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| <h3 class="section">1.14 <code>erf</code>, <code>erff</code>, <code>erfc</code>, <code>erfcf</code>—error function</h3> |
| |
| <p><a name="index-erf-35"></a><a name="index-erff-36"></a><a name="index-erfc-37"></a><a name="index-erfcf-38"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <math.h> |
| double erf(double <var>x</var>); |
| float erff(float <var>x</var>); |
| double erfc(double <var>x</var>); |
| float erfcf(float <var>x</var>); |
| </pre> |
| <p><strong>Description</strong><br> |
| <code>erf</code> calculates an approximation to the “error function”, |
| which estimates the probability that an observation will fall within |
| <var>x</var> standard deviations of the mean (assuming a normal |
| distribution). |
| |
| <p><code>erfc</code> calculates the complementary probability; that is, |
| <code>erfc(</code><var>x</var><code>)</code> is <code>1 - erf(</code><var>x</var><code>)</code>. <code>erfc</code> is computed directly, |
| so that you can use it to avoid the loss of precision that would |
| result from subtracting large probabilities (on large <var>x</var>) from 1. |
| |
| <p><code>erff</code> and <code>erfcf</code> differ from <code>erf</code> and <code>erfc</code> only in the |
| argument and result types. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| For positive arguments, <code>erf</code> and all its variants return a |
| probability—a number between 0 and 1. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| None of the variants of <code>erf</code> are ANSI C. |
| |
| <p><br> |
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