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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 Data Types |
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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, |
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11 a data structure type, and an array that can contain all data types. |
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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 @DOCSTRING(typeinfo) |
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22 |
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23 @menu |
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24 * Built-in Data Types:: |
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25 * User-defined Data Types:: |
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26 * Object Sizes:: |
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27 @end menu |
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28 |
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29 @node Built-in Data Types |
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30 @section Built-in Data Types |
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31 @cindex data types, built-in |
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32 @cindex built-in data types |
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33 |
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34 The standard built-in data types are real and complex scalars and |
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35 matrices, ranges, character strings, a data structure type, and cell |
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36 arrays. Additional built-in data types may be added in future versions. |
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37 If you need a specialized data type that is not currently provided as a |
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38 built-in type, you are encouraged to write your own user-defined data |
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39 type and contribute it for distribution in a future release of Octave. |
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40 |
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41 The data type of a variable can be determined and changed through the |
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42 use of the following functions. |
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43 |
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44 @DOCSTRING(class) |
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45 |
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46 @DOCSTRING(isa) |
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47 |
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48 @DOCSTRING(cast) |
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49 |
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50 @DOCSTRING(typecast) |
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51 |
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52 @DOCSTRING(swapbytes) |
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53 |
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54 @menu |
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55 * Numeric Objects:: |
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56 * Missing Data:: |
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57 * String Objects:: |
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58 * Data Structure Objects:: |
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59 * Cell Array Objects:: |
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60 @end menu |
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61 |
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62 @node Numeric Objects |
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63 @subsection Numeric Objects |
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64 @cindex numeric constant |
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65 @cindex numeric value |
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66 |
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67 Octave's built-in numeric objects include real, complex, and integer |
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68 scalars and matrices. All built-in floating point numeric data is |
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69 currently stored as double precision numbers. On systems that use the |
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70 IEEE floating point format, values in the range of approximately |
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71 @iftex |
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72 @tex |
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73 $2.2251\times10^{-308}$ to $1.7977\times10^{308}$ |
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74 @end tex |
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75 @end iftex |
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76 @ifnottex |
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77 2.2251e-308 to 1.7977e+308 |
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78 @end ifnottex |
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79 can be stored, and the relative precision is approximately |
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80 @iftex |
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81 @tex |
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82 $2.2204\times10^{-16}$. |
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83 @end tex |
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84 @end iftex |
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85 @ifnottex |
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86 2.2204e-16. |
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87 @end ifnottex |
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88 The exact values are given by the variables @code{realmin}, |
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89 @code{realmax}, and @code{eps}, respectively. |
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90 |
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91 Matrix objects can be of any size, and can be dynamically reshaped and |
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92 resized. It is easy to extract individual rows, columns, or submatrices |
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93 using a variety of powerful indexing features. @xref{Index Expressions}. |
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94 |
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95 @xref{Numeric Data Types}, for more information. |
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96 |
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97 @node Missing Data |
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98 @subsection Missing Data |
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99 @cindex missing data |
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100 |
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101 It is possible to represent missing data explicitly in Octave using |
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102 @code{NA} (short for ``Not Available''). Missing data can only be |
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103 represented when data is represented as floating point numbers. In this |
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104 case missing data is represented as a special case of the representation |
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105 of @code{NaN}. |
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106 |
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107 @DOCSTRING(NA) |
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108 |
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109 @DOCSTRING(isna) |
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110 |
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111 @node String Objects |
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112 @subsection String Objects |
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113 @cindex strings |
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114 @cindex character strings |
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115 @opindex " |
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116 @opindex ' |
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117 |
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118 A character string in Octave consists of a sequence of characters |
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119 enclosed in either double-quote or single-quote marks. Internally, |
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120 Octave currently stores strings as matrices of characters. All the |
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121 indexing operations that work for matrix objects also work for strings. |
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122 |
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123 @xref{Strings}, for more information. |
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124 |
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125 @node Data Structure Objects |
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126 @subsection Data Structure Objects |
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127 @cindex structures |
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128 @cindex data structures |
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129 |
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130 Octave's data structure type can help you to organize related objects of |
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131 different types. The current implementation uses an associative array |
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132 with indices limited to strings, but the syntax is more like C-style |
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133 structures. |
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134 |
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135 @xref{Data Structures}, for more information. |
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136 |
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137 @node Cell Array Objects |
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138 @subsection Cell Array Objects |
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139 @cindex cell arrays |
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140 |
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141 A Cell Array in Octave is general array that can hold any number of |
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142 different data types. |
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143 |
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144 @xref{Cell Arrays}, for more information. |
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145 |
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146 @node User-defined Data Types |
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147 @section User-defined Data Types |
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148 @cindex user-defined data types |
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149 @cindex data types, user-defined |
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150 |
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151 Someday I hope to expand this to include a complete description of |
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152 Octave's mechanism for managing user-defined data types. Until this |
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153 feature is documented here, you will have to make do by reading the code |
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154 in the @file{ov.h}, @file{ops.h}, and related files from Octave's |
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155 @file{src} directory. |
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156 |
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157 @node Object Sizes |
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158 @section Object Sizes |
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159 |
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160 The following functions allow you to determine the size of a variable or |
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161 expression. These functions are defined for all objects. They return |
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162 @minus{}1 when the operation doesn't make sense. For example, Octave's |
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163 data structure type doesn't have rows or columns, so the @code{rows} and |
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164 @code{columns} functions return @minus{}1 for structure arguments. |
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165 |
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166 @DOCSTRING(ndims) |
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167 |
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168 @DOCSTRING(columns) |
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169 |
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170 @DOCSTRING(rows) |
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171 |
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172 @DOCSTRING(numel) |
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173 |
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174 @DOCSTRING(length) |
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175 |
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176 @DOCSTRING(size) |
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177 |
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178 @DOCSTRING(isempty) |
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179 |
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180 @DOCSTRING(sizeof) |
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181 |
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182 @DOCSTRING(size_equal) |
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183 |
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184 @DOCSTRING(squeeze) |
