly what zero and | |
| 355 nonzero mean. | |
| 356 | |
| 357 @item | |
| 358 When a function's documentation string mentions the value of an argument | |
| 359 of the function, use the argument name in capital letters as if it were | |
| 360 a name for that value. Thus, the documentation string of the operator | |
| 361 @code{/} refers to its second argument as @samp{DIVISOR}, because the | |
| 362 actual argument name is @code{divisor}. | |
| 363 | |
| 364 Also use all caps for meta-syntactic variables, such as when you show | |
| 365 the decomposition of a list or vector into subunits, some of which may | |
| 366 vary. | |
| 367 @end itemize | |
| 368 | |
| 369 Octave also allows extensive formatting of the help string of functions | |
| 370 using Texinfo. The effect on the online documentation is relatively | |
| 371 small, but makes the help string of functions conform to the help of | |
| 372 Octave's own functions. However, the effect on the appearance of printed | |
| 373 or online documentation will be greatly improved. | |
| 374 | |
| 375 The fundamental building block of Texinfo documentation strings is the | |
| 376 Texinfo-macro @code{@@deftypefn}, which takes three arguments: The class | |
| 377 the function is in, its output arguments, and the function's | |
| 378 signature. Typical classes for functions include @code{Function File} | |
| 379 for standard Octave functions, and @code{Loadable Function} for | |
| 380 dynamically linked functions. A skeletal Texinfo documentation string | |
| 381 therefore looks like this | |
| 382 | |
| 383 @example | |
| 384 @group | |
| 385 -*- texinfo -*- | |
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386 @@deftypefn@{Function File@} @{@@var@{ret@} =@} fn (@dots{}) |
| 6574 | 387 @@cindex index term |
| 7081 | 388 Help text in Texinfo format. Code samples should be marked |
| 389 like @@code@{sample of code@} and variables should be marked | |
| 390 as @@var@{variable@}. | |
| 391 @@seealso@{fn2@} | |
| 6574 | 392 @@end deftypefn |
| 393 @end group | |
| 394 @end example | |
| 395 | |
| 396 This help string must be commented in user functions, or in the help | |
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397 string of the @w{@code{DEFUN_DLD}} macro for dynamically loadable |
| 6574 | 398 functions. The important aspects of the documentation string are |
| 399 | |
| 400 @table @asis | |
| 401 @item -*- texinfo -*- | |
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402 This string signals Octave that the following text is in Texinfo format, |
| 6574 | 403 and should be the first part of any help string in Texinfo format. |
| 404 @item @@deftypefn@{class@} @dots{} @@end deftypefn | |
| 405 The entire help string should be enclosed within the block defined by | |
| 406 deftypefn. | |
| 407 @item @@cindex index term | |
| 408 This generates an index entry, and can be useful when the function is | |
| 409 included as part of a larger piece of documentation. It is ignored | |
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410 within Octave's help viewer. Only one index term may appear per line |
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411 but multiple @@cindex lines are valid if the function should be |
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412 filed under different terms. |
| 6574 | 413 @item @@var@{variable@} |
| 414 All variables should be marked with this macro. The markup of variables | |
| 415 is then changed appropriately for display. | |
| 416 @item @@code@{sample of code@} | |
| 417 All samples of code should be marked with this macro for the same | |
| 418 reasons as the @@var macro. | |
| 419 @item @@seealso@{function2@} | |
| 420 This is a comma separated list of function names that allows cross | |
| 421 referencing from one function documentation string to another. | |
| 422 @end table | |
| 423 | |
| 424 Texinfo format has been designed to generate output for online viewing | |
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425 with text terminals as well as generating high-quality printed output. |
| 6574 | 426 To these ends, Texinfo has commands which control the diversion of parts |
| 427 of the document into a particular output processor. Three formats are | |
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428 of importance: info, html and @TeX{}. These are selected with |
| 6574 | 429 |
| 430 @example | |
| 431 @group | |
| 432 @@ifinfo | |
| 433 Text area for info only | |
| 434 @@end ifinfo | |
| 435 @end group | |
| 436 @end example | |
| 437 | |
| 438 @example | |
| 439 @group | |
| 440 @@ifhtml | |
