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<title>GNU Scientific Library – Reference Manual: Digamma Function</title>
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Next: <a href="Trigamma-Function.html#Trigamma-Function" accesskey="n" rel="next">Trigamma Function</a>, Up: <a href="Psi-_0028Digamma_0029-Function.html#Psi-_0028Digamma_0029-Function" accesskey="u" rel="up">Psi (Digamma) Function</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Digamma-Function-1"></a>
<h4 class="subsection">7.28.1 Digamma Function</h4>
<dl>
<dt><a name="index-gsl_005fsf_005fpsi_005fint"></a>Function: <em>double</em> <strong>gsl_sf_psi_int</strong> <em>(int <var>n</var>)</em></dt>
<dt><a name="index-gsl_005fsf_005fpsi_005fint_005fe"></a>Function: <em>int</em> <strong>gsl_sf_psi_int_e</strong> <em>(int <var>n</var>, gsl_sf_result * <var>result</var>)</em></dt>
<dd><p>These routines compute the digamma function <em>\psi(n)</em> for positive
integer <var>n</var>. The digamma function is also called the Psi function.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fsf_005fpsi"></a>Function: <em>double</em> <strong>gsl_sf_psi</strong> <em>(double <var>x</var>)</em></dt>
<dt><a name="index-gsl_005fsf_005fpsi_005fe"></a>Function: <em>int</em> <strong>gsl_sf_psi_e</strong> <em>(double <var>x</var>, gsl_sf_result * <var>result</var>)</em></dt>
<dd><p>These routines compute the digamma function <em>\psi(x)</em> for general
<em>x</em>, <em>x \ne 0</em>.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fsf_005fpsi_005f1piy"></a>Function: <em>double</em> <strong>gsl_sf_psi_1piy</strong> <em>(double <var>y</var>)</em></dt>
<dt><a name="index-gsl_005fsf_005fpsi_005f1piy_005fe"></a>Function: <em>int</em> <strong>gsl_sf_psi_1piy_e</strong> <em>(double <var>y</var>, gsl_sf_result * <var>result</var>)</em></dt>
<dd><p>These routines compute the real part of the digamma function on the line
<em>1+i y</em>, <em>\Re[\psi(1 + i y)]</em>.
</p></dd></dl>
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