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1 @c Copyright (C) 1996, 1997 John W. Eaton |
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2 @c This is part of the Octave manual. |
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3 @c For copying conditions, see the file gpl.texi. |
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4 |
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5 @node Functions and Scripts |
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6 @chapter Functions and Script Files |
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7 @cindex defining functions |
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8 @cindex user-defined functions |
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9 @cindex functions, user-defined |
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10 @cindex script files |
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11 |
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12 Complicated Octave programs can often be simplified by defining |
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13 functions. Functions can be defined directly on the command line during |
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14 interactive Octave sessions, or in external files, and can be called just |
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15 like built-in functions. |
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16 |
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17 @menu |
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18 * Defining Functions:: |
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19 * Multiple Return Values:: |
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20 * Variable-length Argument Lists:: |
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21 * Variable-length Return Lists:: |
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22 * Returning From a Function:: |
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23 * Default Arguments:: |
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24 * Function Files:: |
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25 * Script Files:: |
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26 * Dynamically Linked Functions:: |
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27 * Function Handles and Inline:: |
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28 * Organization of Functions:: |
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29 @end menu |
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30 |
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31 @node Defining Functions |
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32 @section Defining Functions |
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33 @cindex @code{function} statement |
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34 @cindex @code{endfunction} statement |
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35 |
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36 In its simplest form, the definition of a function named @var{name} |
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37 looks like this: |
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38 |
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39 @example |
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40 @group |
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41 function @var{name} |
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42 @var{body} |
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43 endfunction |
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44 @end group |
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45 @end example |
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46 |
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47 @noindent |
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48 A valid function name is like a valid variable name: a sequence of |
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49 letters, digits and underscores, not starting with a digit. Functions |
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50 share the same pool of names as variables. |
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51 |
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52 The function @var{body} consists of Octave statements. It is the |
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53 most important part of the definition, because it says what the function |
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54 should actually @emph{do}. |
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55 |
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56 For example, here is a function that, when executed, will ring the bell |
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57 on your terminal (assuming that it is possible to do so): |
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58 |
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59 @example |
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60 @group |
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61 function wakeup |
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62 printf ("\a"); |
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63 endfunction |
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64 @end group |
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65 @end example |
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66 |
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67 The @code{printf} statement (@pxref{Input and Output}) simply tells |
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68 Octave to print the string @code{"\a"}. The special character @samp{\a} |
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69 stands for the alert character (ASCII 7). @xref{Strings}. |
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70 |
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71 Once this function is defined, you can ask Octave to evaluate it by |
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72 typing the name of the function. |
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73 |
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74 Normally, you will want to pass some information to the functions you |
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75 define. The syntax for passing parameters to a function in Octave is |
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76 |
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77 @example |
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78 @group |
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79 function @var{name} (@var{arg-list}) |
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80 @var{body} |
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81 endfunction |
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82 @end group |
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83 @end example |
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84 |
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85 @noindent |
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86 where @var{arg-list} is a comma-separated list of the function's |
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87 arguments. When the function is called, the argument names are used to |
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88 hold the argument values given in the call. The list of arguments may |
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89 be empty, in which case this form is equivalent to the one shown above. |
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90 |
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91 To print a message along with ringing the bell, you might modify the |
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92 @code{wakeup} to look like this: |
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93 |
