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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>,
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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.
<!-- isnumeric src/data.cc -->
<p><a name="doc_002disnumeric"></a>
<div class="defun">
— Built-in Function: <b>isnumeric</b> (<var>x</var>)<var><a name="index-isnumeric-302"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a numeric object, i.e., an integer, real, or
complex array. Logical and character arrays are not considered to be
numeric.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disinteger.html#doc_002disinteger">isinteger</a>, <a href="doc_002disfloat.html#doc_002disfloat">isfloat</a>, <a href="doc_002disreal.html#doc_002disreal">isreal</a>, <a href="doc_002discomplex.html#doc_002discomplex">iscomplex</a>, <a href="doc_002dislogical.html#doc_002dislogical">islogical</a>, <a href="doc_002dischar.html#doc_002dischar">ischar</a>, <a href="doc_002discell.html#doc_002discell">iscell</a>, <a href="doc_002disstruct.html#doc_002disstruct">isstruct</a>.
</p></blockquote></div>
<!-- isfloat src/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-303"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a floating-point numeric object.
Objects of class double or single are floating-point objects.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disinteger.html#doc_002disinteger">isinteger</a>, <a href="doc_002dischar.html#doc_002dischar">ischar</a>, <a href="doc_002dislogical.html#doc_002dislogical">islogical</a>, <a href="doc_002disnumeric.html#doc_002disnumeric">isnumeric</a>, <a href="doc_002disa.html#doc_002disa">isa</a>.
</p></blockquote></div>
<!-- isreal src/data.cc -->
<p><a name="doc_002disreal"></a>
<div class="defun">
— Built-in Function: <b>isreal</b> (<var>x</var>)<var><a name="index-isreal-304"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a non-complex matrix or scalar.
For compatibility with <span class="sc">matlab</span>, this includes logical and character
matrices.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002discomplex.html#doc_002discomplex">iscomplex</a>, <a href="doc_002disnumeric.html#doc_002disnumeric">isnumeric</a>.
</p></blockquote></div>
<!-- iscomplex src/data.cc -->
<p><a name="doc_002discomplex"></a>
<div class="defun">
— Built-in Function: <b>iscomplex</b> (<var>x</var>)<var><a name="index-iscomplex-305"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a complex-valued numeric object.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disreal.html#doc_002disreal">isreal</a>, <a href="doc_002disnumeric.html#doc_002disnumeric">isnumeric</a>.
</p></blockquote></div>
<!-- ismatrix src/data.cc -->
<p><a name="doc_002dismatrix"></a>
<div class="defun">
— Built-in Function: <b>ismatrix</b> (<var>a</var>)<var><a name="index-ismatrix-306"></a></var><br>
<blockquote><p>Return true if <var>a</var> is a numeric, logical, or character matrix.
Scalars (1x1 matrices) and vectors (1xN or Nx1 matrices)
are subsets of the more general N-dimensional matrix and <code>ismatrix</code>
will return true for these objects as well.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>, <a href="doc_002discell.html#doc_002discell">iscell</a>, <a href="doc_002disstruct.html#doc_002disstruct">isstruct</a>, <a href="doc_002dissparse.html#doc_002dissparse">issparse</a>.
</p></blockquote></div>
<!-- isvector scripts/general/isvector.m -->
<p><a name="doc_002disvector"></a>
<div class="defun">
— Function File: <b>isvector</b> (<var>x</var>)<var><a name="index-isvector-307"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a vector. A vector is a 2-D array
where one of the dimensions is equal to 1. As a consequence a
1x1 array, or scalar, is also a vector.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>, <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>.
</p></blockquote></div>
<!-- isrow scripts/general/isrow.m -->
<p><a name="doc_002disrow"></a>
<div class="defun">
— Function File: <b>isrow</b> (<var>x</var>)<var><a name="index-isrow-308"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a row vector.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002discolumn.html#doc_002discolumn">iscolumn</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>.
</p></blockquote></div>
<!-- iscolumn scripts/general/iscolumn.m -->
<p><a name="doc_002discolumn"></a>
<div class="defun">
— Function File: <b>iscolumn</b> (<var>x</var>)<var><a name="index-iscolumn-309"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a column vector.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disrow.html#doc_002disrow">isrow</a>, <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>.
</p></blockquote></div>
<!-- isscalar scripts/general/isscalar.m -->
<p><a name="doc_002disscalar"></a>
<div class="defun">
— Function File: <b>isscalar</b> (<var>x</var>)<var><a name="index-isscalar-310"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a scalar.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disvector.html#doc_002disvector">isvector</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>.
