Mercurial > hg > octave-lyh
annotate doc/interpreter/intro.txi @ 11463:ae96756561d0
fixing bug #32074
| author | Konstantinos Poulios <logari81@googlemail.com> |
|---|---|
| date | Sat, 08 Jan 2011 00:13:29 +0100 |
| parents | 322f43e0e170 |
| children | fd0a3ac60b0e |
| rev | line source |
|---|---|
| 8920 | 1 @c Copyright (C) 1996, 1997, 2007, 2008, 2009 John W. Eaton |
| 7018 | 2 @c |
| 3 @c This file is part of Octave. | |
| 4 @c | |
| 5 @c Octave is free software; you can redistribute it and/or modify it | |
| 6 @c under the terms of the GNU General Public License as published by the | |
| 7 @c Free Software Foundation; either version 3 of the License, or (at | |
| 8 @c your option) any later version. | |
| 9 @c | |
| 10 @c Octave is distributed in the hope that it will be useful, but WITHOUT | |
| 11 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 @c for more details. | |
| 14 @c | |
| 15 @c You should have received a copy of the GNU General Public License | |
| 16 @c along with Octave; see the file COPYING. If not, see | |
| 17 @c <http://www.gnu.org/licenses/>. | |
| 3294 | 18 |
| 4167 | 19 @node Introduction |
| 3294 | 20 @chapter A Brief Introduction to Octave |
| 21 @cindex introduction | |
| 22 | |
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23 GNU Octave is a high-level language, primarily intended for numerical |
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24 computations. It provides a convenient interactive command line |
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25 interface for solving linear and nonlinear problems numerically, and |
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26 for performing other numerical experiments. It may also be used as a |
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27 batch-oriented language for data processing. |
| 3294 | 28 |
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29 GNU Octave is freely redistributable software. You may redistribute |
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30 it and/or modify it under the terms of the GNU General Public License |
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31 as published by the Free Software Foundation. The GPL is included in |
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32 this manual in @ref{Copying}. |
| 3294 | 33 |
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34 This manual provides comprehensive documentation on how to install, |
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35 run, use, and extend GNU Octave. Additional chapters describe how |
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36 to report bugs and help contribute code. |
| 3294 | 37 |
| 38 This document corresponds to Octave version @value{VERSION}. | |
| 39 | |
| 40 @menu | |
| 41 * Running Octave:: | |
| 42 * Simple Examples:: | |
| 43 * Conventions:: | |
| 44 @end menu | |
| 45 | |
| 4167 | 46 @node Running Octave |
| 3294 | 47 @section Running Octave |
| 48 | |
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49 On most systems, Octave is started with the shell command |
| 3294 | 50 @samp{octave}. Octave displays an initial message and then a prompt |
| 51 indicating it is ready to accept input. You can begin typing Octave | |
| 52 commands immediately afterward. | |
| 53 | |
| 54 If you get into trouble, you can usually interrupt Octave by typing | |
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55 @kbd{Control-C} (written @kbd{C-c} for short). @kbd{C-c} gets |
| 3294 | 56 its name from the fact that you type it by holding down @key{CTRL} and |
| 57 then pressing @key{c}. Doing this will normally return you to Octave's | |
| 58 prompt. | |
| 59 | |
| 60 @cindex exiting octave | |
| 61 @cindex quitting octave | |
| 62 To exit Octave, type @kbd{quit}, or @kbd{exit} at the Octave prompt. | |
| 63 | |
| 64 On systems that support job control, you can suspend Octave by sending | |
| 65 it a @code{SIGTSTP} signal, usually by typing @kbd{C-z}. | |
| 66 | |
| 4167 | 67 @node Simple Examples |
| 3294 | 68 @section Simple Examples |
| 69 | |
| 70 The following chapters describe all of Octave's features in detail, but | |
| 71 before doing that, it might be helpful to give a sampling of some of its | |
| 72 capabilities. | |
| 73 | |
| 74 If you are new to Octave, I recommend that you try these examples to | |
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75 begin learning Octave by using it. Lines marked like so, @samp{octave:13>}, |
| 3294 | 76 are lines you type, ending each with a carriage return. Octave will |
| 77 respond with an answer, or by displaying a graph. | |
| 78 | |
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79 @subsection Elementary Calculations |