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94 @example |
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95 @group |
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96 function wakeup (message) |
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97 printf ("\a%s\n", message); |
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98 endfunction |
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99 @end group |
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100 @end example |
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101 |
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102 Calling this function using a statement like this |
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103 |
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104 @example |
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105 wakeup ("Rise and shine!"); |
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106 @end example |
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107 |
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108 @noindent |
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109 will cause Octave to ring your terminal's bell and print the message |
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110 @samp{Rise and shine!}, followed by a newline character (the @samp{\n} |
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111 in the first argument to the @code{printf} statement). |
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112 |
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113 In most cases, you will also want to get some information back from the |
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114 functions you define. Here is the syntax for writing a function that |
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115 returns a single value: |
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116 |
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117 @example |
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118 @group |
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119 function @var{ret-var} = @var{name} (@var{arg-list}) |
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120 @var{body} |
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121 endfunction |
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122 @end group |
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123 @end example |
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124 |
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125 @noindent |
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126 The symbol @var{ret-var} is the name of the variable that will hold the |
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127 value to be returned by the function. This variable must be defined |
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128 before the end of the function body in order for the function to return |
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129 a value. |
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130 |
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131 Variables used in the body of a function are local to the |
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132 function. Variables named in @var{arg-list} and @var{ret-var} are also |
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133 local to the function. @xref{Global Variables}, for information about |
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134 how to access global variables inside a function. |
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135 |
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136 For example, here is a function that computes the average of the |
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137 elements of a vector: |
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138 |
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139 @example |
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140 @group |
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141 function retval = avg (v) |
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142 retval = sum (v) / length (v); |
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143 endfunction |
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144 @end group |
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145 @end example |
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146 |
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147 If we had written @code{avg} like this instead, |
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148 |
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149 @example |
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150 @group |
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151 function retval = avg (v) |
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152 if (isvector (v)) |
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153 retval = sum (v) / length (v); |
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154 endif |
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155 endfunction |
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156 @end group |
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157 @end example |
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158 |
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159 @noindent |
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160 and then called the function with a matrix instead of a vector as the |
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161 argument, Octave would have printed an error message like this: |
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162 |
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163 @example |
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164 @group |
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165 error: `retval' undefined near line 1 column 10 |
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166 error: evaluating index expression near line 7, column 1 |
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167 @end group |
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168 @end example |
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169 |
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170 @noindent |
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171 because the body of the @code{if} statement was never executed, and |
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172 @code{retval} was never defined. To prevent obscure errors like this, |
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173 it is a good idea to always make sure that the return variables will |
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174 always have values, and to produce meaningful error messages when |
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175 problems are encountered. For example, @code{avg} could have been |
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176 written like this: |
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177 |
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178 @example |
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179 @group |
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180 function retval = avg (v) |
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181 retval = 0; |
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182 if (isvector (v)) |
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183 retval = sum (v) / length (v); |
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184 else |
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185 error ("avg: expecting vector argument"); |
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186 endif |
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187 endfunction |
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188 @end group |
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189 @end example |
