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<title>GNU Scientific Library – Reference Manual: Small integer powers</title>
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<a name="Small-integer-powers"></a>
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Next: <a href="Testing-the-Sign-of-Numbers.html#Testing-the-Sign-of-Numbers" accesskey="n" rel="next">Testing the Sign of Numbers</a>, Previous: <a href="Elementary-Functions.html#Elementary-Functions" accesskey="p" rel="previous">Elementary Functions</a>, Up: <a href="Mathematical-Functions.html#Mathematical-Functions" accesskey="u" rel="up">Mathematical Functions</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Small-integer-powers-1"></a>
<h3 class="section">4.4 Small integer powers</h3>
<p>A common complaint about the standard C library is its lack of a
function for calculating (small) integer powers. GSL provides some simple
functions to fill this gap. For reasons of efficiency, these functions
do not check for overflow or underflow conditions.
</p>
<dl>
<dt><a name="index-gsl_005fpow_005fint"></a>Function: <em>double</em> <strong>gsl_pow_int</strong> <em>(double <var>x</var>, int <var>n</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005fuint"></a>Function: <em>double</em> <strong>gsl_pow_uint</strong> <em>(double <var>x</var>, unsigned int <var>n</var>)</em></dt>
<dd><p>These routines computes the power <em>x^n</em> for integer <var>n</var>. The
power is computed efficiently—for example, <em>x^8</em> is computed as
<em>((x^2)^2)^2</em>, requiring only 3 multiplications. A version of this
function which also computes the numerical error in the result is
available as <code>gsl_sf_pow_int_e</code>.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fpow_005f2"></a>Function: <em>double</em> <strong>gsl_pow_2</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f3"></a>Function: <em>double</em> <strong>gsl_pow_3</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f4"></a>Function: <em>double</em> <strong>gsl_pow_4</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f5"></a>Function: <em>double</em> <strong>gsl_pow_5</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f6"></a>Function: <em>double</em> <strong>gsl_pow_6</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f7"></a>Function: <em>double</em> <strong>gsl_pow_7</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f8"></a>Function: <em>double</em> <strong>gsl_pow_8</strong> <em>(const double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fpow_005f9"></a>Function: <em>double</em> <strong>gsl_pow_9</strong> <em>(const double <var>x</var>)</em></dt>
<dd><p>These functions can be used to compute small integer powers <em>x^2</em>,
<em>x^3</em>, etc. efficiently. The functions will be inlined when
<code>HAVE_INLINE</code> is defined, so that use of these functions
should be as efficient as explicitly writing the corresponding
product expression.
</p></dd></dl>
<div class="example">
<pre class="example">#include <gsl/gsl_math.h>
double y = gsl_pow_4 (3.141) /* compute 3.141**4 */
</pre></div>
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