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80 |
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81 Octave can easily be used for basic numerical calculations. Octave |
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82 knows about arithmetic operations (+,-,*,/), exponentiation (^), |
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83 natural logarithms/exponents (log, exp), and the trigonometric |
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84 functions (sin, cos, @dots{}). Moreover, Octave calculations work |
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85 on real or imaginary numbers (i,j). In addition, some mathematical |
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86 constants such as the base of the natural logarithm (e) and the ratio |
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87 of a circle's circumference to its diameter (pi) are pre-defined. |
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88 |
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89 @noindent |
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90 For example, to verify Euler's Identity, |
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91 @tex |
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92 $$e^{\imath\pi} = -1$$ |
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93 @end tex |
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94 @ifnottex |
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95 @display |
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96 |
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97 i*pi |
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98 e = -1 |
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99 @end display |
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100 @end ifnottex |
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101 |
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102 @noindent |
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103 type the following which will evaluate to @code{-1} within the |
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104 tolerance of the calculation. |
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105 |
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106 @example |
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107 octave:1> exp(i*pi) |
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108 @end example |
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109 |
| 6623 | 110 @subsection Creating a Matrix |
| 3294 | 111 |
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112 Vectors and matrices are the basic building blocks for numerical analysis. |
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113 To create a new matrix and store it in a variable so that you can |
| 3294 | 114 refer to it later, type the command |
| 115 | |
| 116 @example | |
| 6620 | 117 octave:1> A = [ 1, 1, 2; 3, 5, 8; 13, 21, 34 ] |
| 3294 | 118 @end example |
| 119 | |
| 120 @noindent | |
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121 Octave will respond by printing the matrix in neatly aligned columns. |
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122 Octave uses a comma or space to separate entries in a row, and a |
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123 semicolon or carriage return to separate one row from the next. |
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124 Ending a command with a semicolon tells Octave not to print the result |
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125 of the command. For example, |
| 3294 | 126 |
| 127 @example | |
| 6620 | 128 octave:2> B = rand (3, 2); |
| 3294 | 129 @end example |
| 130 | |
| 131 @noindent | |
| 132 will create a 3 row, 2 column matrix with each element set to a random | |
| 133 value between zero and one. | |
| 134 | |
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135 To display the value of a variable, simply type the name of the |
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136 variable at the prompt. For example, to display the value stored in the |
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137 matrix @code{B}, type the command |
| 3294 | 138 |
| 139 @example | |
| 6620 | 140 octave:3> B |
| 3294 | 141 @end example |
| 142 | |
| 6623 | 143 @subsection Matrix Arithmetic |
| 3294 | 144 |
| 145 Octave has a convenient operator notation for performing matrix | |
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146 arithmetic. For example, to multiply the matrix @code{A} by a scalar |
| 3294 | 147 value, type the command |
| 148 | |
| 149 @example | |
| 6620 | 150 octave:4> 2 * A |
| 3294 | 151 @end example |
| 152 | |
