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1 @c Copyright (C) 1996, 1997, 2007 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 * Function Handles Inline Functions and Anonymous Functions:: |
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27 * Commands:: |
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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(inputname) |
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228 |
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229 @DOCSTRING(silent_functions) |
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230 |
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231 @node Multiple Return Values |
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232 @section Multiple Return Values |
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233 |
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234 Unlike many other computer languages, Octave allows you to define |
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235 functions that return more than one value. The syntax for defining |
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236 functions that return multiple values is |
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237 |
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238 @example |
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239 function [@var{ret-list}] = @var{name} (@var{arg-list}) |
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240 @var{body} |
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241 endfunction |
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242 @end example |
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243 |
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244 @noindent |
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245 where @var{name}, @var{arg-list}, and @var{body} have the same meaning |
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246 as before, and @var{ret-list} is a comma-separated list of variable |
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247 names that will hold the values returned from the function. The list of |
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248 return values must have at least one element. If @var{ret-list} has |
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249 only one element, this form of the @code{function} statement is |
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250 equivalent to the form described in the previous section. |
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251 |
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252 Here is an example of a function that returns two values, the maximum |
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253 element of a vector and the index of its first occurrence in the vector. |
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254 |
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255 @example |
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256 @group |
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257 function [max, idx] = vmax (v) |
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258 idx = 1; |
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259 max = v (idx); |
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260 for i = 2:length (v) |
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261 if (v (i) > max) |
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262 max = v (i); |
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263 idx = i; |
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264 endif |
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265 endfor |
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266 endfunction |
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267 @end group |
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268 @end example |
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269 |
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270 In this particular case, the two values could have been returned as |
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271 elements of a single array, but that is not always possible or |
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272 convenient. The values to be returned may not have compatible |
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273 dimensions, and it is often desirable to give the individual return |
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274 values distinct names. |
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275 |
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276 In addition to setting @code{nargin} each time a function is called, |
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277 Octave also automatically initializes @code{nargout} to the number of |
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278 values that are expected to be returned. This allows you to write |
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279 functions that behave differently depending on the number of values that |
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280 the user of the function has requested. The implicit assignment to the |
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281 built-in variable @code{ans} does not figure in the count of output |
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282 arguments, so the value of @code{nargout} may be zero. |
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283 |
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284 The @code{svd} and @code{lu} functions are examples of built-in |
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285 functions that behave differently depending on the value of |
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286 @code{nargout}. |
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287 |
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288 It is possible to write functions that only set some return values. For |
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289 example, calling the function |
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290 |
