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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 Data Types, Numeric Data Types, Getting Started, Top |
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6 @chapter Data Types |
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7 @cindex data types |
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8 |
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9 All versions of Octave include a number of built-in data types, |
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10 including real and complex scalars and matrices, character strings, and |
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11 a data structure type. |
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12 |
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13 It is also possible to define new specialized data types by writing a |
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14 small amount of C++ code. On some systems, new data types can be loaded |
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15 dynamically while Octave is running, so it is not necessary to recompile |
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16 all of Octave just to add a new type. @xref{Dynamically Linked |
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17 Functions} for more information about Octave's dynamic linking |
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18 capabilities. @ref{User-defined Data Types} describes what you must do |
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19 to define a new data type for Octave. |
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20 |
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21 @menu |
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22 * Built-in Data Types:: |
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23 * User-defined Data Types:: |
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24 * Object Sizes:: |
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25 @end menu |
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26 |
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27 @node Built-in Data Types, User-defined Data Types, Data Types, Data Types |
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28 @section Built-in Data Types |
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29 @cindex data types, built-in |
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30 @cindex built-in data types |
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31 |
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32 The standard built-in data types are real and complex scalars and |
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33 matrices, ranges, character strings, and a data structure type. |
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34 Additional built-in data types may be added in future versions. If you |
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35 need a specialized data type that is not currently provided as a |
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36 built-in type, you are encouraged to write your own user-defined data |
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37 type and contribute it for distribution in a future release of Octave. |
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38 |
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39 @menu |
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40 * Numeric Objects:: |
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41 * String Objects:: |
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42 * Data Structure Objects:: |
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43 @end menu |
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44 |
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45 @node Numeric Objects, String Objects, Built-in Data Types, Built-in Data Types |
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46 @subsection Numeric Objects |
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47 @cindex numeric constant |
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48 @cindex numeric value |
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49 |
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50 Octave's built-in numeric objects include real and complex scalars and |
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51 matrices. All built-in numeric data is currently stored as double |
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52 precision numbers. On systems that use the IEEE floating point format, |
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53 values in the range of approximately |
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54 @iftex |
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55 @tex |
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56 $2.2251\times10^{-308}$ to $1.7977\times10^{308}$ |
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57 @end tex |
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58 @end iftex |
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59 @ifinfo |
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60 2.2251e-308 to 1.7977e+308 |
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61 @end ifinfo |
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62 can be stored, and the relative precision is approximately |
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63 @iftex |
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64 @tex |
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65 $2.2204\times10^{-16}$. |
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66 @end tex |
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67 @end iftex |
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68 @ifinfo |
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69 2.2204e-16. |
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70 @end ifinfo |
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71 The exact values are given by the variables @code{realmin}, |
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72 @code{realmax}, and @code{eps}, respectively. |
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73 |
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74 Matrix objects can be of any size, and can be dynamically reshaped and |
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75 resized. It is easy to extract individual rows, columns, or submatrices |
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76 is using a variety of powerful indexing features. @xref{Index Expressions}. |
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77 |
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78 @xref{Numeric Data Types}, for more information. |
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79 |
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80 @node String Objects, Data Structure Objects, Numeric Objects, Built-in Data Types |
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81 @subsection String Objects |
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82 @cindex strings |
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83 @cindex character strings |
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84 @opindex " |
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85 @opindex ' |
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86 |
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87 A character string in Octave consists of a sequence of characters |
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88 enclosed in either double-quote or single-quote marks. Internally, |
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89 Octave currently stores strings as matrices of characters. All the |
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90 indexing operations that work for matrix objects also work for strings. |
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91 |
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92 @xref{Strings}, for more information. |
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93 |
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94 @node Data Structure Objects, , String Objects, Built-in Data Types |
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95 @subsection Data Structure Objects |
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96 @cindex structures |
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97 @cindex data structures |
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98 |
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99 Octave's data structure type can help you to organize related objects of |
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100 different types. The current implementation uses an associative array |
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101 with indices limited to strings, but the syntax is more like C-style |
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102 structures. |
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103 |
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104 @xref{Data Structures}, for more information. |
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105 |
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106 @node User-defined Data Types, Object Sizes, Built-in Data Types, Data Types |
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107 @section User-defined Data Types |
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108 @cindex user-defined data types |
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109 @cindex data types, user-defined |
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110 |
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111 Someday I hope to expand this to include a complete description of |
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112 Octave's mechanism for managing user-defined data types. Until this |
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113 feature is documented here, you will have to make do by reading the code |
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114 in the @file{ov.h}, @file{ops.h}, and related files from Octave's |
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115 @file{src} directory. |
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116 |
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117 @node Object Sizes, , User-defined Data Types, Data Types |
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118 @section Object Sizes |
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119 |
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120 The following functions allow you to determine the size of a variable or |
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121 expression. These functions are defined for all objects. They return |
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122 @minus{}1 when the operation doesn't make sense. For example, Octave's |
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123 data structure type doesn't have rows or columns, so the @code{rows} and |
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124 @code{columns} functions return @minus{}1 for structure arguments. |
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125 |
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126 @deftypefn {Function File} {} columns (@var{a}) |
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127 Return the number of columns of @var{a}. |
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128 @end deftypefn |
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129 |
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130 @deftypefn {Function File} {} rows (@var{a}) |
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131 Return the number of rows of @var{a}. |
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132 @end deftypefn |
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133 |
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134 @deftypefn {Function File} {} length (@var{a}) |
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135 Return the number of rows of @var{a} or the number of columns of |
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136 @var{a}, whichever is larger. |
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137 @end deftypefn |
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138 |
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139 @deftypefn {Function File} {} size (@var{a}, @var{n}) |
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140 Return the number rows and columns of @var{a}. |
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141 |
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142 With one input argument and one output argument, the result is returned |
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143 in a 2 element row vector. If there are two output arguments, the |
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144 number of rows is assigned to the first, and the number of columns to |
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145 the second. For example, |
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146 |
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147 @example |
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148 @group |
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149 size ([1, 2; 3, 4; 5, 6]) |
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150 @result{} [ 3, 2 ] |
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151 |
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152 [nr, nc] = size ([1, 2; 3, 4; 5, 6]) |
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153 @result{} nr = 3 |
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154 @result{} nc = 2 |
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155 @end group |
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156 @end example |
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157 |
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158 If given a second argument of either 1 or 2, @code{size} will return |
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159 only the row or column dimension. For example |
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160 |
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161 @example |
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162 size ([1, 2; 3, 4; 5, 6], 2) |
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163 @result{} 2 |
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164 @end example |
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165 |
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166 @noindent |
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167 returns the number of columns in the given matrix. |
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168 @end deftypefn |
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169 |
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170 @deftypefn {Function File} {} isempty (@var{a}) |
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171 Return 1 if @var{a} is an empty matrix (either the number of rows, or |
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172 the number of columns, or both are zero). Otherwise, return 0. |
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173 @end deftypefn |
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174 |