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190 |
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191 There is still one additional problem with this function. What if it is |
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192 called without an argument? Without additional error checking, Octave |
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193 will probably print an error message that won't really help you track |
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194 down the source of the error. To allow you to catch errors like this, |
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195 Octave provides each function with an automatic variable called |
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196 @code{nargin}. Each time a function is called, @code{nargin} is |
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197 automatically initialized to the number of arguments that have actually |
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198 been passed to the function. For example, we might rewrite the |
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199 @code{avg} function like this: |
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200 |
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201 @example |
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202 @group |
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203 function retval = avg (v) |
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204 retval = 0; |
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205 if (nargin != 1) |
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206 usage ("avg (vector)"); |
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207 endif |
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208 if (isvector (v)) |
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209 retval = sum (v) / length (v); |
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210 else |
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211 error ("avg: expecting vector argument"); |
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212 endif |
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213 endfunction |
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214 @end group |
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215 @end example |
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216 |
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217 Although Octave does not automatically report an error if you call a |
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218 function with more arguments than expected, doing so probably indicates |
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219 that something is wrong. Octave also does not automatically report an |
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220 error if a function is called with too few arguments, but any attempt to |
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221 use a variable that has not been given a value will result in an error. |
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222 To avoid such problems and to provide useful messages, we check for both |
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223 possibilities and issue our own error message. |
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224 |
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225 @DOCSTRING(nargin) |
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226 |
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227 @DOCSTRING(silent_functions) |
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228 |
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229 @node Multiple Return Values |
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230 @section Multiple Return Values |
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231 |
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232 Unlike many other computer languages, Octave allows you to define |
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233 functions that return more than one value. The syntax for defining |
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234 functions that return multiple values is |
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235 |
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236 @example |
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237 function [@var{ret-list}] = @var{name} (@var{arg-list}) |
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238 @var{body} |
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239 endfunction |
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240 @end example |
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241 |
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242 @noindent |
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243 where @var{name}, @var{arg-list}, and @var{body} have the same meaning |
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244 as before, and @var{ret-list} is a comma-separated list of variable |
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245 names that will hold the values returned from the function. The list of |
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246 return values must have at least one element. If @var{ret-list} has |
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247 only one element, this form of the @code{function} statement is |
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248 equivalent to the form described in the previous section. |
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249 |
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250 Here is an example of a function that returns two values, the maximum |
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251 element of a vector and the index of its first occurrence in the vector. |
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252 |
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253 @example |
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254 @group |
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255 function [max, idx] = vmax (v) |
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256 idx = 1; |
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257 max = v (idx); |
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258 for i = 2:length (v) |
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259 if (v (i) > max) |
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260 max = v (i); |
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261 idx = i; |
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262 endif |
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263 endfor |
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264 endfunction |
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265 @end group |
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266 @end example |
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267 |
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268 In this particular case, the two values could have been returned as |
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269 elements of a single array, but that is not always possible or |
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270 convenient. The values to be returned may not have compatible |
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271 dimensions, and it is often desirable to give the individual return |
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272 values distinct names. |
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273 |
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274 In addition to setting @code{nargin} each time a function is called, |
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275 Octave also automatically initializes @code{nargout} to the number of |
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276 values that are expected to be returned. This allows you to write |