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441 Text area for HTML only |
| 6574 | 442 @@end ifhtml |
| 443 @end group | |
| 444 @end example | |
| 445 | |
| 446 @example | |
| 447 @group | |
| 448 @@tex | |
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449 Text area for TeX only |
| 6574 | 450 @@end tex |
| 451 @end group | |
| 452 @end example | |
| 453 | |
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454 Note that often @TeX{} output can be used in html documents and so often |
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455 the @code{@@ifhtml} blocks are unnecessary. If no specific output |
| 6574 | 456 processor is chosen, by default, the text goes into all output |
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457 processors. It is usual to have the above blocks in pairs to allow the |
| 6574 | 458 same information to be conveyed in all output formats, but with a |
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459 different markup. Currently, most Octave documentation only makes a |
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460 distinction between @TeX{} and all other formats. Therefore, the |
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461 following construct is seen repeatedly. |
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462 |
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463 @example |
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464 @group |
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465 @@tex |
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466 text for TeX only |
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467 @@end tex |
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468 @@ifnottex |
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469 text for info, HTML, plaintext |
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470 @@end ifnottex |
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471 @end group |
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472 @end example |
| 6574 | 473 |
| 474 Another important feature of Texinfo that is often used in Octave help | |
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475 strings is the @code{@@example} environment. An example of its use is |
| 6574 | 476 |
| 477 @example | |
| 478 @group | |
| 479 @@example | |
| 480 @@group | |
| 481 @@code@{2 * 2@} | |
| 482 @@result@{@} 4 | |
| 483 @@end group | |
| 484 @@end example | |
| 485 @end group | |
| 486 @end example | |
| 487 | |
| 488 which produces | |
| 489 | |
| 490 @example | |
| 491 @group | |
| 492 @code{2 * 2} | |
| 493 @result{} 4 | |
| 494 @end group | |
| 495 @end example | |
| 496 | |
| 497 The @code{@@group} block prevents the example from being split across a | |
| 498 page boundary, while the @code{@@result@{@}} macro produces a right | |
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499 arrow signifying the result of a command. If your example is larger than |
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500 20 lines it is better NOT to use grouping so that a reasonable page boundary |
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501 can be calculated. |
| 6574 | 502 |
| 8828 | 503 In many cases a function has multiple ways in which it can be called, |
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504 and the @code{@@deftypefnx} macro can be used to give alternatives. For |
| 6574 | 505 example |
| 506 | |
| 507 @example | |
| 508 @group | |
| 509 -*- texinfo -*- | |
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510 @@deftypefn@{Function File@} @{@@var@{a@} =@} fn (@@var@{x@}, @dots{}) |
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511 @@deftypefnx@{Function File@} @{@@var@{a@} =@} fn (@@var@{y@}, @dots{}) |
| 6574 | 512 Help text in Texinfo format. |
| 513 @@end deftypefn | |
| 514 @end group | |
| 515 @end example | |
| 516 | |
| 517 Many complete examples of Texinfo documentation can be taken from the | |
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518 help strings for the Octave functions themselves. A relatively complete |
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519 example of which is the @code{nchoosek} function. The Texinfo |
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520 documentation string for @code{nchoosek} is |
| 6574 | 521 |
| 522 @example | |
| 523 -*- texinfo -*- | |
| 7081 | 524 @@deftypefn @{Function File@} @{@} nchoosek (@@var@{n@}, @@var@{k@}) |
| 6574 | 525 |
| 7081 | 526 Compute the binomial coefficient or all combinations of |
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527 @@var@{n@}. If @@var@{n@} is a scalar then, calculate the |