| 6620 | 153 @noindent |
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154 To multiply the two matrices @code{A} and @code{B}, type the command |
| 3294 | 155 |
| 156 @example | |
| 6620 | 157 octave:5> A * B |
| 3294 | 158 @end example |
| 159 | |
| 6620 | 160 @noindent |
| 161 and to form the matrix product | |
| 3294 | 162 @tex |
| 6620 | 163 $@code{A}^T@code{A}$, |
| 3294 | 164 @end tex |
| 6620 | 165 @ifnottex |
| 166 @code{transpose (A) * A}, | |
| 167 @end ifnottex | |
| 3294 | 168 type the command |
| 169 | |
| 170 @example | |
| 6620 | 171 octave:6> A' * A |
| 3294 | 172 @end example |
| 173 | |
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174 @subsection Solving Systems of Linear Equations |
| 3294 | 175 |
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176 Systems of linear equations are ubiquitous in numerical analysis. |
| 6620 | 177 To solve the set of linear equations @code{A@var{x} = b}, |
| 3294 | 178 use the left division operator, @samp{\}: |
| 179 | |
| 180 @example | |
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181 @var{x} = A \ b |
| 3294 | 182 @end example |
| 183 | |
| 184 @noindent | |
| 185 This is conceptually equivalent to | |
| 186 @tex | |
| 6620 | 187 $@code{A}^{-1}@code{b}$, |
| 3294 | 188 @end tex |
| 6620 | 189 @ifnottex |
| 3294 | 190 @code{inv (a) * b}, |
| 6620 | 191 @end ifnottex |
| 3294 | 192 but avoids computing the inverse of a matrix directly. |
| 193 | |
| 194 If the coefficient matrix is singular, Octave will print a warning | |
| 195 message and compute a minimum norm solution. | |
| 196 | |
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197 A simple example comes from chemistry and the need to obtain balanced |
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198 chemical equations. Consider the burning of hydrogen and oxygen to |
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199 produce water. |
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200 @tex |
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201 $$ {\rm H_{2}} + {\rm O_{2}} \rightarrow {\rm H_{2}O} $$ |
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202 @end tex |
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203 @ifnottex |
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204 |
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205 @example |
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206 H2 + O2 --> H2O |
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207 @end example |
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208 |
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209 @end ifnottex |
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210 @noindent |
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211 The equation above is not accurate. The Law of Conservation of Mass requires |
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212 that the number of molecules of each type balance on the left- and right-hand |
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213 sides of the equation. Writing the variable overall reaction with |
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214 individual equations for hydrogen and oxygen one finds: |
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215 @tex |
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216 \vbox{ |
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217 $$ x_{1}{\rm H_{2}} + x_{2}{\rm O_{2}} \rightarrow {\rm H_{2}O} $$ |
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218 $$ {\rm H:}\quad 2x_{1} + 0x_{2} \rightarrow 2 $$ |
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219 $$ {\rm O:}\quad 0x_{1} + 2x_{2} \rightarrow 1 $$ |
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220 } |
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221 @end tex |
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222 @ifnottex |
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223 |
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224 @example |
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225 @group |
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226 x1*H2 + x2*O2 --> H2O |
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227 H: 2*x1 + 0*x2 --> 2 |
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228 O: 0*x1 + 2*x2 --> 1 |
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229 @end group |
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230 @end example |
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231 |
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232 @end ifnottex |
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233 @noindent |
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234 The solution in Octave is found in just three steps. |
