Mercurial > hg > octave-lyh
annotate doc/faq/OctaveFAQ.texi @ 11463:ae96756561d0
fixing bug #32074
| author | Konstantinos Poulios <logari81@googlemail.com> |
|---|---|
| date | Sat, 08 Jan 2011 00:13:29 +0100 |
| parents | 0d4613a736e9 |
| children | fd0a3ac60b0e |
| rev | line source |
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| 9245 | 1 % Copyright (C) 1997, 1998, 1999, 2001, 2003, 2004, 2005, 2007, 2008, 2009 |
| 8920 | 2 % John W. Eaton |
| 7018 | 3 % |
| 4 % This file is part of Octave. | |
| 5 % | |
| 6 % Octave is free software; you can redistribute it and/or modify it | |
| 7 % under the terms of the GNU General Public License as published by the | |
| 8 % Free Software Foundation; either version 3 of the License, or (at | |
| 9 % your option) any later version. | |
| 10 % | |
| 11 % Octave is distributed in the hope that it will be useful, but WITHOUT | |
| 12 % ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 % FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 % for more details. | |
| 15 % | |
| 16 % You should have received a copy of the GNU General Public License | |
| 17 % along with Octave; see the file COPYING. If not, see | |
| 18 % <http://www.gnu.org/licenses/>. | |
| 19 | |
| 2866 | 20 \input texinfo.tex @c -*-texinfo-*- |
| 21 | |
|
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22 @setfilename OctaveFAQ.info |
| 2866 | 23 @settitle Frequently asked questions about Octave (with answers) |
| 24 | |
| 25 @setchapternewpage off | |
| 5099 | 26 @direntry |
|
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27 * OctaveFAQ: (OctaveFAQ). Frequently asked questions about Octave |
| 5099 | 28 @end direntry |
| 2866 | 29 @titlepage |
| 30 @title Octave FAQ | |
| 31 @subtitle Frequently asked questions about Octave | |
| 8128 | 32 @subtitle September 2008 |
| 2866 | 33 @sp 1 |
| 6900 | 34 @author John W. Eaton and David Bateman |
| 2866 | 35 @page |
| 36 @end titlepage | |
| 37 | |
| 5423 | 38 @ifnottex |
| 4830 | 39 @node Top |
| 2866 | 40 @top |
| 41 @unnumbered Preface | |
| 42 @cindex FAQ for Octave, latest version | |
| 5423 | 43 @end ifnottex |
| 2866 | 44 |
| 45 This is a list of frequently asked questions (FAQ) for Octave users. | |
| 46 | |
| 6584 | 47 We are always looking for new questions (@emph{with} answers), better |
| 48 answers, or both. Please send suggestions to @email{bug@@octave.org}. | |
| 49 If you have general questions about Octave, or need help for something | |
| 50 that is not covered by the Octave manual or the FAQ, please use the | |
| 51 @email{help@@octave.org} mailing list. | |
| 2866 | 52 |
| 53 This FAQ is intended to supplement, not replace, the Octave manual. | |
| 6584 | 54 Before posting a question to the @email{help@@octave.org} mailing list, |
| 55 you should first check to see if the topic is covered in the manual. | |
| 2866 | 56 |
| 57 @menu | |
| 6583 | 58 * What is Octave?:: |
| 9076 | 59 * Licensing Issues:: |
| 6583 | 60 * How can I cite Octave?:: |
| 8128 | 61 * Series 3.0.N:: |
| 6583 | 62 * Octave Features:: |
| 63 * Learning more about Octave:: | |
| 64 * Getting Octave:: | |
| 65 * Installation:: | |
| 2866 | 66 * Common problems:: |
| 6584 | 67 * How do I ...?:: |
| 6583 | 68 * MATLAB compatibility:: |
| 2866 | 69 * Index:: |
| 70 @end menu | |
| 71 | |
| 4830 | 72 @node What is Octave? |
| 2866 | 73 @chapter What is Octave? |
| 74 | |
| 75 Octave is a high-level interactive language, primarily intended for | |
| 76 numerical computations that is mostly compatible with | |
| 77 @sc{Matlab}.@footnote{@sc{Matlab} is a registered trademark of The MathWorks, | |
| 6583 | 78 Inc.} |
| 2866 | 79 |
| 6583 | 80 Octave can do arithmetic for real, complex or integer-valued scalars |
| 81 and matrices, solve sets of nonlinear algebraic equations, integrate | |
| 82 functions over finite and infinite intervals, and integrate systems of | |
| 83 ordinary differential and differential-algebraic equations. | |
| 2866 | 84 |
| 85 Octave uses the GNU readline library to handle reading and editing | |
| 86 input. By default, the line editing commands are similar to the | |
| 87 cursor movement commands used by GNU Emacs, and a vi-style line | |
| 88 editing interface is also available. At the end of each session, the | |
| 89 command history is saved, so that commands entered during previous | |
| 90 sessions are not lost. | |
| 91 | |
| 6879 | 92 The Octave distribution includes a 590+ page Texinfo manual. Access |
| 2866 | 93 to the complete text of the manual is available via the help command |
| 6583 | 94 @c really, the *complete* text? |
| 2866 | 95 at the Octave prompt. |
| 96 | |
| 6583 | 97 @menu |
| 98 * Who develops Octave?:: | |
| 6584 | 99 * Why GNU Octave?:: |
| 6583 | 100 * What version should I use?:: |
| 101 * On what platforms does Octave run?:: | |
| 102 @end menu | |
| 103 | |
| 104 @node Who develops Octave? | |
| 105 @section Who develops Octave? | |
| 106 | |
| 6584 | 107 Discussions about writing the software that would eventually become |
| 108 Octave started in about 1988 with James B. Rawlings and John W. Eaton at | |
| 109 the University of Texas. John W. Eaton was the original author of | |
| 110 Octave, starting full-time development in February 1992. He is still | |
| 111 the primary maintainer. The community | |
| 112 of users/developers has in addition contributed some code and fuels the | |
| 113 discussion on the mailing lists @email{help@@octave.org} (user forum), | |
| 114 @email{bug@@octave.org} (bug reports), @email{maintainers@@octave.org} | |
| 115 (development issues), and @email{octave-dev@@lists.sourceforge.net} (all | |
| 116 things related to the Octave Forge repository of user-contributed | |
| 117 functions). | |
| 6583 | 118 |
| 6584 | 119 @node Why GNU Octave? |
| 120 @section Why GNU Octave? | |
| 6583 | 121 |
| 6584 | 122 The GNU Project was launched in 1984 to develop a complete Unix-like |
| 123 operating system which is free software: the GNU system. | |
| 124 | |
| 125 GNU is a recursive acronym for ``GNU's Not Unix''; it is pronounced | |
| 126 guh-noo, approximately like canoe. | |
| 6583 | 127 |
| 6584 | 128 The Free Software Foundation (FSF) is the principal organizational |
| 129 sponsor of the GNU Project. | |
| 130 | |
| 131 Octave became GNU Octave in 1997 (beginning with version 2.0.6). This | |
| 132 meant agreeing to consider Octave a part of the GNU Project and support | |
| 133 the efforts of the FSF. However, Octave is not and has never been | |
| 134 developed by the FSF. | |
| 135 | |
| 136 For more information about the GNU project, see @url{www.gnu.org}. | |
| 6583 | 137 |
| 138 @cindex FSF [Free Software Foundation] | |
| 139 @cindex GNU [GNU's not unix] | |
| 140 | |
| 141 @node What version should I use? | |
| 142 @section What version should I use? | |
| 143 | |
| 144 In general, you will find the latest version on | |
| 6584 | 145 @url{http://www.octave.org/download.html}. It is |
| 6583 | 146 recommended to use the ``testing'' version of octave for general use, |
