<HTML ><HEAD ><TITLE >log</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="PHP Manual" HREF="index.html"><LINK REL="UP" TITLE="Mathematical Functions" HREF="ref.math.html"><LINK REL="PREVIOUS" TITLE="log1p" HREF="function.log1p.html"><LINK REL="NEXT" TITLE="max" HREF="function.max.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=ISO-8859-1"></HEAD ><BODY CLASS="refentry" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.log1p.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.max.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.log" ></A >log</H1 ><DIV CLASS="refnamediv" ><A NAME="AEN44910" ></A ><P > (PHP 3, PHP 4 )</P >log -- Natural logarithm</DIV ><DIV CLASS="refsect1" ><A NAME="AEN44913" ></A ><H2 >Description</H2 >float <B CLASS="methodname" >log</B > ( float arg [, float base])<BR ></BR ><P > If the optional <TT CLASS="parameter" ><I >base</I ></TT > parameter is specified, <B CLASS="function" >log()</B > returns log<SUB >base</SUB > <TT CLASS="parameter" ><I >arg</I ></TT >, otherwise <B CLASS="function" >log()</B > returns the natural logarithm of <TT CLASS="parameter" ><I >arg</I ></TT >. </P ><DIV CLASS="note" ><BLOCKQUOTE CLASS="note" ><P ><B >Note: </B > The <TT CLASS="parameter" ><I >base</I ></TT > parameter became available with PHP version 4.3.0. </P ><P > As always you can calculate the logarithm in base <TT CLASS="literal" >b</TT > of a number <TT CLASS="literal" >n</TT >, but using the mathematical identity: log<SUB >b</SUB >(n) = log(n)/log(b), where log is the neperian (or natural) logarithm. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="function.log1p.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.max.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >log1p</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ref.math.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >max</TD ></TR ></TABLE ></DIV ></BODY ></HTML >