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277 functions that behave differently depending on the number of values that |
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278 the user of the function has requested. The implicit assignment to the |
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279 built-in variable @code{ans} does not figure in the count of output |
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280 arguments, so the value of @code{nargout} may be zero. |
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281 |
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282 The @code{svd} and @code{lu} functions are examples of built-in |
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283 functions that behave differently depending on the value of |
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284 @code{nargout}. |
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285 |
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286 It is possible to write functions that only set some return values. For |
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287 example, calling the function |
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288 |
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289 @example |
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290 function [x, y, z] = f () |
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291 x = 1; |
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292 z = 2; |
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293 endfunction |
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294 @end example |
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295 |
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296 @noindent |
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297 as |
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298 |
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299 @example |
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300 [a, b, c] = f () |
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301 @end example |
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302 |
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303 @noindent |
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304 produces: |
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305 |
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306 @example |
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307 a = 1 |
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308 |
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309 b = [](0x0) |
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310 |
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311 c = 2 |
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312 @end example |
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313 |
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314 @noindent |
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315 along with a warning. |
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316 |
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317 @DOCSTRING(nargout) |
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318 |
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319 @DOCSTRING(nargchk) |
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320 |
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321 @node Variable-length Argument Lists |
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322 @section Variable-length Argument Lists |
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323 @cindex variable-length argument lists |
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324 @cindex @code{...} |
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325 Sometimes the number of input arguments is not known when the function |
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326 is defined. As an example think of a function that returns the smallest |
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327 of all its input arguments. For example, |
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328 |
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329 @example |
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330 a = smallest (1, 2, 3); |
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331 b = smallest (1, 2, 3, 4); |
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332 @end example |
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333 |
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334 @noindent |
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335 In this example both @code{a} and @code{b} would be 1. One way to write |
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336 the @code{smallest} function is |
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337 |
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338 @example |
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339 function val = smallest (arg1, arg2, arg3, arg4, arg5) |
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340 @var{body} |
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341 endfunction |
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342 @end example |
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343 |
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344 @noindent |
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345 and then use the value of @code{nargin} to determine which of the input |
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346 arguments should be considered. The problem with this approach is |
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347 that it can only handle a limited number of input arguments. |
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348 |
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349 Octave supports the @code{varargin} keyword for handling a variable |
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350 number of input arguments. Using @code{varargin} the function |
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351 looks like this |
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352 |
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353 @example |
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354 function val = smallest (varargin) |
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355 @var{body} |
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356 endfunction |
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357 @end example |
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358 |
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359 @noindent |
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360 In the function body the input arguments can be accessed through the |
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361 variable @code{varargin}. This variable is a cell array containing |
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362 all the input arguments. @xref{Cell Arrays}, for details on working |
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363 with cell arrays. The @code{smallest} function can now be defined |
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364 like this |
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365 |
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366 @example |
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367 function val = smallest (varargin) |
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368 val = min ([varargin@{:@}]); |
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369 endfunction |
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370 @end example |
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371 |
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372 @noindent |
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373 This implementation handles any number of input arguments, but it's also |
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374 a very simple solution to the problem. |
