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