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<p>
Previous: <a rel="previous" accesskey="p" href="Promotion-and-Demotion-of-Data-Types.html#Promotion-and-Demotion-of-Data-Types">Promotion and Demotion of Data Types</a>,
Up: <a rel="up" accesskey="u" href="Numeric-Data-Types.html#Numeric-Data-Types">Numeric Data Types</a>
<hr>
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<h3 class="section">4.8 Predicates for Numeric Objects</h3>
<p>Since the type of a variable may change during the execution of a
program, it can be necessary to do type checking at run-time. Doing this
also allows you to change the behavior of a function depending on the
type of the input. As an example, this naive implementation of <code>abs</code>
returns the absolute value of the input if it is a real number, and the
length of the input if it is a complex number.
<pre class="example"> function a = abs (x)
if (isreal (x))
a = sign (x) .* x;
elseif (iscomplex (x))
a = sqrt (real(x).^2 + imag(x).^2);
endif
endfunction
</pre>
<p>The following functions are available for determining the type of a
variable.
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<p><a name="doc_002disnumeric"></a>
<div class="defun">
— Built-in Function: <b>isnumeric</b> (<var>x</var>)<var><a name="index-isnumeric-267"></a></var><br>
<blockquote><p>Return nonzero if <var>x</var> is a numeric object.
</p></blockquote></div>
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<p><a name="doc_002disreal"></a>
<div class="defun">
— Built-in Function: <b>isreal</b> (<var>x</var>)<var><a name="index-isreal-268"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a real-valued numeric object.
</p></blockquote></div>
<!-- data.cc -->
<p><a name="doc_002disfloat"></a>
<div class="defun">
— Built-in Function: <b>isfloat</b> (<var>x</var>)<var><a name="index-isfloat-269"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a floating-point numeric object.
</p></blockquote></div>
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<p><a name="doc_002discomplex"></a>
<div class="defun">
— Built-in Function: <b>iscomplex</b> (<var>x</var>)<var><a name="index-iscomplex-270"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a complex-valued numeric object.
</p></blockquote></div>
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<p><a name="doc_002dismatrix"></a>
<div class="defun">
— Built-in Function: <b>ismatrix</b> (<var>a</var>)<var><a name="index-ismatrix-271"></a></var><br>
<blockquote><p>Return 1 if <var>a</var> is a matrix. Otherwise, return 0.
</p></blockquote></div>
<!-- ./general/isvector.m -->
<p><a name="doc_002disvector"></a>
<div class="defun">
— Function File: <b>isvector</b> (<var>a</var>)<var><a name="index-isvector-272"></a></var><br>
<blockquote><p>Return 1 if <var>a</var> is a vector. Otherwise, return 0.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsize.html#doc_002dsize">size</a>, <a href="doc_002drows.html#doc_002drows">rows</a>, <a href="doc_002dcolumns.html#doc_002dcolumns">columns</a>, <a href="doc_002dlength.html#doc_002dlength">length</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>.
</p></blockquote></div>
<!-- ./general/isscalar.m -->
<p><a name="doc_002disscalar"></a>
<div class="defun">
— Function File: <b>isscalar</b> (<var>a</var>)<var><a name="index-isscalar-273"></a></var><br>
<blockquote><p>Return 1 if <var>a</var> is a scalar. Otherwise, return 0.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsize.html#doc_002dsize">size</a>, <a href="doc_002drows.html#doc_002drows">rows</a>, <a href="doc_002dcolumns.html#doc_002dcolumns">columns</a>, <a href="doc_002dlength.html#doc_002dlength">length</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>.
</p></blockquote></div>
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<p><a name="doc_002dissquare"></a>
<div class="defun">
— Function File: <b>issquare</b> (<var>x</var>)<var><a name="index-issquare-274"></a></var><br>
<blockquote><p>If <var>x</var> is a square matrix, then return the dimension of <var>x</var>.
Otherwise, return 0.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsize.html#doc_002dsize">size</a>, <a href="doc_002drows.html#doc_002drows">rows</a>, <a href="doc_002dcolumns.html#doc_002dcolumns">columns</a>, <a href="doc_002dlength.html#doc_002dlength">length</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>.
</p></blockquote></div>
<!-- ./general/issymmetric.m -->
<p><a name="doc_002dissymmetric"></a>
<div class="defun">
— Function File: <b>issymmetric</b> (<var>x, tol</var>)<var><a name="index-issymmetric-275"></a></var><br>
<blockquote><p>If <var>x</var> is symmetric within the tolerance specified by <var>tol</var>,
then return the dimension of <var>x</var>. Otherwise, return 0. If
<var>tol</var> is omitted, use a tolerance equal to the machine precision.
Matrix <var>x</var> is considered symmetric if
<code>norm (</code><var>x</var><code> - </code><var>x</var><code>.', inf) / norm (</code><var>x</var><code>, inf) < </code><var>tol</var>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsize.html#doc_002dsize">size</a>, <a href="doc_002drows.html#doc_002drows">rows</a>, <a href="doc_002dcolumns.html#doc_002dcolumns">columns</a>, <a href="doc_002dlength.html#doc_002dlength">length</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002dissquare.html#doc_002dissquare">issquare</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>.
</p></blockquote></div>
<!-- ./general/isdefinite.m -->
<p><a name="doc_002disdefinite"></a>
<div class="defun">
— Function File: <b>isdefinite</b> (<var>x, tol</var>)<var><a name="index-isdefinite-276"></a></var><br>
<blockquote><p>Return 1 if <var>x</var> is symmetric positive definite within the
tolerance specified by <var>tol</var> or 0 if <var>x</var> is symmetric
positive semidefinite. Otherwise, return -1. If <var>tol</var>
is omitted, use a tolerance equal to 100 times the machine precision.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dissymmetric.html#doc_002dissymmetric">issymmetric</a>.
</p></blockquote></div>
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<p><a name="doc_002dislogical"></a>
<div class="defun">
— Built-in Function: <b>islogical</b> (<var>x</var>)<var><a name="index-islogical-277"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a logical object.
</p></blockquote></div>
<!-- ./specfun/isprime.m -->
<p><a name="doc_002disprime"></a>
<div class="defun">
— Function File: <b>isprime</b> (<var>n</var>)<var><a name="index-isprime-278"></a></var><br>
<blockquote>
<p>Return true if <var>n</var> is a prime number, false otherwise.
<p>Something like the following is much faster if you need to test a lot
of small numbers:
<pre class="example"> <var>t</var> = ismember (<var>n</var>, primes (max (<var>n</var> (:))));
</pre>
<p>If max(n) is very large, then you should be using special purpose
factorization code.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dprimes.html#doc_002dprimes">primes</a>, <a href="doc_002dfactor.html#doc_002dfactor">factor</a>, <a href="doc_002dgcd.html#doc_002dgcd">gcd</a>, <a href="doc_002dlcm.html#doc_002dlcm">lcm</a>.
</p></blockquote></div>
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