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235 |
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236 @example |
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237 @group |
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238 octave:1> A = [ 2, 0; 0, 2 ]; |
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239 octave:2> b = [ 2; 1 ]; |
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240 octave:3> x = A \ b |
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241 @end group |
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242 @end example |
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243 |
| 6623 | 244 @subsection Integrating Differential Equations |
| 3294 | 245 |
| 246 Octave has built-in functions for solving nonlinear differential | |
| 247 equations of the form | |
| 248 @tex | |
| 249 $$ | |
| 250 {dx \over dt} = f(x,t), \qquad x(t=t_0) = x_0 | |
| 251 $$ | |
| 252 @end tex | |
| 6620 | 253 @ifnottex |
| 3294 | 254 |
| 255 @example | |
| 256 @group | |
| 257 dx | |
| 258 -- = f (x, t) | |
| 259 dt | |
| 260 @end group | |
| 261 @end example | |
| 262 | |
| 263 @noindent | |
| 264 with the initial condition | |
| 265 | |
| 266 @example | |
| 267 x(t = t0) = x0 | |
| 268 @end example | |
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269 |
| 6620 | 270 @end ifnottex |
| 3294 | 271 @noindent |
| 272 For Octave to integrate equations of this form, you must first provide a | |
| 273 definition of the function | |
| 274 @tex | |
| 275 $f (x, t)$. | |
| 276 @end tex | |
| 6620 | 277 @ifnottex |
| 3294 | 278 @code{f(x,t)}. |
| 6620 | 279 @end ifnottex |
| 3294 | 280 This is straightforward, and may be accomplished by entering the |
| 281 function body directly on the command line. For example, the following | |
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282 commands define the right-hand side function for an interesting pair of |
| 3294 | 283 nonlinear differential equations. Note that while you are entering a |
| 284 function, Octave responds with a different prompt, to indicate that it | |
| 285 is waiting for you to complete your input. | |
| 286 | |
| 287 @example | |
| 288 @group | |
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289 octave:1> function xdot = f (x, t) |
| 3294 | 290 > |
| 291 > r = 0.25; | |
| 292 > k = 1.4; | |
| 293 > a = 1.5; | |
| 294 > b = 0.16; | |
| 295 > c = 0.9; | |
| 296 > d = 0.8; | |
| 297 > | |
| 298 > xdot(1) = r*x(1)*(1 - x(1)/k) - a*x(1)*x(2)/(1 + b*x(1)); | |
| 299 > xdot(2) = c*a*x(1)*x(2)/(1 + b*x(1)) - d*x(2); | |
| 300 > | |
| 301 > endfunction | |
| 302 @end group | |
| 303 @end example | |
| 304 | |
| 305 @noindent | |
| 306 Given the initial condition | |
| 307 | |
| 308 @example | |
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309 octave:2> x0 = [1; 2]; |
| 3294 | 310 @end example |
| 311 | |
| 312 @noindent | |
| 313 and the set of output times as a column vector (note that the first | |
| 314 output time corresponds to the initial condition given above) | |
| 315 | |
| 316 @example | |
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317 octave:3> t = linspace (0, 50, 200)'; |
| 3294 | 318 @end example |
| 319 | |
| 320 @noindent | |
| 321 it is easy to integrate the set of differential equations: | |
| 322 | |
| 323 @example | |
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324 octave:4> x = lsode ("f", x0, t); |
| 3294 | 325 @end example |
| 326 | |
| 327 @noindent | |
| 328 The function @code{lsode} uses the Livermore Solver for Ordinary | |
| 329 Differential Equations, described in A. C. Hindmarsh, @cite{ODEPACK, a | |
| 330 Systematized Collection of ODE Solvers}, in: Scientific Computing, R. S. | |
| 331 Stepleman et al. (Eds.), North-Holland, Amsterdam, 1983, pages 55--64. | |
| 332 | |
| 6623 | 333 @subsection Producing Graphical Output |
| 3294 | 334 |
| 335 To display the solution of the previous example graphically, use the | |
| 336 command | |
| 337 | |
| 338 @example | |
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339 octave:1> plot (t, x) |
| 3294 | 340 @end example |
| 341 | |
| 6620 | 342 @noindent |
| 343 If you are using a graphical user interface, Octave will automatically create | |
| 6331 | 344 a separate window to display the plot. |
| 345 | |
| 6620 | 346 To save a plot once it has been displayed on the screen, use the print |
| 6331 | 347 command. For example, |
| 3294 | 348 |
| 349 @example | |
| 6331 | 350 print -deps foo.eps |
| 3294 | 351 @end example |
| 352 | |
| 353 @noindent | |
| 7001 | 354 will create a file called @file{foo.eps} that contains a rendering of |