| 147 and the ``development'' version if you want the latest features. | |
| 148 | |
| 149 A list of user-visible changes since the last release is available in | |
| 150 the file @file{NEWS}. The file @file{ChangeLog} in the source | |
| 151 distribution contains a more detailed record of changes made since the | |
| 152 last release. | |
| 153 | |
| 154 @node On what platforms does Octave run? | |
| 155 @section On what platforms does Octave run? | |
| 156 | |
| 6584 | 157 Octave runs on various Unices---at least Linux and Solaris, Mac OS X, |
| 158 Windows and anything you can compile it on. Binary distributions exist | |
| 6583 | 159 at least for Debian, Suse, Fedora and RedHat Linuxes (Intel and AMD |
| 160 CPUs, at least), for Mac Os X and Windows' 98, 2000 and XP. | |
| 161 | |
| 2866 | 162 Two and three dimensional plotting is fully supported using gnuplot. |
| 163 | |
| 164 The underlying numerical solvers are currently standard Fortran ones | |
| 165 like Lapack, Linpack, Odepack, the Blas, etc., packaged in a library | |
| 166 of C++ classes. If possible, the Fortran subroutines are compiled | |
| 167 with the system's Fortran compiler, and called directly from the C++ | |
| 168 functions. If that's not possible, you can still compile Octave if | |
| 169 you have the free Fortran to C translator f2c. | |
| 170 | |
| 171 Octave is also free software; you can redistribute it and/or modify it | |
| 172 under the terms of the GNU General Public License as published by the | |
| 173 Free Software Foundation. | |
| 174 | |
| 9076 | 175 @node Licensing Issues |
| 176 @chapter Licensing Issues | |
| 177 | |
| 178 @menu | |
| 179 * If I write code using Octave do I have to release it under the GPL?: GPL | |
| 180 * Since the MEX interface allows plugins to be distributed under terms that are incompatible with the GPL, does this mean that you are encouraging people to to write non-free software for Octave?: Licensing MEX Files | |
| 181 * I wrote a program that links with Octave libraries and I don't want to release it under the terms of the GPL. Will you change the license of the Octave libraries for me?: Requesting License Changes | |
| 182 @end menu | |
| 183 | |
| 184 @node GPL | |
| 185 @section If I write code using Octave do I have to release it under the GPL? | |
| 186 | |
| 187 The answer depends on precisely how the code is written and how it works. | |
| 188 | |
| 189 Code written entirely in the scripting language of Octave | |
| 190 (interpreted code in .m files) may be released under the terms of | |
| 191 whatever license you choose. | |
| 192 | |
| 193 Code written using Octave's native plug-in interface (also known | |
| 194 as a .oct file) necessarily links with Octave internals and is | |
| 195 considered a derivative work of Octave and therefore must be | |
| 196 released under terms that are compatible with the GPL. | |
| 197 | |
| 198 Code written using Octave's implementation of the Matlab MEX | |
| 199 interface may be released under the terms of whatever license you | |
| 200 choose, provided that the following conditions are met: | |
| 201 | |
| 202 @enumerate | |
| 203 @item | |
| 204 The plugin should not use any bindings that are specific to Octave. In | |
| 205 other words, the MEX file must use the MEX interface only, and not also | |
| 206 call on other Octave internals. It should be possible in principle to | |
| 207 use the MEX file with other programs that implement the MEX interface | |
| 208 (e.g., Matlab). | |
| 209 | |
| 210 @item | |
| 211 The MEX file should not be distributed together with Octave in such a | |
| 212 way that they effectively create a single work. For example, you should | |
| 213 not distribute the MEX file and Octave together in a single package such | |
| 214 that Octave automatically loads and runs the MEX file when it starts up. | |
| 215 There are other possible ways that you might effectively create a single | |
| 216 work; this is just one example. | |
| 217 @end enumerate | |
| 218 | |
| 219 A program that embeds the Octave interpreter (e.g., by calling the | |
| 220 "octave_main" function), or that calls functions from Octave's | |
| 221 libraries (e.g., liboctinterp, liboctave, or libcruft) is | |
| 222 considered a derivative work of Octave and therefore must be | |
| 223 released under terms that are compatible with the GPL. | |
| 224 | |
| 225 @node Licensing MEX Files | |
| 226 @section Since the MEX interface allows plugins to be distributed under terms that are incompatible with the GPL, does this mean that you are encouraging people to to write non-free software for Octave? | |
| 227 | |
| 228 No. The original reason for implementing the MEX interface for Octave | |
| 229 was to allow Octave to run free software that uses MEX files (the | |
| 230 particular goal was to run SundialsTB in Octave). The intent was to | |
| 231 liberate that software from Matlab and increase the amount of free | |
| 232 software available to Octave users, not to enable people to write | |
| 233 proprietary code for Octave. For the good of the community, we strongly | |
| 234 encourage users of Octave to release the code they write for Octave | |
| 235 under terms that are compatible with the GPL. | |
| 236 | |
| 237 @node Requesting License Changes | |
| 238 @section I wrote a program that links with Octave libraries and I don't want to release it under the terms of the GPL. Will you change the license of the Octave libraries for me? | |
| 239 | |
| 240 No. Instead of asking us to change the licensing terms for Octave, we | |
| 241 recommend that you release your program under terms that are compatible | |
| 242 with the GPL so that the free software community can benefit from your | |
| 243 work the same as you have benefitted from the work of all the people who | |
| 244 have contributed to Octave. | |
| 245 | |
| 4830 | 246 @node How can I cite Octave? |
| 247 @chapter How can I cite Octave? | |
| 4831 | 248 |
| 249 Pointing to @url{http://www.octave.org} is good, because that gives | |
| 250 people a direct way to find out more. If citation of a URL is not | |
| 251 allowed by a publisher, or if you also want to point to a traditional | |
| 252 reference, then you can cite the Octave manual: | |
| 4830 | 253 |
| 254 @example | |
| 255 @group | |
| 8334 | 256 @@BOOK@{eaton:2008, |
| 257 author = "John W. Eaton and David Bateman and Søren Hauberg", | |
| 258 title = "GNU Octave Manual Version 3", | |
| 6584 | 259 publisher = "Network Theory Limited", |
| 8334 | 260 year = "2008", |
| 261 isbn = "0-9546120-6-X" | |
| 6584 | 262 @} |
| 4830 | 263 @end group |
| 264 @end example | |
| 265 | |
| 8128 | 266 @node Series 3.0.N |
| 267 @chapter What's new in version series 3.0.N and 3.1.N of Octave | |
| 6583 | 268 |
| 8128 | 269 The 3.0.N series has enough new features to justify a major version |
| 270 number change. The 3.0.N series brings | |
| 6583 | 271 |
| 272 @itemize @bullet | |
| 273 | |
| 274 @item integer types | |
| 275 | |