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375 |
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376 A slightly more complex example of @code{varargin} is a function |
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377 @code{print_arguments} that prints all input arguments. Such a function |
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378 can be defined like this |
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379 |
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380 @example |
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381 function print_arguments (varargin) |
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382 for i = 1:length (varargin) |
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383 printf ("Input argument %d: ", i); |
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384 disp (varargin@{i@}); |
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385 endfor |
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386 endfunction |
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387 @end example |
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388 |
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389 @noindent |
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390 This function produces output like this |
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391 |
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392 @example |
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393 @group |
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394 print_arguments (1, "two", 3); |
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395 @print{} Input argument 1: 1 |
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396 @print{} Input argument 2: two |
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397 @print{} Input argument 3: 3 |
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398 @end group |
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399 @end example |
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400 |
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401 @node Variable-length Return Lists |
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402 @section Variable-length Return Lists |
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403 @cindex variable-length return lists |
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404 It is possible to return a variable number of output arguments from a |
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405 function using a syntax that's similar to the one used with the |
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406 @code{varargin} keyword. To let a function return a variable number of |
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407 output arguments the @code{varargout} keyword is used. As with |
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408 @code{varargin} @code{varargout} is a cell array that will contain the |
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409 requested output arguments. |
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410 |
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411 As an example the following function sets the first output argument to |
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412 1, the second to 2, and so on. |
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413 |
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414 @example |
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415 function varargout = one_to_n () |
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416 for i = 1:nargout |
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417 varargout@{i@} = i; |
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418 endfor |
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419 endfunction |
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420 @end example |
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421 |
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422 @noindent |
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423 When called this function returns values like this |
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424 |
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425 @example |
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426 @group |
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427 [a, b, c] = one_to_n () |
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428 @result{} a = 1 |
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429 @result{} b = 2 |
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430 @result{} c = 3 |
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431 @end group |
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432 @end example |
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433 |
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434 @node Returning From a Function |
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435 @section Returning From a Function |
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436 |
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437 The body of a user-defined function can contain a @code{return} statement. |
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438 This statement returns control to the rest of the Octave program. It |
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439 looks like this: |
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440 |
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441 @example |
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442 return |
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443 @end example |
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444 |
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445 Unlike the @code{return} statement in C, Octave's @code{return} |
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446 statement cannot be used to return a value from a function. Instead, |
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447 you must assign values to the list of return variables that are part of |
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448 the @code{function} statement. The @code{return} statement simply makes |
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449 it easier to exit a function from a deeply nested loop or conditional |
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450 statement. |
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451 |
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452 Here is an example of a function that checks to see if any elements of a |
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453 vector are nonzero. |
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454 |
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455 @example |
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456 @group |
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457 function retval = any_nonzero (v) |
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458 retval = 0; |
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459 for i = 1:length (v) |
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460 if (v (i) != 0) |
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461 retval = 1; |
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462 return; |
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463 endif |
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464 endfor |
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465 printf ("no nonzero elements found\n"); |
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466 endfunction |
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467 @end group |
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468 @end example |
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469 |
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470 Note that this function could not have been written using the |