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291 @example |
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292 function [x, y, z] = f () |
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293 x = 1; |
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294 z = 2; |
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295 endfunction |
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296 @end example |
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297 |
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298 @noindent |
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299 as |
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300 |
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301 @example |
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302 [a, b, c] = f () |
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303 @end example |
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304 |
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305 @noindent |
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306 produces: |
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307 |
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308 @example |
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309 a = 1 |
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310 |
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311 b = [](0x0) |
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312 |
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313 c = 2 |
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314 @end example |
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315 |
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316 @noindent |
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317 along with a warning. |
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318 |
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319 @DOCSTRING(nargout) |
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320 |
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321 @DOCSTRING(nargchk) |
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322 |
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323 @node Variable-length Argument Lists |
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324 @section Variable-length Argument Lists |
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325 @cindex variable-length argument lists |
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326 @cindex @code{...} |
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327 Sometimes the number of input arguments is not known when the function |
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328 is defined. As an example think of a function that returns the smallest |
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329 of all its input arguments. For example, |
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330 |
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331 @example |
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332 a = smallest (1, 2, 3); |
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333 b = smallest (1, 2, 3, 4); |
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334 @end example |
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335 |
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336 @noindent |
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337 In this example both @code{a} and @code{b} would be 1. One way to write |
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338 the @code{smallest} function is |
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339 |
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340 @example |
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341 function val = smallest (arg1, arg2, arg3, arg4, arg5) |
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342 @var{body} |
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343 endfunction |
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344 @end example |
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345 |
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346 @noindent |
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347 and then use the value of @code{nargin} to determine which of the input |
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348 arguments should be considered. The problem with this approach is |
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349 that it can only handle a limited number of input arguments. |
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350 |
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351 Octave supports the @code{varargin} keyword for handling a variable |
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352 number of input arguments. Using @code{varargin} the function |
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353 looks like this |
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354 |
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355 @example |
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356 function val = smallest (varargin) |
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357 @var{body} |
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358 endfunction |
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359 @end example |
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360 |
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361 @noindent |
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362 In the function body the input arguments can be accessed through the |
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363 variable @code{varargin}. This variable is a cell array containing |
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364 all the input arguments. @xref{Cell Arrays}, for details on working |
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365 with cell arrays. The @code{smallest} function can now be defined |
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366 like this |
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367 |
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368 @example |