| 276 @item fixed point arithmetic | |
| 277 | |
| 278 @item sparse matrices | |
| 279 | |
| 280 @item Linear programming code based on GLPK | |
| 281 | |
| 282 @item 64-bit compilation support | |
| 283 | |
| 284 @item gzipped files and stream and consequently support of matlab v7 files | |
| 2866 | 285 |
| 6583 | 286 @item better support for both msvc and mingw |
| 287 | |
| 7116 | 288 @item a fully compatible MEX interface |
| 6583 | 289 |
| 6606 | 290 @item many many other minor features and compatibility changes |
| 6583 | 291 |
| 292 @end itemize | |
| 293 | |
| 6735 | 294 Here are some features that have been around since 2.1.N |
| 6583 | 295 |
| 296 @itemize @bullet | |
| 2866 | 297 |
| 6583 | 298 @item NDarrays |
| 299 | |
| 300 @item cells | |
| 301 | |
| 302 @end itemize | |
| 303 | |
| 8128 | 304 The 3.1.N series is the current development release and will become a |
| 305 3.2.N release in the future. This series brings the new features | |
| 306 | |
| 307 @itemize | |
| 308 @item OpenGL backend | |
| 309 | |
| 310 An experimental OpenGL graphics backend to replace the gnuplot | |
| 311 | |
| 312 @item Object Orient Programming | |
| 313 | |
| 314 @item Block comments | |
| 315 | |
| 316 @item imwrite and imread | |
| 317 | |
| 318 The functions are based on the GraphicsMagick library. | |
| 319 | |
| 320 @item Lazy transpose | |
| 321 | |
| 322 Special treatment in the parser of things like "a' * b", where the | |
| 323 transpose is never explicitly formed but a flag is rather passed to the | |
| 324 underlying LAPACK code. | |
| 325 | |
| 326 @item Single precision type | |
| 8292 | 327 |
| 328 @item Improved array indexing | |
| 329 The underlying code used for indexing of arrays has been completely | |
| 330 rewritten and so the indexing of arrays is now significantly faster. | |
| 8128 | 331 @end itemize |
| 332 | |
| 333 | |
| 4830 | 334 @node Octave Features |
| 2866 | 335 @chapter What features are unique to Octave? |
| 336 | |
| 337 @menu | |
| 6583 | 338 * Functions defined on the command-line:: |
| 339 * Comments with #:: | |
| 340 * Strings delimitted by double quotes ":: | |
| 341 * Line continuation by backslash:: | |
| 342 * Informative block closing:: | |
| 343 * Coherent syntax:: | |
| 344 * Exclamation mark as not operator:: | |
| 2866 | 345 * Increment and decrement operators:: |
| 346 * Unwind-protect:: | |
| 6583 | 347 * Built-in ODE and DAE solvers:: |
| 2866 | 348 @end menu |
| 349 | |
| 8128 | 350 This section refers to Matlab R2008b and Octave 2.1.51. |
| 2866 | 351 |
| 6583 | 352 @node Functions defined on the command-line |
| 353 @section Functions defined on the command-line | |
| 2866 | 354 |
| 6583 | 355 Functions can be defined by entering code on the command line, a |
| 6584 | 356 feature not supported by the other leading brand. For example, you may |
| 6583 | 357 type: |
| 2866 | 358 |
| 359 @example | |
| 360 @group | |
| 6583 | 361 octave:1> function s = hello_string (to_who) |
| 362 > ## Say hello | |
| 363 > if nargin<1, to_who = "World"; end | |
| 364 > s = ["Hello ",\ | |
| 365 > to_who]; | |
| 366 > endfunction | |
| 367 octave:2> hello_string ("Moon") | |
| 368 ans = Hello Moon | |
| 2866 | 369 @end group |
| 370 @end example | |
| 371 | |
| 6583 | 372 @node Comments with # |
| 373 @section Comments with # | |
| 374 | |
| 6584 | 375 The pound character, @samp{#}, may be used to start comments, in addition |
| 376 to @samp{%}. See the previous example. The major advantage of this is | |
| 377 that as @samp{#} is also a comment character for unix script files, any | |
| 378 file that starts with a string like @samp{#! /usr/bin/octave -q} will be | |
| 379 treated as an octave script and be executed by octave. | |
| 2866 | 380 |
| 6583 | 381 @node Strings delimitted by double quotes " |
| 382 @section Strings delimitted by double quotes " | |
| 6584 | 383 The double quote, @samp{"}, may be used to delimit strings, in addition to |
| 384 the single quote @samp{'}. See the previous example. Also, double-quoted | |
| 385 strings include backslash interpretation (like C++, C, and Perl) while | |
| 386 single quoted are uninterpreted (like Matlab and Perl). | |
| 6583 | 387 |
| 388 @node Line continuation by backslash | |
| 389 @section Line continuation by backslash | |
| 390 | |
| 6584 | 391 Lines can be continued with a backslash, @samp{\}, in addition to three |
| 392 points @samp{@dots{}}. See the previous example. | |
| 6583 | 393 |
| 394 @node Informative block closing | |
| 395 @section Informative block closing | |
| 396 | |
| 6584 | 397 You may close @code{function}, @code{for}, @code{while}, @code{if}, |
| 398 @dots{} blocks with @code{endfunction}, @code{endfor}, @code{endwhile}, | |
| 399 @dots{} keywords in addition to using @code{end}. As with Matlab, the | |
| 400 @code{end} (or @code{endfunction}) keyword that marks the end of a | |
| 401 function defined in a @file{.m} file is optional. | |
| 2866 | 402 |
| 6583 | 403 @node Coherent syntax |
| 404 @section Coherent syntax | |
| 405 | |
| 406 Indexing other things than variables is possible, as in: | |
| 407 @example | |
| 408 @group | |
| 409 octave:1> [3 1 4 1 5 9](3) | |
| 410 ans = 4 | |
| 411 octave:2> cos([0 pi pi/4 7])(3) | |
| 412 ans = 0.70711 | |
| 413 @end group | |
| 414 @end example | |
| 415 | |
| 416 @node Exclamation mark as not operator | |
| 417 @section Exclamation mark as not operator | |
| 418 | |
| 419 The exclamation mark '!' (aka ``Bang!'') is a negation operator, just | |
| 420 like the tilde '~': | |
| 2866 | 421 |
| 422 @example | |
| 423 @group | |
| 6583 | 424 octave:1> if ! strcmp (program_name, "octave"), |
| 425 > "It's an error" | |
| 426 > else | |
| 427 > "It works!" | |
| 428 > end | |
| 429 ans = It works! | |
| 2866 | 430 @end group |
| 431 @end example | |
| 432 | |
| 4830 | 433 @node Increment and decrement operators |
| 2866 | 434 @section Increment and decrement operators |
| 435 | |
| 436 @cindex Increment operators | |
| 437 @cindex Decrement operators | |
| 438 @cindex Operators, increment | |
| 439 @cindex Operators, decrement | |
| 440 | |
| 6584 | 441 If you like the @samp{++}, @samp{+=} etc operators, rejoice! |
| 2866 | 442 Octave includes the C-like increment and decrement operators @samp{++} |
| 6583 | 443 and @samp{--} in both their prefix and postfix forms, in addition to |
| 444 @samp{+=}, @samp{-=}, @samp{*=}, @samp{/=}, @samp{^=}, @samp{.*=}, | |
| 445 @samp{./=}, and @samp{.^=}. | |
| 2866 | 446 |
| 447 For example, to pre-increment the variable @var{x}, you would write | |
| 448 @code{++@var{x}}. This would add one to @var{x} and then return the new | |
| 449 value of @var{x} as the result of the expression. It is exactly the | |
| 450 same as the expression @code{@var{x} = @var{x} + 1}. | |
| 451 | |
| 6584 | 452 To post-increment a variable @var{x}, you would write @code{x++}. |
| 2866 | 453 This adds one to the variable @var{x}, but returns the value that |
| 454 @var{x} had prior to incrementing it. For example, if @var{x} is equal | |