</p></blockquote></div>
<!-- issquare scripts/general/issquare.m -->
<p><a name="doc_002dissquare"></a>
<div class="defun">
— Function File: <b>issquare</b> (<var>x</var>)<var><a name="index-issquare-311"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a square matrix.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disscalar.html#doc_002disscalar">isscalar</a>, <a href="doc_002disvector.html#doc_002disvector">isvector</a>, <a href="doc_002dismatrix.html#doc_002dismatrix">ismatrix</a>, <a href="doc_002dsize.html#doc_002dsize">size</a>.
</p></blockquote></div>
<!-- issymmetric scripts/linear-algebra/issymmetric.m -->
<p><a name="doc_002dissymmetric"></a>
<div class="defun">
— Function File: <b>issymmetric</b> (<var>x</var>)<var><a name="index-issymmetric-312"></a></var><br>
— Function File: <b>issymmetric</b> (<var>x, tol</var>)<var><a name="index-issymmetric-313"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a symmetric matrix within the tolerance specified
by <var>tol</var>. The default tolerance is zero (uses faster code).
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_002dishermitian.html#doc_002dishermitian">ishermitian</a>, <a href="doc_002disdefinite.html#doc_002disdefinite">isdefinite</a>.
</p></blockquote></div>
<!-- ishermitian scripts/linear-algebra/ishermitian.m -->
<p><a name="doc_002dishermitian"></a>
<div class="defun">
— Function File: <b>ishermitian</b> (<var>x</var>)<var><a name="index-ishermitian-314"></a></var><br>
— Function File: <b>ishermitian</b> (<var>x, tol</var>)<var><a name="index-ishermitian-315"></a></var><br>
<blockquote><p>Return true if <var>x</var> is Hermitian within the tolerance specified by
<var>tol</var>.
The default tolerance is zero (uses faster code).
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_002dissymmetric.html#doc_002dissymmetric">issymmetric</a>, <a href="doc_002disdefinite.html#doc_002disdefinite">isdefinite</a>.
</p></blockquote></div>
<!-- isdefinite scripts/linear-algebra/isdefinite.m -->
<p><a name="doc_002disdefinite"></a>
<div class="defun">
— Function File: <b>isdefinite</b> (<var>x</var>)<var><a name="index-isdefinite-316"></a></var><br>
— Function File: <b>isdefinite</b> (<var>x, tol</var>)<var><a name="index-isdefinite-317"></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 of
<code>100 * eps * norm (</code><var>x</var><code>, "fro")</code>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dissymmetric.html#doc_002dissymmetric">issymmetric</a>, <a href="doc_002dishermitian.html#doc_002dishermitian">ishermitian</a>.
</p></blockquote></div>
<!-- islogical src/data.cc -->
<p><a name="doc_002dislogical"></a>
<div class="defun">
— Built-in Function: <b>islogical</b> (<var>x</var>)<var><a name="index-islogical-318"></a></var><br>
— Built-in Function: <b>isbool</b> (<var>x</var>)<var><a name="index-isbool-319"></a></var><br>
<blockquote><p>Return true if <var>x</var> is a logical object.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002disfloat.html#doc_002disfloat">isfloat</a>, <a href="doc_002disinteger.html#doc_002disinteger">isinteger</a>, <a href="doc_002dischar.html#doc_002dischar">ischar</a>, <a href="doc_002disnumeric.html#doc_002disnumeric">isnumeric</a>, <a href="doc_002disa.html#doc_002disa">isa</a>.
</p></blockquote></div>
<!-- isprime scripts/specfun/isprime.m -->
<p><a name="doc_002disprime"></a>
<div class="defun">
— Function File: <b>isprime</b> (<var>x</var>)<var><a name="index-isprime-320"></a></var><br>
<blockquote><p>Return a logical array which is true where the elements of <var>x</var> are
prime numbers and false where they are not.
<p>If the maximum value in <var>x</var> is very large, then you should be using
special purpose factorization code.
<pre class="example"> isprime (1:6)
⇒ [0, 1, 1, 0, 1, 0]
</pre>
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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>
<p>If instead of knowing properties of variables, you wish to know which
variables are defined and to gather other information about the
workspace itself, see <a href="Status-of-Variables.html#Status-of-Variables">Status of Variables</a>.
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