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471 @code{break} statement to exit the loop once a nonzero value is found |
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472 without adding extra logic to avoid printing the message if the vector |
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473 does contain a nonzero element. |
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474 |
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475 @deffn {Keyword} return |
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476 When Octave encounters the keyword @code{return} inside a function or |
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477 script, it returns control to the caller immediately. At the top level, |
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478 the return statement is ignored. A @code{return} statement is assumed |
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479 at the end of every function definition. |
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480 @end deffn |
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481 |
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482 @DOCSTRING(return_last_computed_value) |
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483 |
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484 @node Default Arguments |
|
|
485 @section Default Arguments |
|
|
486 @cindex default arguments |
|
|
487 |
|
|
488 Since Octave supports variable number of input arguments, it is very useful |
|
|
489 to assign default values to some input arguments. When an input argument |
|
|
490 is declared in the argument list it is possible to assign a default |
|
|
491 value to the argument like this |
|
|
492 |
|
|
493 @example |
|
|
494 function @var{name} (@var{arg1} = @var{val1}, @dots{}) |
|
|
495 @var{body} |
|
|
496 endfunction |
|
|
497 @end example |
|
|
498 |
|
|
499 @noindent |
|
|
500 If no value is assigned to @var{arg1} by the user, it will have the |
|
|
501 value @var{val1}. |
|
|
502 |
|
|
503 As an example, the following function implements a variant of the classic |
|
|
504 ``Hello, World'' program. |
|
|
505 @example |
|
|
506 function hello (who = "World") |
|
|
507 printf ("Hello, %s!\n", who); |
|
|
508 endfunction |
|
|
509 @end example |
|
|
510 |
|
|
511 @noindent |
|
|
512 When called without an input argument the function prints the following |
|
|
513 @example |
|
|
514 @group |
|
|
515 hello (); |
|
|
516 @print{} Hello, World! |
|
|
517 @end group |
|
|
518 @end example |
|
|
519 |
|
|
520 @noindent |
|
|
521 and when it's called with an input argument it prints the following |
|
|
522 @example |
|
|
523 @group |
|
|
524 hello ("Beautiful World of Free Software"); |
|
|
525 @print{} Hello, Beautiful World of Free Software! |
|
|
526 @end group |
|
|
527 @end example |
|
|
528 |
|
|
529 Sometimes it is useful to explicitly tell Octave to use the default value |
|
|
530 of an input argument. This can be done writing a @samp{:} as the value |
|
|
531 of the input argument when calling the function. |
|
|
532 @example |
|
|
533 @group |
|
|
534 hello (:); |
|
|
535 @print{} Hello, World! |
|
|
536 @end group |
|
|
537 @end example |
|
|
538 |
|
4167
|
539 @node Function Files |
|
3294
|
540 @section Function Files |
|
|
541 @cindex function file |
|
|
542 |
|
|
543 Except for simple one-shot programs, it is not practical to have to |
|
|
544 define all the functions you need each time you need them. Instead, you |
|
|
545 will normally want to save them in a file so that you can easily edit |
|
|
546 them, and save them for use at a later time. |
|
|
547 |
|
|
548 Octave does not require you to load function definitions from files |
|
|
549 before using them. You simply need to put the function definitions in a |
|
|
550 place where Octave can find them. |
|
|
551 |
|
|
552 When Octave encounters an identifier that is undefined, it first looks |
|
|
553 for variables or functions that are already compiled and currently |
|
|
554 listed in its symbol table. If it fails to find a definition there, it |
|
6477
|
555 searches the list of directories specified by the internal variable |
|
3294
|
556 @code{LOADPATH} for files ending in @file{.m} that have the same base |
|
|
557 name as the undefined identifier.@footnote{The @samp{.m} suffix was |
|
|
558 chosen for compatibility with @sc{Matlab}.} Once Octave finds a file |
|
|
559 with a name that matches, the contents of the file are read. If it |
|
|
560 defines a @emph{single} function, it is compiled and executed. |
|
|
561 @xref{Script Files}, for more information about how you can define more |
|
|
562 than one function in a single file. |
|
|
563 |
|
|
564 When Octave defines a function from a function file, it saves the full |
|
|
565 name of the file it read and the time stamp on the file. After |
|
|
566 that, it checks the time stamp on the file every time it needs the |
|
|
567 function. If the time stamp indicates that the file has changed since |
|
|
568 the last time it was read, Octave reads it again. |
|
|
569 |
|
|
570 Checking the time stamp allows you to edit the definition of a function |
|
|
571 while Octave is running, and automatically use the new function |
|
|
572 definition without having to restart your Octave session. Checking the |
|
|
573 time stamp every time a function is used is rather inefficient, but it |
|
|
574 has to be done to ensure that the correct function definition is used. |
|
|
575 |
|
|
576 To avoid degrading performance unnecessarily by checking the time stamps |
|
|
577 on functions that are not likely to change, Octave assumes that function |
|
|
578 files in the directory tree |
|
|
579 @file{@var{octave-home}/share/octave/@var{version}/m} |
|
|
580 will not change, so it doesn't have to check their time stamps every time the |
|
|
581 functions defined in those files are used. This is normally a very good |
|
|
582 assumption and provides a significant improvement in performance for the |
|
|
583 function files that are distributed with Octave. |
|
|
584 |
|
|
585 If you know that your own function files will not change while you are |
|
|
586 running Octave, you can improve performance by setting the variable |
|
|
587 @code{ignore_function_time_stamp} to @code{"all"}, so that Octave will |
|
|
588 ignore the time stamps for all function files. Setting it to |
|
|
589 @code{"system"} gives the default behavior. If you set it to anything |
|
|
590 else, Octave will check the time stamps on all function files. |
|
|
591 |
|
5775
|
592 @c FIXME -- note about time stamps on files in NFS environments? |
|
3294
|
593 |
|
6502
|
594 @DOCSTRING(addpath) |
|
|
595 |
|
|
596 @DOCSTRING(genpath) |
|
|
597 |
|
|
598 @DOCSTRING(rmpath) |
|
|
599 |
|
|
600 @DOCSTRING(savepath) |
|
|
601 |
|
6477
|
602 @DOCSTRING(path) |
|
3294
|
603 |
|
6502
|
604 @DOCSTRING(pathdef) |
|
|
605 |
|
|
606 @DOCSTRING(pathsep) |
|
|
607 |
|
3428
|
608 @DOCSTRING(rehash) |
|
|
609 |
|
|
610 @DOCSTRING(file_in_loadpath) |
|
|
611 |
|
3371
|
612 @DOCSTRING(ignore_function_time_stamp) |
|
3294
|
613 |
|
4167
|
614 @node Script Files |
|
3294
|
615 @section Script Files |
|
|
616 |
|
|
617 A script file is a file containing (almost) any sequence of Octave |
|
|
618 commands. It is read and evaluated just as if you had typed each |
|
|
619 command at the Octave prompt, and provides a convenient way to perform a |
|
|
620 sequence of commands that do not logically belong inside a function. |
|
|
621 |
|
|
622 Unlike a function file, a script file must @emph{not} begin with the |
|
|
623 keyword @code{function}. If it does, Octave will assume that it is a |
|
|
624 function file, and that it defines a single function that should be |
|
|
625 evaluated as soon as it is defined. |
|
|
626 |
|
|
627 A script file also differs from a function file in that the variables |
|
|
628 named in a script file are not local variables, but are in the same |
|
|
629 scope as the other variables that are visible on the command line. |
|
|
630 |
|
|