| 6584 | 455 to 2, the result of the expression @code{x++} is 2, and the new |
| 2866 | 456 value of @var{x} is 3. |
| 457 | |
| 458 For matrix and vector arguments, the increment and decrement operators | |
| 459 work on each element of the operand. | |
| 460 | |
| 461 | |
| 4830 | 462 @node Unwind-protect |
| 2866 | 463 @section Unwind-protect |
| 464 | |
| 465 @cindex Unwind-protect | |
| 466 | |
| 467 Octave supports a limited form of exception handling modelled after the | |
| 468 unwind-protect form of Lisp. The general form of an | |
| 469 @code{unwind_protect} block looks like this: | |
| 470 | |
| 471 @example | |
| 472 @group | |
| 473 unwind_protect | |
| 474 @var{body} | |
| 475 unwind_protect_cleanup | |
| 476 @var{cleanup} | |
| 477 end_unwind_protect | |
| 478 @end group | |
| 479 @end example | |
| 480 | |
| 481 @noindent | |
| 482 Where @var{body} and @var{cleanup} are both optional and may contain any | |
| 483 Octave expressions or commands. The statements in @var{cleanup} are | |
| 484 guaranteed to be executed regardless of how control exits @var{body}. | |
| 485 | |
| 486 The @code{unwind_protect} statement is often used to reliably restore | |
| 487 the values of global variables that need to be temporarily changed. | |
| 488 | |
| 8128 | 489 Matlab can be made to do something similar with their @code{OnCleanUp} |
| 490 function that was introduced in 2008a. | |
| 491 | |
| 4830 | 492 @node Built-in ODE and DAE solvers |
| 2866 | 493 @section Built-in ODE and DAE solvers |
| 494 | |
| 495 @cindex DASSL | |
| 496 @cindex LSODE | |
| 497 | |
| 498 Octave includes LSODE and DASSL for solving systems of stiff ordinary | |
| 499 differential and differential-algebraic equations. These functions are | |
| 500 built in to the interpreter. | |
| 501 | |
| 6583 | 502 @node Learning more about Octave |
| 503 @chapter What documentation exists for Octave? | |
| 504 | |
| 505 @menu | |
| 506 * Documentation:: | |
| 507 * Getting additional help:: | |
| 508 * User community:: | |
| 509 * Bug reports:: | |
| 510 @end menu | |
| 511 | |
| 512 | |
| 4830 | 513 @node Documentation |
| 6583 | 514 @section What documentation exists for Octave? |
| 2866 | 515 |
| 516 @cindex Octave, documentation | |
| 517 | |
| 6879 | 518 The Octave distribution includes a 590+ page manual that is also |
| 2866 | 519 distributed under the terms of the GNU GPL. |
| 6583 | 520 It is available on the web at |
| 521 @url{http://www.octave.org/docs.html} and you will also | |
| 522 find there instructions on how to order a paper version. | |
| 523 | |
| 524 The complete text of the Octave manual is also available using the GNU | |
| 525 Info system via the GNU Emacs, info, or xinfo programs, or by using | |
| 526 the @samp{help -i} command to start the GNU info browser directly from | |
| 527 the Octave prompt. | |
| 528 | |
| 529 If you have problems using this documentation, or find that some topic | |
| 530 is not adequately explained, indexed, or cross-referenced, please send | |
| 6584 | 531 a bug report to @email{bug@@octave.org}. |
| 6583 | 532 |
| 2866 | 533 |
| 6583 | 534 @node Getting additional help |
| 535 @section Getting additional help | |
| 536 | |
| 537 @cindex Additional help | |
| 538 @cindex Mailing lists, help-octave | |
| 539 | |
| 6584 | 540 If you can't find an answer to your question, the |
| 541 @email{help@@octave.org} mailing list is available for questions related | |
| 542 to using, installing, and porting Octave that are not adequately | |
| 543 answered by the Octave manual or by this document. | |
| 6583 | 544 |
| 545 @node User community | |
| 546 @section User community | |
| 547 | |
| 6584 | 548 To subscribe to the list, go to @url{www.octave.org/archive.html} and |
| 549 follow the link to the subscription page for the list. | |
| 2866 | 550 |
| 6653 | 551 @strong{Please do not} send requests to be added or removed from the |
| 6583 | 552 mailing list, or other administrative trivia to the list itself. |
| 553 | |
| 554 An archive of old postings to the help-octave mailing list is maintained | |
| 555 on @url{http://www.octave.org/archive.html}. | |
| 556 | |
| 6584 | 557 You will also find some user advice and code spread over the web. Good |
| 6583 | 558 starting points are the Octave Wiki @url{http://wiki.octave.org} and |
|
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559 Octave-Forge @url{http://octave.sourceforge.net} |
| 6583 | 560 |
| 561 @node Bug reports | |
| 562 @section I think I have found a bug in Octave. | |
| 563 | |
| 564 @cindex Bug in Octave, newly found | |
| 565 | |
| 566 ``I think I have found a bug in Octave, but I'm not sure. How do I know, | |
| 567 and who should I tell?'' | |
| 2866 | 568 |
| 6583 | 569 @cindex Manual, for Octave |
| 570 | |
| 571 First, see the section on bugs and bug reports in the Octave manual. | |
| 572 When you report a bug, make sure to describe the type of computer you | |
| 573 are using, the version of the operating system it is running, and the | |
| 574 version of Octave that you are using. Also provide enough code so that | |
| 575 the Octave maintainers can duplicate your bug. | |
| 576 | |
| 577 If you have Octave working at all, the easiest way to do this is to use | |
| 578 the Octave function @code{bug_report}. When you execute this function, | |
| 579 Octave will prompt you for a subject and then invoke the editor on a | |
| 580 file that already contains all the configuration information. When you | |
| 581 exit the editor, Octave will mail the bug report for you (in a unix-like | |
| 582 operating system). | |
| 583 | |
| 584 @cindex Octave bug report | |
| 585 @cindex Mailing lists, bug-octave | |
| 586 | |
| 587 If for some reason you cannot use Octave's @code{bug_report} function, | |
| 6584 | 588 mail your bug report to @email{bug@@octave.org}. Your message needs to |
| 6583 | 589 include enough information to allow the maintainers of Octave to fix the |
| 590 bug. Please read the section on bugs and bug reports in the Octave | |
| 591 manual for a list of things that should be included in every bug report. | |
| 592 | |
| 2866 | 593 |
| 4830 | 594 @node Getting Octave |
| 6583 | 595 @chapter Getting Octave |
| 2866 | 596 |
| 597 @menu | |
| 6583 | 598 * Source code:: |
| 599 * Pre-compiled binary packages:: | |
| 600 * Octave for other platforms:: | |
| 2866 | 601 @end menu |
| 602 | |
| 6583 | 603 @node Source code |
| 604 @section Source code | |
| 605 @cindex Source code | |
| 2866 | 606 |
| 6583 | 607 Source code is available on the Octave development site, where you are |
| 608 sure to get the latest version. | |
| 2866 | 609 |
| 6583 | 610 @itemize @bullet |
| 611 @item @url{http://www.octave.org/download.html} | |
| 612 @item @url{ftp://ftp.octave.org/pub/octave/} | |
| 613 @end itemize | |
| 2866 | 614 |
| 6583 | 615 Since Octave is distrubted under the terms of the GPL, you can get |
| 616 Octave from a friend who has a copy, by anonymous FTP, or by ordering | |
| 617 a tape or CD-ROM from the Free Software Foundation (FSF). | |