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355 the current plot in Encapsulated PostScript format. The command |
| 3294 | 356 |
| 357 @example | |
| 6331 | 358 help print |
| 3294 | 359 @end example |
| 360 | |
| 361 @noindent | |
| 6331 | 362 explains more options for the @code{print} command and provides a list |
| 6620 | 363 of additional output file formats. |
| 3294 | 364 |
| 6623 | 365 @subsection Editing What You Have Typed |
| 3294 | 366 |
| 367 At the Octave prompt, you can recall, edit, and reissue previous | |
| 368 commands using Emacs- or vi-style editing commands. The default | |
| 369 keybindings use Emacs-style commands. For example, to recall the | |
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370 previous command, press @kbd{Control-p} (written @kbd{C-p} for |
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371 short). Doing this will normally bring back the previous line of input. |
| 6620 | 372 @kbd{C-n} will bring up the next line of input, @kbd{C-b} will move |
| 373 the cursor backward on the line, @kbd{C-f} will move the cursor forward | |
| 374 on the line, etc. | |
| 3294 | 375 |
| 376 A complete description of the command line editing capability is given | |
| 377 in this manual in @ref{Command Line Editing}. | |
| 378 | |
| 6623 | 379 @subsection Help and Documentation |
| 3294 | 380 |
| 381 Octave has an extensive help facility. The same documentation that is | |
| 382 available in printed form is also available from the Octave prompt, | |
| 383 because both forms of the documentation are created from the same input | |
| 384 file. | |
| 385 | |
| 386 In order to get good help you first need to know the name of the command | |
| 387 that you want to use. This name of the function may not always be | |
| 388 obvious, but a good place to start is to just type @code{help}. | |
| 389 This will show you all the operators, reserved words, functions, | |
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390 built-in variables, and function files. An alternative is to search the |
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391 documentation using the @code{lookfor} function. This function is |
| 6620 | 392 described in @ref{Getting Help}. |
| 393 | |
| 394 Once you know the name of the function you wish to use, you can get more | |
| 395 help on the function by simply including the name as an argument to help. | |
| 396 For example, | |
| 3294 | 397 |
| 398 @example | |
| 399 help plot | |
| 400 @end example | |
| 401 | |
| 402 @noindent | |
| 403 will display the help text for the @code{plot} function. | |
| 404 | |
| 405 Octave sends output that is too long to fit on one screen through a | |
| 406 pager like @code{less} or @code{more}. Type a @key{RET} to advance one | |
| 407 line, a @key{SPC} to advance one page, and @key{q} to exit the pager. | |
| 408 | |
| 409 The part of Octave's help facility that allows you to read the complete | |
| 410 text of the printed manual from within Octave normally uses a separate | |
| 411 program called Info. When you invoke Info you will be put into a menu | |
| 412 driven program that contains the entire Octave manual. Help for using | |
| 413 Info is provided in this manual in @ref{Getting Help}. | |
| 414 | |
| 4167 | 415 @node Conventions |
| 3294 | 416 @section Conventions |
| 417 | |
| 418 This section explains the notational conventions that are used in this | |
| 419 manual. You may want to skip this section and refer back to it later. | |
| 420 | |
| 421 @menu | |
| 422 * Fonts:: | |
| 423 * Evaluation Notation:: | |
| 424 * Printing Notation:: | |
| 425 * Error Messages:: | |
| 426 * Format of Descriptions:: | |
| 427 @end menu | |
| 428 | |
| 4167 | 429 @node Fonts |
| 3294 | 430 @subsection Fonts |
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431 @cindex documentation fonts |
| 3294 | 432 |
| 433 Examples of Octave code appear in this font or form: @code{svd (a)}. | |
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434 Names that represent variables or function arguments appear |
| 3294 | 435 in this font or form: @var{first-number}. Commands that you type at the |
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436 shell prompt appear in this font or form: @samp{octave --no-init-file}. |
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437 Commands that you type at the Octave prompt sometimes appear in this font |
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438 or form: @kbd{foo --bar --baz}. Specific keys on your keyboard appear |
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439 in this font or form: @key{ANY}. |
| 3294 | 440 |
| 4167 | 441 @node Evaluation Notation |
| 3294 | 442 @subsection Evaluation Notation |
| 443 @cindex evaluation notation | |