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369 function val = smallest (varargin) |
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370 val = min ([varargin@{:@}]); |
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371 endfunction |
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372 @end example |
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373 |
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374 @noindent |
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375 This implementation handles any number of input arguments, but it's also |
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376 a very simple solution to the problem. |
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377 |
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378 A slightly more complex example of @code{varargin} is a function |
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379 @code{print_arguments} that prints all input arguments. Such a function |
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380 can be defined like this |
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381 |
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382 @example |
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383 function print_arguments (varargin) |
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384 for i = 1:length (varargin) |
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385 printf ("Input argument %d: ", i); |
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386 disp (varargin@{i@}); |
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387 endfor |
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388 endfunction |
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389 @end example |
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390 |
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391 @noindent |
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392 This function produces output like this |
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393 |
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394 @example |
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395 @group |
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396 print_arguments (1, "two", 3); |
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397 @print{} Input argument 1: 1 |
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398 @print{} Input argument 2: two |
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399 @print{} Input argument 3: 3 |
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400 @end group |
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401 @end example |
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402 |
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403 @DOCSTRING(parseparams) |
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404 |
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405 @node Variable-length Return Lists |
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406 @section Variable-length Return Lists |
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407 @cindex variable-length return lists |
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408 It is possible to return a variable number of output arguments from a |
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409 function using a syntax that's similar to the one used with the |
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410 @code{varargin} keyword. To let a function return a variable number of |
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411 output arguments the @code{varargout} keyword is used. As with |
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412 @code{varargin} @code{varargout} is a cell array that will contain the |
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413 requested output arguments. |
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414 |
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415 As an example the following function sets the first output argument to |
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416 1, the second to 2, and so on. |
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417 |
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418 @example |
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419 function varargout = one_to_n () |
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420 for i = 1:nargout |
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421 varargout@{i@} = i; |
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422 endfor |
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423 endfunction |
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424 @end example |
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425 |
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426 @noindent |
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427 When called this function returns values like this |
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428 |
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429 @example |
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430 @group |
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431 [a, b, c] = one_to_n () |
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432 @result{} a = 1 |
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433 @result{} b = 2 |
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434 @result{} c = 3 |
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435 @end group |
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436 @end example |
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437 |
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438 @DOCSTRING(deal) |
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439 |
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440 @node Returning From a Function |
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441 @section Returning From a Function |
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442 |
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443 The body of a user-defined function can contain a @code{return} statement. |