| 2866 | 618 |
| 6583 | 619 @node Pre-compiled binary packages |
| 620 @section Pre-compiled binary packages | |
| 621 @cindex Pre-compiled binary packages | |
| 622 @cindex Binaries | |
| 2866 | 623 |
| 6584 | 624 The Octave project does not distribute binary packages, but other |
| 625 projects do. For an up-to-date listing of packagers, see: | |
| 2866 | 626 |
| 6583 | 627 @itemize @bullet |
| 628 @item @url{http://www.octave.org/download.html} | |
| 629 @item @url{http://wiki.octave.org/wiki.pl?CategoryInstall} | |
| 630 @end itemize | |
| 2866 | 631 |
| 6583 | 632 As of today, Octave binaries are available at least on Debian, RedHat, |
| 633 Suse and Fedora Linuxes, Mac OS X, Windows' 98, 2000 and XP. | |
| 2866 | 634 |
| 4830 | 635 @node Octave for other platforms |
| 2866 | 636 @section How do I get a copy of Octave for (some other platform)? |
| 637 | |
| 638 @cindex VMS support | |
| 639 @cindex VAX | |
| 640 @cindex MS-DOS support | |
| 3154 | 641 @cindex Windows support |
| 2866 | 642 @cindex DJGPP |
| 643 @cindex EMX | |
| 644 @cindex OS/2 support | |
| 645 | |
| 6879 | 646 Octave currently runs on Unix-like systems, Mac OS X, and Windows. |
| 647 It should be possible to make Octave work on other systems as well. | |
| 648 If you are interested in porting Octave to other systems, please contact | |
| 6584 | 649 @email{bug@@octave.org}. |
| 2866 | 650 |
| 6583 | 651 @c @menu |
| 652 @c * Octave for Unix:: | |
| 653 @c * Octave for other platforms:: | |
| 654 @c * latest versions:: | |
| 655 @c @end menu | |
| 2866 | 656 |
| 6583 | 657 @c @cindex Octave, ordering |
| 658 @c @cindex Octave, getting a copy | |
| 2866 | 659 |
| 4830 | 660 @node Installation |
| 2866 | 661 @chapter Installation Issues and Problems |
| 662 | |
| 663 @cindex Octave, building | |
| 664 | |
| 8128 | 665 Octave 3.2 require approximately 800MB of disk storage to unpack |
| 6584 | 666 and compile from source (considerably less if you don't compile with |
| 667 debugging symbols). Once installed, Octave requires approximately 200MB | |
| 668 of disk space (again, considerably less if you don't compile with | |
| 669 debugging symbols). | |
| 2866 | 670 |
| 671 @menu | |
| 672 * What else do I need?:: | |
| 673 * Other C++ compilers?:: | |
| 674 @end menu | |
| 675 | |
| 4830 | 676 @node What else do I need? |
| 2866 | 677 @section What else do I need? |
| 678 | |
| 679 @cindex GNU gcc | |
| 680 @cindex GNU g++ | |
| 681 @cindex libg++ | |
| 682 @cindex GNU Make | |
| 683 @cindex Flex | |
| 684 @cindex GNU Bison | |
| 685 | |
| 3154 | 686 To compile Octave, you will need a recent version of GNU Make. You |
| 6584 | 687 will also need GCC 3.3 or later, although GCC 4.1 or later is |
| 688 recommended. | |
| 3154 | 689 |
| 6584 | 690 @strong{You must have GNU Make to compile octave}. Octave's Makefiles |
| 3154 | 691 use features of GNU Make that are not present in other versions of make. |
| 692 GNU Make is very portable and easy to install. | |
| 2866 | 693 |
| 4830 | 694 @node Other C++ compilers? |
| 2866 | 695 @section Can I compile Octave with another C++ compiler? |
| 696 | |
| 6584 | 697 Yes, but development is done primarily with GCC, so you may hit some |
| 698 incompatibilities. Octave is intended to be portable to any standard | |
| 699 conforming compiler. If you have difficulties that you think are bugs, | |
| 700 please report them to the @email{bug@@octave.org} mailing list, or ask | |
| 701 for help on the @email{help@@octave.org} mailing list. | |
| 2866 | 702 |
| 4830 | 703 @node Common problems |
| 2866 | 704 @chapter Common problems |
| 705 | |
| 706 This list is probably far too short. Feel free to suggest additional | |
| 707 questions (preferably with answers!) | |
| 708 | |
| 709 @itemize @bullet | |
| 710 @item | |
| 711 Octave takes a long time to find symbols. | |
| 712 | |
| 6606 | 713 Octave uses the @code{genpath} function to recursively add directories |
| 6900 | 714 to the list of directories searched for function files. Check the list |
| 6606 | 715 of directories with the @code{path} command. If the path list is very |
| 716 long check your use of the @code{genpath} function. | |
| 6735 | 717 |
| 718 @item | |
| 6900 | 719 When plotting Octave occasionally gives me errors like @samp{gnuplot> 9 0.735604 |
| 720 line 26317: invalid command}. | |
| 6735 | 721 |
| 722 There is a known bug in gnuplot 4.2 that can cause an off by one error | |
| 723 while piping data to gnuplot. The relevant gnuplot bug report can be | |
| 724 found at @url{http://sourceforge.net/tracker/index.php?func=detail&aid=1716556&group_id=2055&atid=102055} | |
| 725 | |
| 726 If you have obtained your copy of Octave from a distribution please file | |
| 727 a bug report requesting that the fix reported in the above bug report be | |
| 728 included. | |
|
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729 |
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730 @item |
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731 I cannot install a package. Octave complains about a missing @code{mkoctfile}. |
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732 |
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733 Most distributions split Octave into several packages. The script |
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734 @code{mkoctfile} is then part of a separate package: |
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735 @itemize @minus |
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736 @item |
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737 Debian/Ubuntu |
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738 |
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739 @code{aptitude install octave3.0-headers} |
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740 |
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741 @item |
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742 Fedora |
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743 |
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744 @code{yum install octave-devel} |
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745 |
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746 @end itemize |
| 2866 | 747 @end itemize |
| 748 | |
| 6584 | 749 @node How do I ...? |
| 750 @chapter How do I ...? | |
| 2866 | 751 |
| 6583 | 752 @menu |
| 753 * How do I set the number of displayed decimals?:: | |
| 754 @end menu | |
| 2866 | 755 |
| 6583 | 756 @cindex Tips and tricks |
| 6584 | 757 @cindex How do I @dots{} ? |
| 2866 | 758 |
| 6583 | 759 @node How do I set the number of displayed decimals? |
| 760 @section How do I set the number of displayed decimals? | |
| 2866 | 761 |
| 762 @example | |
| 763 @group | |
| 6583 | 764 octave:1> format long |
| 765 octave:2> pi | |
| 766 pi = 3.14159265358979 | |
| 767 octave:3> format short | |
| 768 octave:4> pi | |
| 769 pi = 3.1416 | |
| 2866 | 770 @end group |
| 771 @end example | |
| 772 | |
| 4830 | 773 @node MATLAB compatibility |