| 7081 | 528 binomial coefficient of @@var@{n@} and @@var@{k@}, defined as |
| 6574 | 529 |
| 530 @@tex | |
| 531 $$ | |
| 532 @{n \choose k@} = @{n (n-1) (n-2) \cdots (n-k+1) \over k!@} | |
| 533 $$ | |
| 534 @@end tex | |
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535 @@ifnottex |
| 6574 | 536 |
| 537 @@example | |
| 538 @@group | |
| 539 / \ | |
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540 | n | n (n-1) (n-2) @dots{} (n-k+1) |
| 6574 | 541 | | = ------------------------- |
| 542 | k | k! | |
| 543 \ / | |
| 544 @@end group | |
| 545 @@end example | |
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546 @@end ifnottex |
| 6574 | 547 |
| 7081 | 548 If @@var@{n@} is a vector, this generates all combinations |
| 549 of the elements of @@var@{n@}, taken @@var@{k@} at a time, | |
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550 one row per combination. The resulting @@var@{c@} has size |
| 7081 | 551 @@code@{[nchoosek (length (@@var@{n@}),@@var@{k@}), @@var@{k@}]@}. |
| 6574 | 552 |
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553 @@code@{nchoosek@} works only for non-negative integer arguments; use |
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554 @@code@{bincoeff@} for non-integer scalar arguments and for using vector |
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555 arguments to compute many coefficients at once. |
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556 |
| 6574 | 557 @@seealso@{bincoeff@} |
| 558 @@end deftypefn | |
| 559 @end example | |
| 560 | |
| 561 which demonstrates most of the concepts discussed above. | |
| 562 @iftex | |
| 563 This documentation string renders as | |
| 564 | |
| 565 @c Note actually use the output of info below rather than try and | |
| 566 @c reproduce it here to prevent it looking different than how it would | |
| 567 @c appear with info. | |
| 568 @example | |
| 569 @group | |
| 570 -- Function File: C = nchoosek (N, K) | |
| 7081 | 571 Compute the binomial coefficient or all combinations |
| 572 of N. If N is a scalar then, calculate the binomial | |
| 573 coefficient of N and K, defined as | |
| 6574 | 574 |
| 575 / \ | |
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576 | n | n (n-1) (n-2) @dots{} (n-k+1) n! |
| 7081 | 577 | | = ------------------------- = --------- |
| 578 | k | k! k! (n-k)! | |
| 6574 | 579 \ / |
| 580 | |
| 7081 | 581 If N is a vector generate all combinations of the |
| 582 elements of N, taken K at a time, one row per | |
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583 combination. The resulting C has size `[nchoosek |
| 7081 | 584 (length (N), K), K]'. |
| 6574 | 585 |
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586 `nchoosek' works only for non-negative integer |
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587 arguments; use `bincoeff' for non-integer scalar |
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588 arguments and for using vector arguments to compute |
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589 many coefficients at once. |
| 6574 | 590 |
| 591 See also: bincoeff. | |
| 592 @end group | |
| 593 @end example | |
| 594 | |
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595 using info, whereas in a printed documentation using @TeX{} it will appear |
| 6574 | 596 as |
| 597 | |
| 598 @deftypefn {Function File} {@var{c} =} nchoosek (@var{n}, @var{k}) | |
| 599 | |
| 6576 | 600 Compute the binomial coefficient or all combinations of @var{n}. |
| 6574 | 601 If @var{n} is a scalar then, calculate the binomial coefficient |
| 602 of @var{n} and @var{k}, defined as | |
| 603 | |
| 604 @tex | |
| 605 $$ | |
| 606 {n \choose k} = {n (n-1) (n-2) \cdots (n-k+1) \over k!} | |
| 607 $$ | |
| 608 @end tex | |
| 609 | |
| 610 If @var{n} is a vector generate all combinations of the elements | |
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611 of @var{n}, taken @var{k} at a time, one row per combination. The |
| 6574 | 612 resulting @var{c} has size @code{[nchoosek (length (@var{n}), |
| 613 @var{k}), @var{k}]}. | |
| 614 | |
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615 @code{nchoosek} works only for non-negative integer arguments; use |
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616 @code{bincoeff} for non-integer scalar arguments and for using vector |
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617 arguments to compute many coefficients at once. |
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618 |
| 6574 | 619 @seealso{bincoeff} |
| 620 @end deftypefn | |
| 621 | |
| 622 @end iftex |