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444 This statement returns control to the rest of the Octave program. It |
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445 looks like this: |
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446 |
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447 @example |
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448 return |
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449 @end example |
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450 |
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451 Unlike the @code{return} statement in C, Octave's @code{return} |
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452 statement cannot be used to return a value from a function. Instead, |
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453 you must assign values to the list of return variables that are part of |
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454 the @code{function} statement. The @code{return} statement simply makes |
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455 it easier to exit a function from a deeply nested loop or conditional |
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456 statement. |
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457 |
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458 Here is an example of a function that checks to see if any elements of a |
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459 vector are nonzero. |
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460 |
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461 @example |
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462 @group |
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463 function retval = any_nonzero (v) |
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464 retval = 0; |
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465 for i = 1:length (v) |
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466 if (v (i) != 0) |
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467 retval = 1; |
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468 return; |
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469 endif |
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470 endfor |
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471 printf ("no nonzero elements found\n"); |
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472 endfunction |
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473 @end group |
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474 @end example |
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475 |
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476 Note that this function could not have been written using the |
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477 @code{break} statement to exit the loop once a nonzero value is found |
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478 without adding extra logic to avoid printing the message if the vector |
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479 does contain a nonzero element. |
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480 |
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481 @deffn {Keyword} return |
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482 When Octave encounters the keyword @code{return} inside a function or |
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483 script, it returns control to the caller immediately. At the top level, |
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484 the return statement is ignored. A @code{return} statement is assumed |
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485 at the end of every function definition. |
|
5763
|
486 @end deffn |
|
3294
|
487 |
|
3371
|
488 @DOCSTRING(return_last_computed_value) |
|
3294
|
489 |
|
6510
|
490 @node Default Arguments |
|
|
491 @section Default Arguments |
|
|
492 @cindex default arguments |
|
|
493 |
|
|
494 Since Octave supports variable number of input arguments, it is very useful |
|
|
495 to assign default values to some input arguments. When an input argument |
|
|
496 is declared in the argument list it is possible to assign a default |
|
|
497 value to the argument like this |
|
|
498 |
|
|
499 @example |
|
|
500 function @var{name} (@var{arg1} = @var{val1}, @dots{}) |
|
|
501 @var{body} |
|
|
502 endfunction |
|
|
503 @end example |
|
|
504 |
|
|
505 @noindent |
|
|
506 If no value is assigned to @var{arg1} by the user, it will have the |
|
|
507 value @var{val1}. |
|
|
508 |
|
|
509 As an example, the following function implements a variant of the classic |
|
|
510 ``Hello, World'' program. |
|
|
511 @example |
|
|
512 function hello (who = "World") |
|
|
513 printf ("Hello, %s!\n", who); |
|
|
514 endfunction |
|
|
515 @end example |
|
|
516 |
|
|
517 @noindent |
|
|
518 When called without an input argument the function prints the following |
|
|
519 @example |
|
|
520 @group |
|
|
521 hello (); |
|
|
522 @print{} Hello, World! |
|
|
523 @end group |
|
|
524 @end example |
|
|
525 |
|
|
526 @noindent |
|
|
527 and when it's called with an input argument it prints the following |
|
|
528 @example |
|
|
529 @group |
|
|
530 hello ("Beautiful World of Free Software"); |
|
|
531 @print{} Hello, Beautiful World of Free Software! |
|
|
532 @end group |
|
|
533 @end example |
|
|
534 |
|
|
535 Sometimes it is useful to explicitly tell Octave to use the default value |
|
|
536 of an input argument. This can be done writing a @samp{:} as the value |
|
|
537 of the input argument when calling the function. |
|
|
538 @example |
|
|
539 @group |
|
|
540 hello (:); |
|
|
541 @print{} Hello, World! |
|
|
542 @end group |
|
|
543 @end example |
|
|
544 |
|
4167
|
545 @node Function Files |
|
3294
|
546 @section Function Files |
|
|
547 @cindex function file |
|
|
548 |
|
|
549 Except for simple one-shot programs, it is not practical to have to |
|
|
550 define all the functions you need each time you need them. Instead, you |
|
|
551 will normally want to save them in a file so that you can easily edit |
|
|