| 2866 | 774 @chapter Porting programs from @sc{Matlab} to Octave |
| 775 | |
| 776 @cindex @sc{Matlab} compatibility | |
| 777 @cindex Compatibility with @sc{Matlab} | |
| 778 | |
| 6612 | 779 People often ask |
| 780 | |
| 2866 | 781 ``I wrote some code for @sc{Matlab}, and I want to get it running under |
| 782 Octave. Is there anything I should watch out for?'' | |
| 783 | |
| 6612 | 784 or alternatively |
| 785 | |
| 786 ``I wrote some code in Octave, and want to share it with @sc{Matlab} | |
| 6900 | 787 users. Is there anything I should watch out for?'' |
| 6612 | 788 |
| 6900 | 789 which is not quite the same thing. There are still a number of |
| 6612 | 790 differences between Octave and @sc{Matlab}, however in general |
| 791 differences between the two are considered as bugs. Octave might | |
| 792 consider that the bug is in @sc{Matlab} and do nothing about it, but | |
| 793 generally functionality is almost identical. If you find a difference | |
| 794 between Octave behavior and @sc{Matlab}, then you should send a | |
| 795 description of this difference (with code illustrating the difference, | |
| 796 if possible) to @email{bug@@octave.org}. | |
| 797 | |
| 798 Furthermore, Octave adds a few syntactical extensions to Matlab that | |
| 799 might cause some issues when exchanging files between Matlab and Octave | |
| 800 users. As both Octave and @sc{Matlab} are under constant development the | |
| 801 information in this section is subject to change at anytime. | |
| 802 | |
| 803 You should also look at the page | |
| 804 @url{http://octave.sourceforge.net/packages.html} and | |
| 805 @url{http://octave.sourceforge.net/doc/} that has a function reference | |
| 806 that is up to date. You can use this function reference to see the | |
| 807 number of octave function that are available and their @sc{Matlab} | |
| 808 compatibility. | |
| 809 | |
| 8128 | 810 The major differences between Octave 3.2.N and @sc{Matlab} R2008a are: |
| 6612 | 811 |
| 812 @itemize @bullet | |
| 813 @item Nested Functions | |
| 814 | |
| 6900 | 815 Octave doesn't yet have nested functions. That is |
| 2866 | 816 |
| 6612 | 817 @example |
| 818 @group | |
| 819 function y = foo (x) | |
| 6900 | 820 y = bar(x) |
| 821 function y = bar (x) | |
| 822 y = @dots{}; | |
| 823 end | |
| 6612 | 824 end |
| 825 @end group | |
| 826 @end example | |
| 827 | |
| 828 There was discussion in Octave of having these even prior to @sc{Matlab}, | |
| 829 and the decision was made not to have these in Octave at the time for | |
| 6900 | 830 compatibility. The above written with sub-functions functions would be |
| 6612 | 831 |
| 832 @example | |
| 833 @group | |
| 834 function y = foo (x) | |
| 835 y = bar(x) | |
| 836 end | |
| 837 function y = bar (x) | |
| 838 y = @dots{}; | |
| 839 end | |
| 840 @end group | |
| 841 @end example | |
| 842 | |
| 843 Now that @sc{Matlab} has recently introduced nested functions, Octave will | |
| 6900 | 844 probably have them soon as well. Until then nested functions in Octave |
| 6612 | 845 are treated as sub-functions with the same scoping rules as |
| 846 sub-functions. | |
| 847 | |
| 848 The authors of Octave consider the nested function scoping rules of | |
| 849 Matlab to be more problems than they are worth as they introduce | |
| 850 diffiult to find bugs as inadvertantly modifying a variable in a | |
| 851 nested function that is also used in the parent is particularly easy. | |
| 852 | |
| 853 @item Differences in core syntax | |
| 854 There a few core @sc{Matlab} syntaxes that are not accepted by Octave, | |
| 855 these being | |
| 856 | |
| 857 @itemize @bullet | |
| 2866 | 858 @item |
| 6612 | 859 Some limitations on the use of function handles. The major difference is |
| 6879 | 860 related to nested function scoping rules (as above) and their use with |
| 6612 | 861 function handles. |
| 2866 | 862 |
| 863 @item | |
| 6612 | 864 Some limitations of variable argument lists on the LHS of an expression, |
| 865 though the most common types are accepted. | |
| 866 | |
| 2866 | 867 @item |
| 8128 | 868 @sc{Matlab} classdef object oriented programming is not yet supportted, |
| 869 though work is underway and when development more on to Octave 3.3 this | |
| 870 will be included in teh development tree. | |
| 6612 | 871 @end itemize |
| 872 | |
| 873 @item Differences in core functions | |
| 874 A large number of the @sc{Matlab} core functions (ie those that are in | |
| 875 the core and not a toolbox) are implemented, and certainly all of the | |
| 876 commonly used ones. There are a few functions that aren't implemented, | |
| 6879 | 877 for example @code{condest} or to do with specific missing Octave functionality |
| 6612 | 878 (gui, dll, java, activex, dde, web, and serial functions). Some of the |
| 879 core functions have limitations that aren't in the @sc{Matlab} | |
| 6900 | 880 version. For example the @code{sprandn} function can not force a |
| 6735 | 881 particular condition number for the matrix like @sc{Matlab} can. |
| 6612 | 882 |
| 883 @item Just-In-Time compiler | |
| 884 @sc{Matlab} includes a "Just-In-Time" compiler. This compiler allows the | |
| 885 acceleration of for-loops in @sc{Matlab} to almost native performance with | |
| 886 certain restrictions. The JIT must know the return type of all functions | |
| 887 called in the loops and so you can't include user functions in the loop | |
| 6900 | 888 of JIT optimized loops. Octave doesn't have a JIT and so to some might |
| 889 seem slower than @sc{Matlab}. For this reason you must vectorize your code as | |
| 890 much as possible. The MathWorks themselves have a good document | |
| 891 discussing vectorization at | |
| 6612 | 892 @url{http://www.mathworks.com/support/tech-notes/1100/1109.html}. |
| 893 | |
| 894 @item Compiler | |
| 895 On a related point, there is no Octave compiler, and so you can't | |
| 896 convert your Octave code into a binary for additional speed or | |
| 6900 | 897 distribution. There is an example of how to do this at |
| 6612 | 898 @url{http://www.stud.tu-ilmenau.de/~rueckn/}, but this is a very early |
| 899 example code and would need lots of work to complete it. | |
| 900 | |
| 901 @item Graphic Handles | |
| 902 Up to Octave 2.9.9 there was no support for graphic handles in Octave | |
| 8128 | 903 itself. In the 3.2.N versions of Octave the support for graphics |
| 904 handles is converging towards full compatibility. The @code{patch} | |
| 905 function is currently limited to 2-D patches, due to an underlying | |
| 906 limitation in gnuplot. | |
| 6612 | 907 |
| 908 @item GUI | |
| 6900 | 909 There are no @sc{Matlab} compatible GUI functions. There are a number of |
| 910 bindings from Octave to Tcl/Tk, Vtk and zenity included in the | |
| 911 Octave Forge project (@url{http://octave.sourceforge.net}) for example | |
| 6612 | 912 that can be used for a GUI, but these are not @sc{Matlab} |
| 7116 | 913 compatible. Work on a matlab compatible GUI is in an alpha stage in the |
