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<title>GNU Scientific Library – Reference Manual: Mathematical Constants</title>
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<p>
Next: <a href="Infinities-and-Not_002da_002dnumber.html#Infinities-and-Not_002da_002dnumber" accesskey="n" rel="next">Infinities and Not-a-number</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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<hr>
<a name="Mathematical-Constants-1"></a>
<h3 class="section">4.1 Mathematical Constants</h3>
<a name="index-mathematical-constants_002c-defined-as-macros"></a>
<a name="index-numerical-constants_002c-defined-as-macros"></a>
<a name="index-constants_002c-mathematical_002d_002d_002ddefined-as-macros"></a>
<a name="index-macros-for-mathematical-constants"></a>
<p>The library ensures that the standard <small>BSD</small> mathematical constants
are defined. For reference, here is a list of the constants:
</p>
<dl compact="compact">
<dt><code>M_E</code></dt>
<dd><a name="index-e_002c-defined-as-a-macro"></a>
<p>The base of exponentials, <em>e</em>
</p>
</dd>
<dt><code>M_LOG2E</code></dt>
<dd><p>The base-2 logarithm of <em>e</em>, <em>\log_2 (e)</em>
</p>
</dd>
<dt><code>M_LOG10E</code></dt>
<dd><p>The base-10 logarithm of <em>e</em>, <em>\log_10 (e)</em>
</p>
</dd>
<dt><code>M_SQRT2</code></dt>
<dd><p>The square root of two, <em>\sqrt 2</em>
</p>
</dd>
<dt><code>M_SQRT1_2</code></dt>
<dd><p>The square root of one-half, <em>\sqrt{1/2}</em>
</p>
</dd>
<dt><code>M_SQRT3</code></dt>
<dd><p>The square root of three, <em>\sqrt 3</em>
</p>
</dd>
<dt><code>M_PI</code></dt>
<dd><a name="index-pi_002c-defined-as-a-macro"></a>
<p>The constant pi, <em>\pi</em>
</p>
</dd>
<dt><code>M_PI_2</code></dt>
<dd><p>Pi divided by two, <em>\pi/2</em>
</p>
</dd>
<dt><code>M_PI_4</code></dt>
<dd><p>Pi divided by four, <em>\pi/4</em>
</p>
</dd>
<dt><code>M_SQRTPI</code></dt>
<dd><p>The square root of pi, <em>\sqrt\pi</em>
</p>
</dd>
<dt><code>M_2_SQRTPI</code></dt>
<dd><p>Two divided by the square root of pi, <em>2/\sqrt\pi</em>
</p>
</dd>
<dt><code>M_1_PI</code></dt>
<dd><p>The reciprocal of pi, <em>1/\pi</em>
</p>
</dd>
<dt><code>M_2_PI</code></dt>
<dd><p>Twice the reciprocal of pi, <em>2/\pi</em>
</p>
</dd>
<dt><code>M_LN10</code></dt>
<dd><p>The natural logarithm of ten, <em>\ln(10)</em>
</p>
</dd>
<dt><code>M_LN2</code></dt>
<dd><p>The natural logarithm of two, <em>\ln(2)</em>
</p>
</dd>
<dt><code>M_LNPI</code></dt>
<dd><p>The natural logarithm of pi, <em>\ln(\pi)</em>
</p>
</dd>
<dt><code>M_EULER</code></dt>
<dd><a name="index-Euler_0027s-constant_002c-defined-as-a-macro"></a>
<p>Euler’s constant, <em>\gamma</em>
</p>
</dd>
</dl>
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