552 them, and save them for use at a later time. |
|
|
553 |
|
|
554 Octave does not require you to load function definitions from files |
|
|
555 before using them. You simply need to put the function definitions in a |
|
|
556 place where Octave can find them. |
|
|
557 |
|
|
558 When Octave encounters an identifier that is undefined, it first looks |
|
|
559 for variables or functions that are already compiled and currently |
|
|
560 listed in its symbol table. If it fails to find a definition there, it |
|
6556
|
561 searches a list of directories (the @dfn{path}) for files ending in |
|
6554
|
562 @file{.m} that have the same base name as the undefined |
|
|
563 identifier.@footnote{The @samp{.m} suffix was chosen for compatibility |
|
|
564 with @sc{Matlab}.} Once Octave finds a file with a name that matches, |
|
|
565 the contents of the file are read. If it defines a @emph{single} |
|
|
566 function, it is compiled and executed. @xref{Script Files}, for more |
|
|
567 information about how you can define more than one function in a single |
|
|
568 file. |
|
3294
|
569 |
|
|
570 When Octave defines a function from a function file, it saves the full |
|
6554
|
571 name of the file it read and the time stamp on the file. If the time |
|
|
572 stamp on the file changes, Octave may reload the file. When Octave is |
|
|
573 running interactively, time stamp checking normally happens at most once |
|
|
574 each time Octave prints the prompt. Searching for new function |
|
|
575 definitions also occurs if the current working directory changes. |
|
3294
|
576 |
|
|
577 Checking the time stamp allows you to edit the definition of a function |
|
|
578 while Octave is running, and automatically use the new function |
|
6554
|
579 definition without having to restart your Octave session. |
|
3294
|
580 |
|
|
581 To avoid degrading performance unnecessarily by checking the time stamps |
|
|
582 on functions that are not likely to change, Octave assumes that function |
|
|
583 files in the directory tree |
|
|
584 @file{@var{octave-home}/share/octave/@var{version}/m} |
|
|
585 will not change, so it doesn't have to check their time stamps every time the |
|
|
586 functions defined in those files are used. This is normally a very good |
|
|
587 assumption and provides a significant improvement in performance for the |
|
|
588 function files that are distributed with Octave. |
|
|
589 |
|
|
590 If you know that your own function files will not change while you are |
|
6554
|
591 running Octave, you can improve performance by calling |
|
|
592 @code{ignore_function_time_stamp ("all")}, so that Octave will |
|
|
593 ignore the time stamps for all function files. Passing |
|
|
594 @code{"system"} to this function resets the default behavior. |
|
3294
|
595 |
|
5775
|
596 @c FIXME -- note about time stamps on files in NFS environments? |
|
3294
|
597 |
|
6549
|
598 @DOCSTRING(mfilename) |
|
|
599 |
|
6638
|
600 @DOCSTRING(ignore_function_time_stamp) |
|
|
601 |
|
|
602 @menu |
|
|
603 * Manipulating the load path:: |
|
|
604 * Subfunctions:: |
|
|
605 * Overloading and Autoloading:: |
|
|
606 * Function Locking:: |
|
|
607 @end menu |
|
|
608 |
|
|
609 @node Manipulating the load path |
|
|
610 @subsection Manipulating the load path |
|
|
611 |
|
|
612 When a function is called Octave searches a list of directories for |
|
|
613 a file that contains the function declaration. This list of directories |
|
|
614 is known as the load path. By default the load path contains |
|
|
615 a list of directories distributed with Octave plus the current |
|
|
616 working directory. To see your current load path call the @code{path} |
|
|
617 function without any input or output arguments. |
|
|
618 |
|
|
619 It is possible to add or remove directories to or from the load path |
|
|
620 using the @code{addpath} and @code{rmpath}. As an example, the following |
|
|
621 code adds @samp{~/Octave} to the load path. |
|
|
622 |
|
|
623 @example |
|
|
624 addpath("~/Octave") |
|
|
625 @end example |
|
|
626 |
|
|
627 @noindent |
|
|
628 After this the directory @samp{~/Octave} will be searched for functions. |
|
|
629 |
|
6502
|
630 @DOCSTRING(addpath) |
|
|
631 |
|
|
632 @DOCSTRING(genpath) |
|
|
633 |
|
|
634 @DOCSTRING(rmpath) |
|
|
635 |
|
|
636 @DOCSTRING(savepath) |
|
|
637 |
|
6477
|
638 @DOCSTRING(path) |
|
3294
|
639 |
|
6502
|
640 @DOCSTRING(pathdef) |
|
|
641 |
|
|
642 @DOCSTRING(pathsep) |
|
|
643 |
|
3428
|
644 @DOCSTRING(rehash) |
|
|
645 |
|
|
646 @DOCSTRING(file_in_loadpath) |
|
|
647 |
|
6556
|
648 @node Subfunctions |
|
|
649 @subsection Subfunctions |
|
|
650 |
|
|
651 A function file may contain secondary functions called |
|
|
652 @dfn{subfunctions}. These secondary functions are only visible to the |
|
|
653 other functions in the same function file. For example, a file |
|
|
654 @file{f.m} containing |
|
|
655 |
|
|
656 @example |
|
|
657 @group |
|
|
658 function f () |
|
|
659 printf ("in f, calling g\n"); |
|
|
660 g () |
|
|
661 endfunction |
|
|
662 function g () |
|
|
663 printf ("in g, calling h\n"); |
|
6638
|
664 h () |
|
6556
|
665 endfunction |
|
|
666 function h () |
|
|
667 printf ("in h\n") |
|
|
668 endfunction |
|
|
669 @end group |
|
|
670 @end example |
|
|
671 |
|
|
672 @noindent |
|
|
673 defines a main function @code{f} and two subfunctions. The |
|
|
674 subfunctions @code{g} and @code{h} may only be called from the main |
|
|
675 function @code{f} or from the other subfunctions, but not from outside |
|
|
676 the file @file{f.m}. |
|
|
677 |
|
6635
|
678 @node Overloading and Autoloading |
|
|
679 @subsection Overloading and Autoloading |
|
|
680 |
|
|
681 The @code{dispatch} function can be used to alias one function name to |
|
|
682 another. It can be used to alias all calls to a particular function name |
|
|
683 to another function, or the alias can be limited to only a particular |
|
|
684 variable type. Consider the example |
|
|
685 |
|
|
686 @example |
|
|
687 @group |
|
|
688 function y = spsin (x) |
|
|
689 printf ("Calling spsin\n"); |
|
|
690 fflush(stdout); |
|
|
691 y = spfun ("sin", x); |
|
|
692 endfunction |
|
|
693 |
|
|
694 dispatch ("sin", "spsin", "sparse matrix"); |