| 444 @cindex documentation notation | |
| 445 | |
| 446 In the examples in this manual, results from expressions that you | |
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447 evaluate are indicated with @samp{@result{}}. For example: |
| 3294 | 448 |
| 449 @example | |
| 450 @group | |
| 451 sqrt (2) | |
| 452 @result{} 1.4142 | |
| 453 @end group | |
| 454 @end example | |
| 455 | |
| 456 @noindent | |
| 457 You can read this as ``@code{sqrt (2)} evaluates to 1.4142''. | |
| 458 | |
| 459 In some cases, matrix values that are returned by expressions are | |
| 460 displayed like this | |
| 461 | |
| 462 @example | |
| 463 @group | |
| 464 [1, 2; 3, 4] == [1, 3; 2, 4] | |
| 465 @result{} [ 1, 0; 0, 1 ] | |
| 466 @end group | |
| 467 @end example | |
| 468 | |
| 469 @noindent | |
| 470 and in other cases, they are displayed like this | |
| 471 | |
| 472 @example | |
| 473 @group | |
| 474 eye (3) | |
| 475 @result{} 1 0 0 | |
| 476 0 1 0 | |
| 477 0 0 1 | |
| 478 @end group | |
| 479 @end example | |
| 480 | |
| 481 @noindent | |
| 482 in order to clearly show the structure of the result. | |
| 483 | |
| 484 Sometimes to help describe one expression, another expression is | |
| 485 shown that produces identical results. The exact equivalence of | |
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486 expressions is indicated with @samp{@equiv{}}. For example: |
| 3294 | 487 |
| 488 @example | |
| 489 @group | |
| 490 rot90 ([1, 2; 3, 4], -1) | |
| 491 @equiv{} | |
| 492 rot90 ([1, 2; 3, 4], 3) | |
| 493 @equiv{} | |
| 494 rot90 ([1, 2; 3, 4], 7) | |
| 495 @end group | |
| 496 @end example | |
| 497 | |
| 4167 | 498 @node Printing Notation |
| 3294 | 499 @subsection Printing Notation |
| 500 @cindex printing notation | |
| 501 | |
| 502 Many of the examples in this manual print text when they are | |
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503 evaluated. In this manual the printed text resulting from an example |
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504 is indicated by @samp{@print{}}. The value that is returned by |
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505 evaluating the expression is displayed with @samp{@result{}} |
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506 (@code{1} in the next example) and follows on a separate line. |
| 3294 | 507 |
| 508 @example | |
| 509 @group | |
| 510 printf ("foo %s\n", "bar") | |
| 511 @print{} foo bar | |
| 512 @result{} 1 | |
| 513 @end group | |
| 514 @end example | |
| 515 | |
| 4167 | 516 @node Error Messages |
| 3294 | 517 @subsection Error Messages |
| 518 @cindex error message notation | |
| 519 | |
| 520 Some examples signal errors. This normally displays an error message | |
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521 on your terminal. Error messages are shown on a line beginning with |
| 3294 | 522 @code{error:}. |
| 523 | |
| 524 @example | |
| 525 @group | |
| 7490 | 526 fieldnames ([1, 2; 3, 4]) |
| 527 error: fieldnames: wrong type argument `matrix' | |
| 3294 | 528 @end group |
| 529 @end example | |
| 530 | |
| 4167 | 531 @node Format of Descriptions |
| 3294 | 532 @subsection Format of Descriptions |
| 533 @cindex description format | |
| 534 | |
| 535 Functions, commands, and variables are described in this manual in a | |
| 536 uniform format. The first line of a description contains the name of | |
| 537 the item followed by its arguments, if any. | |
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538 @ifnottex |
| 3294 | 539 The category---function, variable, or whatever---appears at the |
| 540 beginning of the line. | |
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541 @end ifnottex |
| 3294 | 542 @iftex |
| 543 The category---function, variable, or whatever---is printed next to the | |
| 544 right margin. | |
| 545 @end iftex | |
| 546 The description follows on succeeding lines, sometimes with examples. | |
| 547 | |
| 548 @menu | |
| 549 * A Sample Function Description:: | |
| 550 * A Sample Command Description:: | |
| 551 * A Sample Variable Description:: | |
| 552 @end menu | |
| 553 | |
| 4167 | 554 @node A Sample Function Description |
| 3294 | 555 @subsubsection A Sample Function Description |
| 556 @cindex function descriptions | |
| 557 | |
| 558 In a function description, the name of the function being described | |
| 559 appears first. It is followed on the same line by a list of parameters. | |
| 560 The names used for the parameters are also used in the body of the | |
| 561 description. | |
| 562 | |
| 563 Here is a description of an imaginary function @code{foo}: | |
| 564 | |
| 565 @deftypefn {Function} {} foo (@var{x}, @var{y}, @dots{}) | |
| 566 The function @code{foo} subtracts @var{x} from @var{y}, then adds the | |