| 6879 | 914 JHandles package (@url{http://octave.sourceforge.net/jhandles/index.html}). |
| 915 This might be an issue if you intend to exchange Octave code with | |
| 916 @sc{Matlab} users. | |
| 6612 | 917 |
| 918 @item Simulink | |
| 919 Octave itself includes no Simulink support. Typically the simulink | |
| 920 models lag research and are less flexible, so shouldn't really be used | |
| 6900 | 921 in a research environment. However, some @sc{Matlab} users that try to |
| 922 use Octave complain about this lack. There is a similar package to | |
| 923 simulink for the Octave and R projects available at | |
| 924 @url{http://www.scicraft.org/} | |
| 6612 | 925 |
| 926 @item Mex-Files | |
| 927 Octave includes an API to the matlab MEX interface. However, as MEX is | |
| 6900 | 928 an API to the internals of @sc{Matlab} and the internals of Octave |
| 929 differ from @sc{Matlab}, there is necessarily a manipulation of the data | |
| 930 to convert from a MEX interface to the Octave equivalent. This is | |
| 931 notable for all complex matrices, where @sc{Matlab} stores complex | |
| 932 arrays as real and imaginary parts, whereas Octave respects the C99/C++ | |
| 933 standards of co-locating the real/imag parts in memory. Also due to the | |
| 934 way @sc{Matlab} allows access to the arrays passed through a pointer, | |
| 935 the MEX interface might require copies of arrays (even non complex | |
| 8128 | 936 ones). |
| 6612 | 937 |
| 938 @item Block comments | |
| 8128 | 939 Block comments denoted by "%@{" and "%@}" markers are supported by |
| 940 Octave with some limitations. The major limitation is that block | |
| 8292 | 941 comments are not supported within [] or @{@}. |
| 6612 | 942 |
| 943 @item Mat-File format | |
| 944 There are some differences in the mat v5 file format accepted by | |
| 945 Octave. @sc{Matlab} recently introduced the "-V7.3" save option which is | |
| 6900 | 946 an HDF5 format which is particularly useful for 64-bit platforms where |
| 6612 | 947 the standard matlab format can not correctly save variables.. Octave |
| 6900 | 948 accepts HDF5 files, but is not yet compatible with the "-v7.3" versions |
| 6612 | 949 produced by @sc{Matlab}. |
| 950 | |
| 8128 | 951 Although Octave can load inline abd function handles saved by |
| 952 @sc{Matlab}, it can not yet save them. | |
| 6612 | 953 |
| 954 Finally, Some multi-byte unicode characters aren't yet treated in | |
| 955 mat-files. | |
| 956 | |
| 957 @item Profiler | |
| 958 Octave doesn't have a profiler. Though there is a patch for a flat | |
| 959 profiler, that might become a real profiler sometime in the future. see | |
| 960 the thread | |
| 961 | |
| 962 @url{http://www.cae.wisc.edu/pipermail/octave-maintainers/2007-January/001685.html} | |
| 963 | |
| 964 for more details | |
| 965 | |
| 966 @item Toolboxes | |
| 967 Octave is a community project and so the toolboxes that exist are | |
| 6900 | 968 donated by those interested in them through the Octave Forge website |
| 6612 | 969 (@url{http://octave.sourceforge.net}). These might be lacking in certain |
| 970 functionality relative to the @sc{Matlab} toolboxes, and might not | |
| 971 exactly duplicate the matlab functionality or interface. | |
| 972 | |
| 973 @item Short-circuit & and | operators | |
| 6900 | 974 The @code{&} and @code{|} operators in @sc{Matlab} short-circuit when |
| 975 included in an if statemant and not otherwise. In Octave only the | |
| 976 @code{&&} and @code{||} short circuit. Note that this means that | |
| 6612 | 977 |
| 978 @example | |
| 979 @group | |
| 980 if (a | b) | |
| 981 @dots{} | |
| 982 end | |
| 983 @end group | |
| 984 @end example | |
| 985 | |
| 986 and | |
| 987 | |
| 988 @example | |
| 989 @group | |
| 990 t = a | b; | |
| 991 if t | |
| 992 @dots{} | |
| 993 end | |
| 994 @end group | |
| 995 @end example | |
| 996 | |
| 6900 | 997 @noindent |
| 6612 | 998 are different in @sc{Matlab}. This is really a @sc{Matlab} bug, but |
| 999 there is too much code out there that relies on this behavior to change | |
| 1000 it. Prefer the || and && operators in if statements if possible. | |
| 2866 | 1001 |
| 6612 | 1002 Note that the difference is also significant when either argument is a |
| 1003 function with side effects or if the first argument is a scalar and the | |
| 1004 second argument is an empty matrix. For example, note the difference | |
| 1005 between | |
| 1006 | |
| 1007 @example | |
| 1008 @group | |
| 1009 t = 1 | []; ## results in [], so... | |
| 1010 if (t) 1, end ## in if ([]), this is false. | |
| 1011 @end group | |
| 1012 @end example | |
| 1013 | |
| 1014 and | |
| 1015 | |
| 1016 @example | |
| 1017 if (1 | []) 1, end ## short circuits so condition is true. | |
| 1018 @end example | |
| 1019 | |
| 1020 Another case that is documented in the @sc{Matlab} manuals is that | |
| 1021 | |
| 1022 @example | |
| 1023 @group | |
| 1024 t = [1, 1] | [1, 2, 3]; ## error | |
| 1025 if ([1, 1] | [1, 2, 3]) 1, end ## OK | |
| 1026 @end group | |
| 1027 @end example | |
| 1028 | |
| 1029 Also @sc{Matlab} requires the operands of && and || to be scalar values but | |
| 1030 Octave does not (it just applies the rule that for an operand to be | |
| 1031 considered true, every element of the object must be nonzero or | |
| 1032 logically true). | |
| 1033 | |
| 1034 Finally, note the inconsistence of thinking of the condition of an if | |
| 1035 statement as being equivalent to @code{all(X(:))} when @var{X} is a | |
| 1036 matrix. This is true for all cases EXCEPT empty matrices: | |
| 1037 | |
| 1038 @example | |
| 1039 @group | |
| 1040 if ([0, 1]) == if (all ([0, 1])) ==> i.e., condition is false. | |
| 1041 if ([1, 1]) == if (all ([1, 1])) ==> i.e., condition is true. | |
| 1042 @end group | |
| 1043 @end example | |
| 1044 | |
| 1045 However, | |
| 1046 | |
| 1047 @example | |
| 1048 if ([]) != if (all ([])) | |
| 1049 @end example | |
| 1050 | |
| 6900 | 1051 because @code{samp ([]) == 1} (because, despite the name, it is really |
| 6612 | 1052 returning true if none of the elements of the matrix are zero, and since |
| 1053 there are no elements, well, none of them are zero). But, somewhere | |
| 1054 along the line, someone decided that if @code{([])} should be false. | |
| 1055 Mathworks probably thought it just looks wrong to have @code{[]} be true | |
| 1056 in this context even if you can use logical gymnastics to convince | |
| 1057 yourself that "all" the elements of a matrix that doesn't actually have | |
| 1058 any elements are nonzero. Octave however duplicates this behavior for if | |
| 1059 statements containing empty matrices. | |
| 1060 | |
| 8292 | 1061 @item Solvers for singular, under- and over-determined matrices |
| 1062 | |
| 1063 Matlab's solvers as used by the operators mldivide (\) and mrdivide (/), | |
| 1064 use a different approach than Octave's in the case of singular, under-, | |
| 1065 or over-determined matrices. In the case of a singular matrix, Matlab | |
| 1066 returns the result given by the LU decomposition, even though the underlying | |