|
|
695 y0 = sin(eye(3)); |
|
|
696 y1 = sin(speye(3)); |
|
|
697 @end group |
|
|
698 @end example |
|
|
699 |
|
|
700 @noindent |
|
|
701 Which aliases the @code{spsin} to @code{sin}, but only for real sparse |
|
|
702 matrices. Note that the builtin @code{sin} already correctly treats |
|
|
703 sparse matrices and so this example is only illustrative. |
|
|
704 |
|
|
705 @DOCSTRING(dispatch) |
|
|
706 |
|
|
707 @DOCSTRING(builtin) |
|
|
708 |
|
|
709 A single dynamically linked file might define several |
|
|
710 functions. However, as Octave searches for functions based on the |
|
|
711 functions filename, Octave needs a manner in which to find each of the |
|
|
712 functions in the dynamically linked file. On operating systems that |
|
|
713 support symbolic links, it is possible to create a symbolic link to the |
|
|
714 original file for each of the functions which it contains. |
|
|
715 |
|
|
716 However, there is at least one well known operating system that doesn't |
|
|
717 support symbolic links. Making copies of the original file for each of |
|
|
718 the functions is also possible, but is undesirable as it multiples the |
|
|
719 amount of disk space used by Octave. Instead Octave supplies the |
|
|
720 @code{autoload} function, that permits the user to define in which |
|
|
721 file a certain function will be found. |
|
|
722 |
|
|
723 @DOCSTRING(autoload) |
|
|
724 |
|
|
725 @node Function Locking |
|
|
726 @subsection Function Locking |
|
|
727 |
|
|
728 It is sometime desirable to lock a function into memory with the |
|
|
729 @code{mlock} function. This is typically used for dynamically linked |
|
6899
|
730 functions in Oct-files or mex-files that contain some initialization, |
|
|
731 and it is desirable that calling @code{clear} does not remove this |
|
6635
|
732 initialization. |
|
|
733 |
|
6899
|
734 As an example, |
|
|
735 |
|
|
736 @example |
|
|
737 mlock ("my_function"); |
|
|
738 @end example |
|
|
739 |
|
|
740 @noindent |
|
|
741 prevents @code{my_function} from being removed from memory, even if |
|
|
742 @code{clear} is called. It is possible to determine if a function is |
|
|
743 locked into memory with the @code{mislocked}, and to unlock a function |
|
|
744 with @code{munlock}, which the following illustrates. |
|
|
745 |
|
|
746 @example |
|
|
747 @group |
|
|
748 mlock ("my_function"); |
|
|
749 mislocked ("my_function") |
|
|
750 @result{} ans = 1 |
|
|
751 munlock ("my_function"); |
|
|
752 mislocked ("my_function") |
|
|
753 @result{} ans = 0 |
|
|
754 @end group |
|
|
755 @end example |
|
|
756 |
|
|
757 A common use of @code{mlock} is to prevent persistent variables from |
|
|
758 being removed from memory, as the following example shows. |
|
|
759 |
|
|
760 @example |
|
|
761 @group |
|
|
762 function count_calls() |
|
|
763 persistent calls = 0; |
|
|
764 printf ("'count_calls' has been called %d times\n", ++calls); |
|
|
765 endfunction |
|
|
766 mlock ("count_calls"); |
|
|
767 |
|
|
768 count_calls (); |
|
|
769 @print{} 'count_calls' has been called 1 times |
|
|
770 |
|
|
771 clear count_calls |
|
|
772 count_calls (); |
|
|
773 @print{} 'count_calls' has been called 2 times |
|
|
774 @end group |
|
|
775 @end example |
|
|
776 |
|
|
777 @noindent |
|
|
778 It is, however, often inconvenient to lock a function from the prompt, |
|
|
779 so it is also possible to lock a function from within its body. This |
|
|
780 is simply done by calling @code{mlock} from within the function. |
|
|
781 |
|
|
782 @example |
|
|
783 @group |
|
|
784 function count_calls () |
|
|
785 mlock (); |
|
|
786 persistent calls = 0; |
|
|
787 printf ("'count_calls' has been called %d times\n", ++calls); |
|
|
788 endfunction |
|
|
789 @end group |
|
|
790 @end example |
|
|
791 |
|
|
792 @code{mlock} might equally be used to prevent changes to a function from having |
|
6635
|
793 effect in Octave, though a similar effect can be had with the |
|
|
794 @code{ignore_function_time_stamp} function. |
|
|
795 |
|
|
796 @DOCSTRING(mlock) |
|
|
797 |
|
|
798 @DOCSTRING(munlock) |
|
|
799 |
|
|
800 @DOCSTRING(mislocked) |
|
|
801 |
|
4167
|
802 @node Script Files |
|
3294
|
803 @section Script Files |
|
|
804 |
|
|
805 A script file is a file containing (almost) any sequence of Octave |
|
|
806 commands. It is read and evaluated just as if you had typed each |
|
|
807 command at the Octave prompt, and provides a convenient way to perform a |
|
|
808 sequence of commands that do not logically belong inside a function. |
|
|
809 |
|
|
810 Unlike a function file, a script file must @emph{not} begin with the |
|
|
811 keyword @code{function}. If it does, Octave will assume that it is a |
|
|
812 function file, and that it defines a single function that should be |
|
|
813 evaluated as soon as it is defined. |
|
|
814 |
|
|
815 A script file also differs from a function file in that the variables |
|
|
816 named in a script file are not local variables, but are in the same |
|
|
817 scope as the other variables that are visible on the command line. |
|
|
818 |
|
|
819 Even though a script file may not begin with the @code{function} |
|
|
820 keyword, it is possible to define more than one function in a single |
|
|
821 script file and load (but not execute) all of them at once. To do |
|
|
822 this, the first token in the file (ignoring comments and other white |
|
|
823 space) must be something other than @code{function}. If you have no |
|
|
824 other statements to evaluate, you can use a statement that has no |
|
|
825 effect, like this: |
|
|
826 |
|
|
827 @example |
|
|
828 @group |
|
|
829 # Prevent Octave from thinking that this |
|
|
830 # is a function file: |
|
|
831 |
|
|
832 1; |
|
|
833 |
|
|
834 # Define function one: |
|
|
835 |
|
|
836 function one () |
|
|
837 ... |
|
|
838 @end group |
|
|
839 @end example |
|
|
840 |
|
|
841 To have Octave read and compile these functions into an internal form, |
|
6638
|
842 you need to make sure that the file is in Octave's load path |
|
6477
|
843 (accessible through the @code{path} function), then simply type the |
|
|
844 base name of the file that contains the commands. (Octave uses the |
|
|
