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<h3 class="section">4.6 Logical Values</h3>
<p>Octave has built-in support for logical values, i.e., variables that
are either <code>true</code> or <code>false</code>. When comparing two variables,
the result will be a logical value whose value depends on whether or
not the comparison is true.
<p>The basic logical operations are <code>&</code>, <code>|</code>, and <code>!</code>,
which correspond to “Logical And”, “Logical Or”, and “Logical
Negation”. These operations all follow the usual rules of logic.
<p>It is also possible to use logical values as part of standard numerical
calculations. In this case <code>true</code> is converted to <code>1</code>, and
<code>false</code> to 0, both represented using double precision floating
point numbers. So, the result of <code>true*22 - false/6</code> is <code>22</code>.
<p>Logical values can also be used to index matrices and cell arrays.
When indexing with a logical array the result will be a vector containing
the values corresponding to <code>true</code> parts of the logical array.
The following example illustrates this.
<pre class="example"> data = [ 1, 2; 3, 4 ];
idx = (data <= 2);
data(idx)
⇒ ans = [ 1; 2 ]
</pre>
<p class="noindent">Instead of creating the <code>idx</code> array it is possible to replace
<code>data(idx)</code> with <code>data( data <= 2 )</code><!-- /@w --> in the above code.
<p>Logical values can also be constructed by
casting numeric objects to logical values, or by using the <code>true</code>
or <code>false</code> functions.
<!-- logical src/ov-bool-mat.cc -->
<p><a name="doc_002dlogical"></a>
<div class="defun">
— Built-in Function: <b>logical</b> (<var>x</var>)<var><a name="index-logical-295"></a></var><br>
<blockquote><p>Convert <var>x</var> to logical type.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddouble.html#doc_002ddouble">double</a>, <a href="doc_002dsingle.html#doc_002dsingle">single</a>, <a href="doc_002dchar.html#doc_002dchar">char</a>.
</p></blockquote></div>
<!-- true src/data.cc -->
<p><a name="doc_002dtrue"></a>
<div class="defun">
— Built-in Function: <b>true</b> (<var>x</var>)<var><a name="index-true-296"></a></var><br>
— Built-in Function: <b>true</b> (<var>n, m</var>)<var><a name="index-true-297"></a></var><br>
— Built-in Function: <b>true</b> (<var>n, m, k, <small class="dots">...</small></var>)<var><a name="index-true-298"></a></var><br>
<blockquote><p>Return a matrix or N-dimensional array whose elements are all logical 1.
If invoked with a single scalar integer argument, return a square
matrix of the specified size. If invoked with two or more scalar
integer arguments, or a vector of integer values, return an array with
given dimensions.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dfalse.html#doc_002dfalse">false</a>.
</p></blockquote></div>
<!-- false src/data.cc -->
<p><a name="doc_002dfalse"></a>
<div class="defun">
— Built-in Function: <b>false</b> (<var>x</var>)<var><a name="index-false-299"></a></var><br>
— Built-in Function: <b>false</b> (<var>n, m</var>)<var><a name="index-false-300"></a></var><br>
— Built-in Function: <b>false</b> (<var>n, m, k, <small class="dots">...</small></var>)<var><a name="index-false-301"></a></var><br>
<blockquote><p>Return a matrix or N-dimensional array whose elements are all logical 0.
If invoked with a single scalar integer argument, return a square
matrix of the specified size. If invoked with two or more scalar
integer arguments, or a vector of integer values, return an array with
given dimensions.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dtrue.html#doc_002dtrue">true</a>.
</p></blockquote></div>
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