| 1067 solver has flagged the result as erroneous. Octave has made the choice | |
| 1068 of falling back to a minimum norm solution of matrices that have been | |
| 1069 flagged as singular which arguably is a better result for these cases. | |
| 1070 | |
| 1071 In the case of under- or over-determined matrices, Octave continues to | |
| 1072 use a minimum norm solution, whereas Matlab uses an approach that is | |
| 1073 equivalent to | |
| 1074 | |
| 1075 @example | |
| 1076 @group | |
| 1077 function x = mldivide (A, b) | |
| 1078 [Q, R, E] = qr(A); | |
| 1079 x = [A \ b, E(:, 1:m) * (R(:, 1:m) \ (Q' * b))] | |
| 1080 end | |
| 1081 @end group | |
| 1082 @end example | |
| 1083 | |
| 1084 @noindent | |
| 1085 While this approach is certainly faster and uses less memory than | |
| 1086 Octave's minimum norm approach, this approach seems to be inferior in | |
| 1087 other ways. | |
| 1088 | |
| 1089 A numerical question arises: how big can the null space component become, | |
| 1090 relative to the minimum-norm solution? Can it be nicely bounded, or can it be | |
| 1091 arbitrarily big? Consider this example: | |
| 1092 | |
| 1093 @example | |
| 1094 @group | |
| 1095 m = 10; | |
| 1096 n = 10000; | |
| 1097 A = ones(m, n) + 1e-6 * randn(m,n); | |
| 1098 b = ones(m, 1) + 1e-6 * randn(m,1); | |
| 1099 norm(A \ b) | |
| 1100 @end group | |
| 1101 @end example | |
| 1102 | |
| 1103 @noindent | |
| 1104 while Octave's minimum-norm values are around 3e-2, Matlab's results | |
| 1105 are 50-times larger. For another issue, try this code: | |
| 1106 | |
| 1107 @example | |
| 1108 @group | |
| 1109 m = 5; | |
| 1110 n = 100; | |
| 1111 j = floor(m * rand(1, n)) + 1; | |
| 1112 b = ones(m, 1); | |
| 1113 A = zeros(m, n); | |
| 1114 A(sub2ind(size(A),j,1:n)) = 1; | |
| 1115 x = A \ b; | |
| 1116 [dummy,p] = sort(rand(1,n)); | |
| 1117 y = A(:,p)\b; | |
| 1118 norm(x(p)-y) | |
| 1119 @end group | |
| 1120 @end example | |
| 1121 | |
| 1122 @noindent | |
| 1123 It shows that unlike in Octave, mldivide in Matlab is not invariant | |
| 1124 with respect to column permutations. If there are multiple columns of | |
| 1125 the same norm, permuting columns of the matrix gets you different | |
| 1126 result than permuting the solution vector. This will surprise many | |
| 1127 users. | |
| 1128 | |
| 1129 Since the mldivide (\) and mrdivide (/) operators are often part of a more | |
| 1130 complex expression, where there is no room to react to warnings or flags, it | |
| 1131 should prefer intelligence (robustness) to speed, and so the Octave developers | |
| 1132 are firmly of the opinion that Octave's approach for singular, under- and | |
| 1133 over-determined matrices is a better choice that Matlab's | |
| 1134 | |
| 6612 | 1135 @item Octave extensions |
| 1136 The extensions in Octave over @sc{Matlab} syntax are | |
| 1137 very useful, but might cause issues when sharing with @sc{Matlab} users. | |
| 1138 A list of the major extensions that should be avoided to be compatible | |
| 1139 with @sc{Matlab} are | |
| 1140 | |
| 1141 @itemize @bullet | |
| 1142 @item | |
| 6900 | 1143 Comments in octave can be marked with @samp{#}. This allows POSIX |
| 1144 systems to have the first line as @samp{#! octave -q} and mark the script | |
| 6653 | 1145 itself executable. @sc{Matlab} doesn't have this feature due to the |
| 6900 | 1146 absence of comments starting with @samp{#}". |
| 2866 | 1147 |
| 6612 | 1148 @item |
| 1149 Code blocks like if, for, while, etc can be terminated with block | |
| 1150 specific terminations like "endif". @sc{Matlab} doesn't have this and | |
| 1151 all blocks must be terminated with "end" | |
| 1152 | |
| 1153 @item | |
| 1154 Octave has a lisp like unwind_protect block that allows blocks of | |
| 1155 code that terminate in an error to ensure that the variables that | |
| 1156 are touched are restored. You can do something similar with | |
| 6900 | 1157 @code{try}/@code{catch} combined with @samp{rethrow (lasterror ())} in |
| 1158 @sc{Matlab}, however rethrow and lasterror are only available in Octave 2.9.10 and later. | |
| 6612 | 1159 |
| 6900 | 1160 Note that using @code{try}/@code{catch} combined with @samp{rethrow |
|
8325
b93ac0586e4b
spelling corrections
Brian Gough<bjg@network-theory.co.uk>
parents:
8292
diff
changeset
|
1161 (lasterror ())} can not guarantee that global variables will be |
| 6900 | 1162 correctly reset, as it won't catch user interrupts with Ctrl-C. For |
| 1163 example | |
| 6612 | 1164 |
| 1165 @example | |
| 1166 @group | |
| 1167 global a | |
| 1168 a = 1; | |
| 1169 try | |
| 1170 _a = a; | |
| 1171 a = 2 | |
| 1172 while true | |
| 1173 end | |
| 1174 catch | |
| 1175 fprintf ('caught interrupt\n'); | |
| 1176 a = _a; | |
| 1177 rethrow (lasterror()); | |
| 1178 end | |
| 1179 @end group | |
| 1180 @end example | |
| 1181 | |
| 1182 @noindent | |
| 1183 compared to | |
| 1184 | |
| 1185 @example | |
| 1186 @group | |
| 1187 global a | |
| 1188 a = 1; | |
| 1189 unwind_protect | |
| 1190 _a = a; | |
| 1191 a = 2 | |
| 1192 while true | |
| 1193 end | |
| 1194 unwind_protect_cleanup | |
| 1195 fprintf ('caught interrupt\n'); | |
| 1196 a = _a; | |
| 1197 end | |
| 1198 @end group | |
| 1199 @end example | |
| 1200 | |
| 1201 Typing Ctrl-C in the first case returns the user directly to the | |
| 6879 | 1202 prompt, and the variable "a" is not reset to the saved value. In the |
| 6900 | 1203 second case the variable "a" is reset correctly. Therefore @sc{Matlab} |
| 6612 | 1204 gives no save way of temporarily changing global variables. |
| 1205 | |
| 1206 @item | |
| 1207 Indexing can be applied to all objects in Octave and not just | |
| 1208 variable. Therefore @code{sin(x)(1:10);} for example is perfectly valid | |
| 1209 in Octave but not @sc{Matlab}. To do the same in @sc{Matlab} you must do | |
| 1210 @code{y = sin(x); y = y([1:10]);} | |
| 1211 | |
| 1212 @item | |
| 6900 | 1213 Octave has the operators "++", "--", "-=", "+=", "*=", etc. As |
| 6612 | 1214 @sc{Matlab} doesn't, if you are sharing code these should be avoided. |
| 1215 | |
| 1216 @item | |
| 6900 | 1217 Character strings in Octave can be denoted with double or single |
| 1218 quotes. There is a subtle difference between the two in that escaped | |
| 1219 characters like @code{\n} (newline), @code{\t} (tab), etc are | |
| 1220 interpreted in double quoted strings but not single quoted strings. This | |
| 1221 difference is important on Windows platforms where the "\" character is | |
| 1222 used in path names, and so single quoted strings should be used in | |
| 1223 paths. @sc{Matlab} doesn't have double quoted strings and so they should | |
| 1224 be avoided if the code will be transfered to a @sc{Matlab} user. | |
| 6612 | 1225 @end itemize |
| 1226 | |
| 1227 @end itemize | |
| 2866 | 1228 |
| 4830 | 1229 @node Index |
| 2866 | 1230 @appendix Concept Index |
| 1231 | |
| 1232 @printindex cp | |
| 1233 | |
| 1234 @page | |
| 1235 @contents | |
| 1236 @bye |