845 same rules to search for script files as it does to search for |
|
|
846 function files.) |
|
3294
|
847 |
|
|
848 If the first token in a file (ignoring comments) is @code{function}, |
|
|
849 Octave will compile the function and try to execute it, printing a |
|
|
850 message warning about any non-whitespace characters that appear after |
|
|
851 the function definition. |
|
|
852 |
|
|
853 Note that Octave does not try to look up the definition of any identifier |
|
|
854 until it needs to evaluate it. This means that Octave will compile the |
|
|
855 following statements if they appear in a script file, or are typed at |
|
|
856 the command line, |
|
|
857 |
|
|
858 @example |
|
|
859 @group |
|
|
860 # not a function file: |
|
|
861 1; |
|
|
862 function foo () |
|
|
863 do_something (); |
|
|
864 endfunction |
|
|
865 function do_something () |
|
|
866 do_something_else (); |
|
|
867 endfunction |
|
|
868 @end group |
|
|
869 @end example |
|
|
870 |
|
|
871 @noindent |
|
|
872 even though the function @code{do_something} is not defined before it is |
|
|
873 referenced in the function @code{foo}. This is not an error because |
|
|
874 Octave does not need to resolve all symbols that are referenced by a |
|
|
875 function until the function is actually evaluated. |
|
|
876 |
|
|
877 Since Octave doesn't look for definitions until they are needed, the |
|
|
878 following code will always print @samp{bar = 3} whether it is typed |
|
|
879 directly on the command line, read from a script file, or is part of a |
|
|
880 function body, even if there is a function or script file called |
|
6477
|
881 @file{bar.m} in Octave's path. |
|
3294
|
882 |
|
|
883 @example |
|
|
884 @group |
|
|
885 eval ("bar = 3"); |
|
|
886 bar |
|
|
887 @end group |
|
|
888 @end example |
|
|
889 |
|
|
890 Code like this appearing within a function body could fool Octave if |
|
|
891 definitions were resolved as the function was being compiled. It would |
|
|
892 be virtually impossible to make Octave clever enough to evaluate this |
|
|
893 code in a consistent fashion. The parser would have to be able to |
|
|
894 perform the call to @code{eval} at compile time, and that would be |
|
|
895 impossible unless all the references in the string to be evaluated could |
|
|
896 also be resolved, and requiring that would be too restrictive (the |
|
|
897 string might come from user input, or depend on things that are not |
|
|
898 known until the function is evaluated). |
|
|
899 |
|
|
900 Although Octave normally executes commands from script files that have |
|
|
901 the name @file{@var{file}.m}, you can use the function @code{source} to |
|
|
902 execute commands from any file. |
|
|
903 |
|
3371
|
904 @DOCSTRING(source) |
|
3294
|
905 |
|
6638
|
906 @node Function Handles Inline Functions and Anonymous Functions |
|
|
907 @section Function Handles, Inline Functions, and Anonymous Functions |
|
4933
|
908 @cindex handle, function handles |
|
|
909 @cindex inline, inline functions |
|
6638
|
910 @cindex anonymous functions |
|
4933
|
911 |
|
6638
|
912 It can be very convenient store a function in a variable so that it |
|
|
913 can be passed to a different function. For example, a function that |
|
|
914 performs numerical minimisation needs access to the function that |
|
|
915 should be minimised. |
|
4933
|
916 |
|
|
917 @menu |
|
|
918 * Function Handles:: |
|
6554
|
919 * Anonymous Functions:: |
|
4933
|
920 * Inline Functions:: |
|
|
921 @end menu |
|
|
922 |
|
|
923 @node Function Handles |
|
|
924 @subsection Function Handles |
|
|
925 |
|
6554
|
926 A function handle is a pointer to another function and is defined with |
|
|
927 the syntax |
|
|
928 |
|
|
929 @example |
|
|
930 @@@var{function-name} |
|
|
931 @end example |
|
|
932 |
|
|
933 @noindent |
|
|
934 For example |
|
|
935 |
|
|
936 @example |
|
6556
|
937 f = @@sin; |
|
6554
|
938 @end example |
|
|
939 |
|
|
940 @noindent |
|
6570
|
941 Creates a function handle called @code{f} that refers to the |
|
6554
|
942 function @code{sin}. |
|
|
943 |
|
|
944 Function handles are used to call other functions indirectly, or to pass |
|
|
945 a function as an argument to another function like @code{quad} or |
|
|
946 @code{fsolve}. For example |
|
|
947 |
|
|
948 @example |
|
6556
|
949 f = @@sin; |
|
6554
|
950 quad (f, 0, pi) |
|
6929
|
951 @result{} 2 |
|
6554
|
952 @end example |
|
|
953 |
|
|
954 You may use @code{feval} to call a function using function handle, or |
|
6570
|
955 simply write the name of the function handle followed by an argument |
|
6554
|
956 list. If there are no arguments, you must use an empty argument list |
|
|
957 @samp{()}. For example |
|
|
958 |
|
|
959 @example |
|
6556
|
960 f = @@sin; |
|
6554
|
961 feval (f, pi/4) |
|
6570
|
962 @result{} 0.70711 |
|
6554
|
963 f (pi/4) |
|
6570
|
964 @result{} 0.70711 |
|
6554
|
965 @end example |
|
|
966 |
|
4933
|
967 @DOCSTRING(functions) |
|
|
968 |
|
|
969 @DOCSTRING(func2str) |
|
|
970 |
|
|
971 @DOCSTRING(str2func) |
|
|
972 |
|
6570
|
973 @node Anonymous Functions |
|
6554
|
974 @subsection Anonymous Functions |
|
|
975 |
|
|
976 Anonymous functions are defined using the syntax |
|
|
977 |
|
|
978 @example |
|
|
979 @@(@var{argument-list}) @var{expression} |
|
|
980 @end example |
|
|
981 |
|
|
982 @noindent |
|
|
983 Any variables that are not found in the argument list are inherited from |
|
|
984 the enclosing scope. Anonymous functions are useful for creating simple |
|
|
985 unnamed functions from expressions or for wrapping calls to other |
|
|
986 functions to adapt them for use by functions like @code{quad}. For |
|
|
987 example, |
|
|
988 |
|
|
989 @example |
|
|
990 f = @@(x) x.^2; |
|
|
991 quad (f, 0, 10) |
|
6570
|
992 @result{} 333.33 |
|
6554
|
993 @end example |
|
|
994 |
|
|
995 @noindent |
|
|
996 creates a simple unnamed function from the expression @code{x.^2} and |
|
|
997 passes it to @code{quad}, |
|
|
998 |
|
|
999 @example |
|
|
1000 quad (@@(x) sin (x), 0, pi) |
|
6933
|
1001 @result{} 2 |
|
6554
|
1002 @end example |
|
|
1003 |
|
|
1004 @noindent |
|
|
1005 wraps another function, and |
|
|
1006 |
|
|
1007 @example |
|
|
1008 a = 1; |
|
|