| 567 remaining arguments to the result. If @var{y} is not supplied, then the | |
| 568 number 19 is used by default. | |
| 569 | |
| 570 @example | |
| 571 @group | |
| 572 foo (1, [3, 5], 3, 9) | |
| 573 @result{} [ 14, 16 ] | |
| 574 foo (5) | |
| 575 @result{} 14 | |
| 576 @end group | |
| 577 @end example | |
| 578 | |
| 579 More generally, | |
| 580 | |
| 581 @example | |
| 582 @group | |
| 583 foo (@var{w}, @var{x}, @var{y}, @dots{}) | |
| 584 @equiv{} | |
| 585 @var{x} - @var{w} + @var{y} + @dots{} | |
| 586 @end group | |
| 587 @end example | |
| 588 @end deftypefn | |
| 589 | |
| 590 Any parameter whose name contains the name of a type (e.g., | |
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591 @var{integer} or @var{matrix}) is expected to be of that |
| 3294 | 592 type. Parameters named @var{object} may be of any type. Parameters |
| 593 with other sorts of names (e.g., @var{new_file}) are discussed | |
| 594 specifically in the description of the function. In some sections, | |
| 595 features common to parameters of several functions are described at the | |
| 596 beginning. | |
| 597 | |
| 598 Functions in Octave may be defined in several different ways. The | |
| 7001 | 599 category name for functions may include another name that indicates the |
| 3294 | 600 way that the function is defined. These additional tags include |
| 601 | |
| 602 @table @asis | |
| 6620 | 603 @item Function File |
| 604 @cindex function file | |
| 605 The function described is defined using Octave commands stored in a text | |
| 606 file. @xref{Function Files}. | |
| 607 | |
| 3294 | 608 @item Built-in Function |
| 609 @cindex built-in function | |
| 610 The function described is written in a language like C++, C, or Fortran, | |
| 611 and is part of the compiled Octave binary. | |
| 612 | |
| 613 @item Loadable Function | |
| 614 @cindex loadable function | |
| 615 The function described is written in a language like C++, C, or Fortran. | |
| 616 On systems that support dynamic linking of user-supplied functions, it | |
| 617 may be automatically linked while Octave is running, but only if it is | |
| 618 needed. @xref{Dynamically Linked Functions}. | |
| 619 | |
| 620 @item Mapping Function | |
| 621 @cindex mapping function | |
| 622 The function described works element-by-element for matrix and vector | |
| 623 arguments. | |
| 624 @end table | |
| 625 | |
| 4167 | 626 @node A Sample Command Description |
| 3294 | 627 @subsubsection A Sample Command Description |
| 628 @cindex command descriptions | |
| 629 | |
| 630 Command descriptions have a format similar to function descriptions, | |
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changeset
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631 except that the word `Function' is replaced by `Command'. Commands are |
| 7001 | 632 functions that may be called without surrounding their arguments in |
| 3294 | 633 parentheses. For example, here is the description for Octave's |
| 634 @code{cd} command: | |
| 635 | |
| 636 @deffn {Command} cd dir | |
| 637 @deffnx {Command} chdir dir | |
| 638 Change the current working directory to @var{dir}. For example, | |
| 639 @kbd{cd ~/octave} changes the current working directory to | |
| 640 @file{~/octave}. If the directory does not exist, an error message is | |
| 641 printed and the working directory is not changed. | |
| 642 @end deffn | |
| 643 | |
| 4167 | 644 @node A Sample Variable Description |
| 3294 | 645 @subsubsection A Sample Variable Description |
| 646 @cindex variable descriptions | |
| 647 | |
| 648 A @dfn{variable} is a name that can hold a value. Although any variable | |
| 649 can be set by the user, @dfn{built-in variables} typically exist | |
| 650 specifically so that users can change them to alter the way Octave | |
| 651 behaves (built-in variables are also sometimes called @dfn{user | |
| 652 options}). Ordinary variables and built-in variables are described | |
| 653 using a format like that for functions except that there are no | |
| 654 arguments. | |
| 655 | |
| 656 Here is a description of the imaginary variable | |
| 657 @code{do_what_i_mean_not_what_i_say}. | |
| 658 | |
| 659 @defvr {Built-in Variable} do_what_i_mean_not_what_i_say | |
| 660 If the value of this variable is nonzero, Octave will do what you | |
| 661 actually wanted, even if you have typed a completely different and | |
| 662 meaningless list of commands. | |
| 663 @end defvr | |
| 664 | |
| 665 Other variable descriptions have the same format, but `Built-in | |
| 666 Variable' is replaced by `Variable', for ordinary variables, or | |
| 667 `Constant' for symbolic constants whose values cannot be changed. |