631 Even though a script file may not begin with the @code{function} |
|
|
632 keyword, it is possible to define more than one function in a single |
|
|
633 script file and load (but not execute) all of them at once. To do |
|
|
634 this, the first token in the file (ignoring comments and other white |
|
|
635 space) must be something other than @code{function}. If you have no |
|
|
636 other statements to evaluate, you can use a statement that has no |
|
|
637 effect, like this: |
|
|
638 |
|
|
639 @example |
|
|
640 @group |
|
|
641 # Prevent Octave from thinking that this |
|
|
642 # is a function file: |
|
|
643 |
|
|
644 1; |
|
|
645 |
|
|
646 # Define function one: |
|
|
647 |
|
|
648 function one () |
|
|
649 ... |
|
|
650 @end group |
|
|
651 @end example |
|
|
652 |
|
|
653 To have Octave read and compile these functions into an internal form, |
|
6477
|
654 you need to make sure that the file is in Octave's @code{LOADPATH} |
|
|
655 (accessible through the @code{path} function), then simply type the |
|
|
656 base name of the file that contains the commands. (Octave uses the |
|
|
657 same rules to search for script files as it does to search for |
|
|
658 function files.) |
|
3294
|
659 |
|
|
660 If the first token in a file (ignoring comments) is @code{function}, |
|
|
661 Octave will compile the function and try to execute it, printing a |
|
|
662 message warning about any non-whitespace characters that appear after |
|
|
663 the function definition. |
|
|
664 |
|
|
665 Note that Octave does not try to look up the definition of any identifier |
|
|
666 until it needs to evaluate it. This means that Octave will compile the |
|
|
667 following statements if they appear in a script file, or are typed at |
|
|
668 the command line, |
|
|
669 |
|
|
670 @example |
|
|
671 @group |
|
|
672 # not a function file: |
|
|
673 1; |
|
|
674 function foo () |
|
|
675 do_something (); |
|
|
676 endfunction |
|
|
677 function do_something () |
|
|
678 do_something_else (); |
|
|
679 endfunction |
|
|
680 @end group |
|
|
681 @end example |
|
|
682 |
|
|
683 @noindent |
|
|
684 even though the function @code{do_something} is not defined before it is |
|
|
685 referenced in the function @code{foo}. This is not an error because |
|
|
686 Octave does not need to resolve all symbols that are referenced by a |
|
|
687 function until the function is actually evaluated. |
|
|
688 |
|
|
689 Since Octave doesn't look for definitions until they are needed, the |
|
|
690 following code will always print @samp{bar = 3} whether it is typed |
|
|
691 directly on the command line, read from a script file, or is part of a |
|
|
692 function body, even if there is a function or script file called |
|
6477
|
693 @file{bar.m} in Octave's path. |
|
3294
|
694 |
|
|
695 @example |
|
|
696 @group |
|
|
697 eval ("bar = 3"); |
|
|
698 bar |
|
|
699 @end group |
|
|
700 @end example |
|
|
701 |
|
|
702 Code like this appearing within a function body could fool Octave if |
|
|
703 definitions were resolved as the function was being compiled. It would |
|
|
704 be virtually impossible to make Octave clever enough to evaluate this |
|
|
705 code in a consistent fashion. The parser would have to be able to |
|
|
706 perform the call to @code{eval} at compile time, and that would be |
|
|
707 impossible unless all the references in the string to be evaluated could |
|
|
708 also be resolved, and requiring that would be too restrictive (the |
|
|
709 string might come from user input, or depend on things that are not |
|
|
710 known until the function is evaluated). |
|
|
711 |
|
|
712 Although Octave normally executes commands from script files that have |
|
|
713 the name @file{@var{file}.m}, you can use the function @code{source} to |
|
|
714 execute commands from any file. |
|
|
715 |
|
3371
|
716 @DOCSTRING(source) |
|
3294
|
717 |
|
4167
|
718 @node Dynamically Linked Functions |
|
3294
|
719 @section Dynamically Linked Functions |
|
|
720 @cindex dynamic linking |
|
|
721 |
|
|
722 On some systems, Octave can dynamically load and execute functions |
|
|
723 written in C++. Octave can only directly call functions written in C++, |
|
|
724 but you can also load functions written in other languages |
|
|
725 by calling them from a simple wrapper function written in C++. |
|
|
726 |
|
|
727 Here is an example of how to write a C++ function that Octave can load, |
|
|
728 with commentary. The source for this function is included in the source |
|
|
729 distributions of Octave, in the file @file{examples/oregonator.cc}. It |
|
|
730 defines the same set of differential equations that are used in the |
|
|
731 example problem of @ref{Ordinary Differential Equations}. By running |
|
|
732 that example and this one, we can compare the execution times to see |
|
|
733 what sort of increase in speed you can expect by using dynamically |
|
|
734 linked functions. |
|
|
735 |
|
|
736 The function defined in @file{oregonator.cc} contains just 8 statements, |
|
|
737 and is not much different than the code defined in the corresponding |
|
|
738 M-file (also distributed with Octave in the file |
|
|
739 @file{examples/oregonator.m}). |
|
|
740 |
|
|
741 Here is the complete text of @file{oregonator.cc}: |
|
|
742 |
|
|
743 @example |
|
|
744 @group |
|
|
745 #include <octave/oct.h> |
|
|
746 |
|
|
747 DEFUN_DLD (oregonator, args, , |
|
|
748 "The `oregonator'.") |
|
|
749 @{ |
|
|
750 ColumnVector dx (3); |
|
|
751 |
|
3760
|
752 ColumnVector x (args(0).vector_value ()); |
|
3294
|
753 |
|
|
754 dx(0) = 77.27 * (x(1) - x(0)*x(1) + x(0) |
|
|
755 - 8.375e-06*pow (x(0), 2)); |
|
|
756 |
|
|
757 dx(1) = (x(2) - x(0)*x(1) - x(1)) / 77.27; |
|
|
758 |
|
|
759 dx(2) = 0.161*(x(0) - x(2)); |
|
|
760 |
|
|
761 return octave_value (dx); |
|
|
762 @} |
|
|
763 @end group |
|
|
764 @end example |
|
|
765 |
|
|
766 The first line of the file, |
|
|
767 |
|
|
768 @example |
|
|
769 #include <octave/oct.h> |
|
|
770 @end example |
|
|
771 |
|
|
772 @noindent |
|
|
773 includes declarations for all of Octave's internal functions that you |
|
|
774 will need. If you need other functions from the standard C++ or C |
|
|
775 libraries, you can include the necessary headers here. |
|
|
776 |
|
|
777 The next two lines |
|
|
778 @example |
|
|
779 @group |
|
|
780 DEFUN_DLD (oregonator, args, , |
|
|
781 "The `oregonator'.") |
|
|
782 @end group |
|
|
783 @end example |
|
|
784 |
|
|
785 @noindent |
|
|
786 declares the function. The macro @code{DEFUN_DLD} and the macros that |
|
|
787 it depends on are defined in the files @file{defun-dld.h}, |
|
|
788 @file{defun.h}, and @file{defun-int.h} (these files are included in the |
|
|
789 header file @file{octave/oct.h}). |
|
|
790 |
|
|
791 Note that the third parameter to @code{DEFUN_DLD} (@code{nargout}) is |
|
3686
|
792 not used, so it is omitted from the list of arguments in order to |
|
|
793 avoid the warning from gcc about an unused function parameter. |
|
|
794 |
|
|
795 The next line, |
|
|
796 |
|
|
797 @example |
|
|
798 ColumnVector dx (3); |
|
|
799 @end example |
|
3294
|
800 |
|
|
801 @noindent |
|
|
802 simply declares an object to store the right hand sides of the |
|
3686
|
803 differential equation, and the statement |
|
3294
|
804 |
|
|
805 @example |
|
3760
|
806 ColumnVector x (args(0).vector_value ()); |
|
3294
|
807 @end example |
|
|
808 |
|
|
809 @noindent |
|
3760
|
810 extracts a vector from the first input argument. The |
|
|
811 @code{vector_value} method is used so that the user of the function |
|
|
812 can pass either a row or column vector. The @code{ColumnVector} |
|
|
813 constructor is needed because the ODE class requires a column |
|
|
814 vector. The variable @code{args} is passed to functions defined with |
|
|
815 @code{DEFUN_DLD} as an @code{octave_value_list} object, which includes |
|
|
816 methods for getting the length of the list and extracting individual |
|
|
817 elements. |
|
3294
|
818 |
|
|
819 In this example, we don't check for errors, but that is not difficult. |
|
|
