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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>expm1</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_004_083"> </a>NAME</h4><blockquote>expm1 - compute exponential functions</blockquote><h4><a name = "tag_000_004_084"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="math.h.html">math.h</a>>double expm1 (double <i>x</i>);</code></pre></blockquote><h4><a name = "tag_000_004_085"> </a>DESCRIPTION</h4><blockquote>The<i>expm1()</i>function computes <i>e</i><sup><small><i>x</i></small></sup>-1.0.</blockquote><h4><a name = "tag_000_004_086"> </a>RETURN VALUE</h4><blockquote><p>If <i>x</i> is NaN, then the function returns NaN and <i>errno</i>may be set to EDOM.<p>If <i>x</i> is positive infinity,<i>expm1()</i>returns positive infinity.<p>If <i>x</i> is negative infinity,<i>expm1()</i>returns -1.0.<p>If the value overflows,<i>expm1()</i>returns HUGE_VAL and may set <i>errno</i> to ERANGE.</blockquote><h4><a name = "tag_000_004_087"> </a>ERRORS</h4><blockquote>The<i>expm1()</i>function may fail if:<dl compact><dt>[EDOM]<dd>The value of <i>x</i> is NaN.<dt>[ERANGE]<dd>The result overflows.</dl></blockquote><h4><a name = "tag_000_004_088"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_004_089"> </a>APPLICATION USAGE</h4><blockquote>The value of<i>expm1</i>(<i>x</i>)may be more accurate than<i>exp</i>(<i>x</i>)-1.0for small values of<i>x</i>.<p>The<i>expm1()</i>and<i><a href="log1p.html">log1p()</a></i>functions are useful for financial calculations of((1+<i>x</i>)<sup><small><i>n</i></small></sup>-1)/<i>x</i>, namely:<pre><dl compact><dt> <dd>expm1(<i>n</i> * log1p(<i>x</i>))/<i>x</i></dl></pre>when <i>x</i> is very small (for example, when calculating smalldaily interest rates). These functions also simplify writingaccurate inverse hyperbolic functions.</blockquote><h4><a name = "tag_000_004_090"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_004_091"> </a>SEE ALSO</h4><blockquote><i><a href="exp.html">exp()</a></i>,<i><a href="ilogb.html">ilogb()</a></i>,<i><a href="log1p.html">log1p()</a></i>,<i><a href="math.h.html"><math.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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