1009 b = 2; |
|
|
1010 quad (@@(x) betainc (x, a, b), 0, 0.4) |
|
6929
|
1011 @result{} 0.13867 |
|
6554
|
1012 @end example |
|
|
1013 |
|
|
1014 @noindent |
|
|
1015 adapts a function with several parameters to the form required by |
|
|
1016 @code{quad}. In this example, the values of @var{a} and @var{b} that |
|
|
1017 are passed to @code{betainc} are inherited from the current |
|
|
1018 environment. |
|
|
1019 |
|
4933
|
1020 @node Inline Functions |
|
|
1021 @subsection Inline Functions |
|
|
1022 |
|
6638
|
1023 An inline function is created from a string containing the function |
|
|
1024 body using the @code{inline} function. The following code defines the |
|
|
1025 function @math{f(x) = x^2 + 2}. |
|
|
1026 |
|
|
1027 @example |
|
|
1028 f = inline("x^2 + 2"); |
|
|
1029 @end example |
|
|
1030 |
|
|
1031 @noindent |
|
|
1032 After this it is possible to evaluate @math{f} at any @math{x} by |
|
|
1033 writing @code{f(x)}. |
|
|
1034 |
|
4933
|
1035 @DOCSTRING(inline) |
|
|
1036 |
|
|
1037 @DOCSTRING(argnames) |
|
|
1038 |
|
|
1039 @DOCSTRING(formula) |
|
|
1040 |
|
|
1041 @DOCSTRING(vectorize) |
|
|
1042 |
|
6549
|
1043 @node Commands |
|
|
1044 @section Commands |
|
|
1045 |
|
6638
|
1046 Commands are a special class of functions that only accept string |
|
|
1047 input arguments. A command can be called as an ordinary function, but |
|
|
1048 it can also be called without the parentheses like the following example |
|
|
1049 shows |
|
|
1050 |
|
|
1051 @example |
|
|
1052 my_command hello world |
|
|
1053 @end example |
|
|
1054 |
|
|
1055 @noindent |
|
|
1056 which is the same as |
|
|
1057 |
|
|
1058 @example |
|
|
1059 my_command("hello", "world") |
|
|
1060 @end example |
|
|
1061 |
|
|
1062 The general form of a command call is |
|
|
1063 |
|
|
1064 @example |
|
|
1065 @var{name} @var{arg1} @var{arg2} @dots{} |
|
|
1066 @end example |
|
|
1067 |
|
|
1068 @noindent |
|
|
1069 which translates directly to |
|
|
1070 |
|
|
1071 @example |
|
|
1072 @var{name} ("@var{arg1}", "@var{arg2}", @dots{}) |
|
|
1073 @end example |
|
|
1074 |
|
7001
|
1075 A function can be used as a command if it accepts string input arguments. |
|
6638
|
1076 To do this, the function must be marked as a command, which can be done |
|
|
1077 with the @code{mark_as_command} command like this |
|
|
1078 |
|
|
1079 @example |
|
|
1080 mark_as_command name |
|
|
1081 @end example |
|
|
1082 |
|
|
1083 @noindent |
|
|
1084 where @code{name} is the function to be marked as a command. |
|
|
1085 |
|
|
1086 One difficulty of commands occurs when one of the string input arguments |
|
|
1087 are stored in a variable. Since Octave can't tell the difference between |
|
|
1088 a variable name, and an ordinary string, it is not possible to pass a |
|
|
1089 variable as input to a command. In such a situation a command must be |
|
|
1090 called as a function. |
|
|
1091 |
|
6549
|
1092 @DOCSTRING(mark_as_command) |
|
|
1093 |
|
|
1094 @DOCSTRING(unmark_command) |
|
|
1095 |
|
|
1096 @DOCSTRING(iscommand) |
|
|
1097 |
|
|
1098 @DOCSTRING(mark_as_rawcommand) |
|
|
1099 |
|
|
1100 @DOCSTRING(unmark_rawcommand) |
|
|
1101 |
|
|
1102 @DOCSTRING(israwcommand) |
|
|
1103 |
|
4167
|
1104 @node Organization of Functions |
|
3294
|
1105 @section Organization of Functions Distributed with Octave |
|
|
1106 |
|
|
1107 Many of Octave's standard functions are distributed as function files. |
|
|
1108 They are loosely organized by topic, in subdirectories of |
|
|
1109 @file{@var{octave-home}/lib/octave/@var{version}/m}, to make it easier |
|
|
1110 to find them. |
|
|
1111 |
|
|
1112 The following is a list of all the function file subdirectories, and the |
|
|
1113 types of functions you will find there. |
|
|
1114 |
|
|
1115 @table @file |
|
|
1116 @item audio |
|
|
1117 Functions for playing and recording sounds. |
|
|
1118 |
|
|
1119 @item control |
|
|
1120 Functions for design and simulation of automatic control systems. |
|
|
1121 |
|
|
1122 @item elfun |
|
|
1123 Elementary functions. |
|
|
1124 |
|
6554
|
1125 @item finance |
|
|
1126 Functions for computing interest payments, investment values, and rates |
|
|
1127 of return. |
|
|
1128 |
|
3294
|
1129 @item general |
|
|
1130 Miscellaneous matrix manipulations, like @code{flipud}, @code{rot90}, |
|
|
1131 and @code{triu}, as well as other basic functions, like |
|
4029
|
1132 @code{ismatrix}, @code{nargchk}, etc. |
|
3294
|
1133 |
|
|
1134 @item image |
|
|
1135 Image processing tools. These functions require the X Window System. |
|
|
1136 |
|
|
1137 @item io |
|
|
1138 Input-ouput functions. |
|
|
1139 |
|
|
1140 @item linear-algebra |
|
|
1141 Functions for linear algebra. |
|
|
1142 |
|
|
1143 @item miscellaneous |
|
|
1144 Functions that don't really belong anywhere else. |
|
|
1145 |
|
6554
|
1146 @item optimization |
|
|
1147 Minimization of functions. |
|
|
1148 |
|
|
1149 @item path |
|
|
1150 Functions to manage the directory path Octave uses to find functions. |
|
|
1151 |
|
|
1152 @item pkg |
|
|
1153 Install external packages of functions in Octave. |
|
|
1154 |
|
3294
|
1155 @item plot |
|
6556
|
1156 Functions for displaying and printing two- and three-dimensional graphs. |
|
3294
|
1157 |
|
|
1158 @item polynomial |
|
|
1159 Functions for manipulating polynomials. |
|
|
1160 |
|
|
1161 @item set |
|
|
1162 Functions for creating and manipulating sets of unique values. |
|
|
1163 |
|
|
1164 @item signal |
|
|
1165 Functions for signal processing applications. |
|
|
1166 |
|
6554
|
1167 @item sparse |
|
|
1168 Functions for handling sparse matrices. |
|
|
1169 |
|
3294
|
1170 @item specfun |
|
|
1171 Special functions. |
|
|
1172 |
|
|
1173 @item special-matrix |
|
|
1174 Functions that create special matrix forms. |
|
|
1175 |
|
|
1176 @item startup |
|
|
1177 Octave's system-wide startup file. |
|
|
1178 |
|
|
1179 @item statistics |
|
|
1180 Statistical functions. |
|
|
1181 |
|
|
1182 @item strings |
|
|
1183 Miscellaneous string-handling functions. |
|
|
1184 |
|
6554
|
1185 @item testfun |
|
|
1186 Perform unit tests on other functions. |
|
|
1187 |
|
3294
|
1188 @item time |
|
|
1189 Functions related to time keeping. |
|
|
1190 @end table |