820 All of the Octave's built-in functions do some form of checking on their |
|
|
821 arguments, so you can check the source code for those functions for |
|
|
822 examples of various strategies for verifying that the correct number and |
|
|
823 types of arguments have been supplied. |
|
|
824 |
|
|
825 The next statements |
|
|
826 |
|
|
827 @example |
|
|
828 @group |
|
|
829 dx(0) = 77.27 * (x(1) - x(0)*x(1) + x(0) |
|
|
830 - 8.375e-06*pow (x(0), 2)); |
|
|
831 |
|
|
832 dx(1) = (x(2) - x(0)*x(1) - x(1)) / 77.27; |
|
|
833 |
|
|
834 dx(2) = 0.161*(x(0) - x(2)); |
|
|
835 @end group |
|
|
836 @end example |
|
|
837 |
|
|
838 @noindent |
|
5016
|
839 define the right-hand side of the differential equation. Finally, we |
|
3294
|
840 can return @code{dx}: |
|
|
841 |
|
|
842 @example |
|
|
843 return octave_value (dx); |
|
|
844 @end example |
|
|
845 |
|
|
846 @noindent |
|
|
847 The actual return type is @code{octave_value_list}, but it is only |
|
|
848 necessary to convert the return type to an @code{octave_value} because |
|
|
849 there is a default constructor that can automatically create an object |
|
|
850 of that type from an @code{octave_value} object, so we can just use that |
|
|
851 instead. |
|
|
852 |
|
|
853 To use this file, your version of Octave must support dynamic linking. |
|
|
854 To find out if it does, type the command |
|
|
855 @kbd{octave_config_info ("dld")} at the Octave prompt. Support for |
|
|
856 dynamic linking is included if this command returns 1. |
|
|
857 |
|
|
858 To compile the example file, type the command @samp{mkoctfile |
|
|
859 oregonator.cc} at the shell prompt. The script @code{mkoctfile} should |
|
|
860 have been installed along with Octave. Running it will create a file |
|
|
861 called @file{oregonator.oct} that can be loaded by Octave. To test the |
|
|
862 @file{oregonator.oct} file, start Octave and type the command |
|
|
863 |
|
|
864 @example |
|
|
865 oregonator ([1, 2, 3], 0) |
|
|
866 @end example |
|
|
867 |
|
|
868 @noindent |
|
|
869 at the Octave prompt. Octave should respond by printing |
|
|
870 |
|
|
871 @example |
|
|
872 @group |
|
|
873 ans = |
|
|
874 |
|
|
875 77.269353 |
|
|
876 -0.012942 |
|
|
877 -0.322000 |
|
|
878 @end group |
|
|
879 @end example |
|
|
880 |
|
|
881 You can now use the @file{oregonator.oct} file just as you would the |
|
|
882 @code{oregonator.m} file to solve the set of differential equations. |
|
|
883 |
|
|
884 On a 133 MHz Pentium running Linux, Octave can solve the problem shown |
|
3402
|
885 in @ref{Ordinary Differential Equations}, in about 1.4 seconds using the |
|
3294
|
886 dynamically linked function, compared to about 19 seconds using the |
|
|
887 M-file. Similar decreases in execution time can be expected for other |
|
|
888 functions, particularly those that rely on functions like @code{lsode} |
|
|
889 that require user-supplied functions. |
|
|
890 |
|
3428
|
891 Just as for M-files, Octave will automatically reload a dynamically linked |
|
|
892 function when the file that defines it is more recent than the last |
|
|
893 time that the function was loaded. If more than one function is defined |
|
|
894 in a single @file{.oct} file, reloading the file may force other |
|
|
895 functions to be cleared and reloaded. If all the functions loaded from |
|
|
896 a given @file{.oct} file are cleared, Octave will automatically unload |
|
|
897 the @file{.oct} file. |
|
3294
|
898 |
|
5775
|
899 @c FIXME -- is there a better place for this? |
|
3428
|
900 |
|
|
901 @DOCSTRING(variables_can_hide_functions) |
|
|
902 |
|
3294
|
903 Additional examples for writing dynamically linked functions are |
|
|
904 available in the files in the @file{src} directory of the Octave |
|
|
905 distribution. Currently, this includes the files |
|
|
906 |
|
|
907 @example |
|
|
908 @group |
|
|
909 balance.cc fft2.cc inv.cc qzval.cc |
|
|
910 chol.cc filter.cc log.cc schur.cc |
|
|
911 colloc.cc find.cc lsode.cc sort.cc |
|
|
912 dassl.cc fsolve.cc lu.cc svd.cc |
|
|
913 det.cc givens.cc minmax.cc syl.cc |
|
|
914 eig.cc hess.cc pinv.cc |
|
|
915 expm.cc ifft.cc qr.cc |
|
|
916 fft.cc ifft2.cc quad.cc |
|
|
917 @end group |
|
|
918 @end example |
|
|
919 |
|
|
920 @noindent |
|
|
921 These files use the macro @code{DEFUN_DLD_BUILTIN} instead of |
|
|
922 @code{DEFUN_DLD}. The difference between these two macros is just that |
|
|
923 @code{DEFUN_DLD_BUILTIN} can define a built-in function that is not |
|
|
924 dynamically loaded if the operating system does not support dynamic |
|
|
925 linking. To define your own dynamically linked functions you should use |
|
|
926 @code{DEFUN_DLD}. |
|
|
927 |
|
|
928 There is currently no detailed description of all the functions that you |
|
|
929 can call in a built-in function. For the time being, you will have to |
|
|
930 read the source code for Octave. |
|
|
931 |
|
4933
|
932 @node Function Handles and Inline |
|
|
933 @section Function Handles and Inline |
|
|
934 @cindex handle, function handles |
|
|
935 @cindex inline, inline functions |
|
|
936 |
|
|
937 This is a place holder for the description of function handles and |
|
|
938 inline functions. |
|
|
939 |
|
|
940 @menu |
|
|
941 * Function Handles:: |
|
|
942 * Inline Functions:: |
|
|
943 @end menu |
|
|
944 |
|
|
945 @node Function Handles |
|
|
946 @subsection Function Handles |
|
|
947 |
|
|
948 @DOCSTRING(functions) |
|
|
949 |
|
|
950 @DOCSTRING(func2str) |
|
|
951 |
|
|
952 @DOCSTRING(str2func) |
|
|
953 |
|
|
954 @node Inline Functions |
|
|
955 @subsection Inline Functions |
|
|
956 |
|
|
957 @DOCSTRING(inline) |
|
|
958 |
|
|
959 @DOCSTRING(argnames) |
|
|
960 |
|
|
961 @DOCSTRING(formula) |
|
|
962 |
|
|
963 @DOCSTRING(vectorize) |
|
|
964 |
|
4167
|
965 @node Organization of Functions |
|
3294
|
966 @section Organization of Functions Distributed with Octave |
|
|
967 |
|
|
968 Many of Octave's standard functions are distributed as function files. |
|
|
969 They are loosely organized by topic, in subdirectories of |
|
|
970 @file{@var{octave-home}/lib/octave/@var{version}/m}, to make it easier |
|
|
971 to find them. |
|
|
972 |
|
|
973 The following is a list of all the function file subdirectories, and the |
|
|
974 types of functions you will find there. |
|
|
975 |
|
|
976 @table @file |
|
|
977 @item audio |
|
|
978 Functions for playing and recording sounds. |
|
|
979 |
|
|
980 @item control |
|
|
981 Functions for design and simulation of automatic control systems. |
|
|
982 |
|
|
983 @item elfun |
|
|
984 Elementary functions. |
|
|
985 |
|
|
986 @item general |
|
|
987 Miscellaneous matrix manipulations, like @code{flipud}, @code{rot90}, |
|
|
988 and @code{triu}, as well as other basic functions, like |
|
4029
|
989 @code{ismatrix}, @code{nargchk}, etc. |
|
3294
|
990 |
|
|
991 @item image |
|
|
992 Image processing tools. These functions require the X Window System. |
|
|
993 |
|
|
994 @item io |
|
|
995 Input-ouput functions. |
|
|
996 |
|
|
997 @item linear-algebra |
|
|
998 Functions for linear algebra. |
|
|
999 |
|
|
1000 @item miscellaneous |
|
|
1001 Functions that don't really belong anywhere else. |
|
|
1002 |
|
|
1003 @item plot |
|
|
1004 A set of functions that implement the @sc{Matlab}-like plotting functions. |
|
|
1005 |
|
|
1006 @item polynomial |
|
|
1007 Functions for manipulating polynomials. |
|
|
1008 |
|
|
1009 @item set |
|
|
1010 Functions for creating and manipulating sets of unique values. |
|
|
1011 |
|
|
1012 @item signal |
|
|
1013 Functions for signal processing applications. |
|
|
1014 |
|
|
1015 @item specfun |
|
|
1016 Special functions. |
|
|
1017 |
|
|
1018 @item special-matrix |
|
|
1019 Functions that create special matrix forms. |
|
|
1020 |
|
|
1021 @item startup |
|
|
1022 Octave's system-wide startup file. |
|
|
1023 |
|
|
1024 @item statistics |
|
|
1025 Statistical functions. |
|
|
1026 |
|
|
1027 @item strings |
|
|
1028 Miscellaneous string-handling functions. |
|
|
1029 |
|
|
1030 @item time |
|
|
1031 Functions related to time keeping. |
|
|
1032 @end table |
