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<HTML><HEAD><TITLE>Recipe 2.11. Doing Trigonometry in Degrees, not Radians (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:30:15Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch02_01.htm"TITLE="2. Numbers"><LINKREL="prev"HREF="ch02_11.htm"TITLE="2.10. Generating Biased Random Numbers"><LINKREL="next"HREF="ch02_13.htm"TITLE="2.12. Calculating More Trigonometric Functions"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_11.htm"TITLE="2.10. Generating Biased Random Numbers"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 2.10. Generating Biased Random Numbers"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch02_01.htm"TITLE="2. Numbers"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_13.htm"TITLE="2.12. Calculating More Trigonometric Functions"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 2.12. Calculating More Trigonometric Functions"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch02-chap02_doing_0">2.11. Doing Trigonometry in Degrees, not Radians</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-797">Problem <ACLASS="indexterm"NAME="ch02-idx-1000008061-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008061-1"></A><ACLASS="indexterm"NAME="ch02-idx-1000008061-2"></A><ACLASS="indexterm"NAME="ch02-idx-1000008061-3"></A><ACLASS="indexterm"NAME="ch02-idx-1000008061-4"></A><ACLASS="indexterm"NAME="ch02-idx-1000008061-5"></A></A></H3><PCLASS="para">You want your trigonometry routines to operate in degrees instead of Perl's native radians.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-803">Solution</A></H3><PCLASS="para">Convert between radians and degrees (2<IMGSRC="../chars/pi.gif"ALT="[pi]"> radians equals 360 degrees).</P><PRECLASS="programlisting">BEGIN { use constant PI => 3.14159265358979; sub deg2rad { my $degrees = shift; return ($degrees / 180) * PI; } sub rad2deg { my $radians = shift; return ($radians / PI) * 180; }}</PRE><PCLASS="para">Alternatively, use the <ACLASS="indexterm"NAME="ch02-idx-1000008067-0"></A>Math::Trig module.</P><PRECLASS="programlisting">use Math::Trig;$radians = deg2rad($degrees);$degrees = rad2deg($radians);</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-845">Discussion</A></H3><PCLASS="para">If you're doing a lot of trigonometry, look into using either the standard Math::Trig or POSIX modules. They provide many more trigonometric functions than are defined in the Perl core. Otherwise, the first solution above will define the <CODECLASS="literal">rad2deg</CODE><ACLASS="indexterm"NAME="ch02-idx-1000008068-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008068-1"></A> and <CODECLASS="literal">deg2rad</CODE> functions. The value of <IMGSRC="../chars/pi.gif"ALT="[pi]"> isn't built directly into Perl, but you can calculate it to as much precision as your floating-point hardware provides. If you put it in a BEGIN block, this is done at compile time. In the solution above, the <CODECLASS="literal">PI</CODE> function is a constant created with <CODECLASS="literal">use</CODE> <CODECLASS="literal">constant</CODE>.</P><PCLASS="para">If you're looking for the sine in degrees, use this:</P><PRECLASS="programlisting"># deg2rad and rad2deg defined either as above or from Math::Trigsub degree_sine { my $degrees = shift; my $radians = deg2rad($degrees); my $result = sin($radians); return $result;}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-871">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">sin</CODE>, <CODECLASS="literal">cos</CODE>, and <CODECLASS="literal">atan2</CODE> functions in <EMCLASS="emphasis">perlfunc</EM> (1) and <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; the documentation for the standard POSIX and Math::Trig modules (also in <ACLASS="olink"HREF="../prog/ch07_01.htm">Chapter 7</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>) <ACLASS="indexterm"NAME="ch02-idx-1000008063-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008063-1"></A><ACLASS="indexterm"NAME="ch02-idx-1000008063-2"></A><ACLASS="indexterm"NAME="ch02-idx-1000008063-3"></A><ACLASS="indexterm"NAME="ch02-idx-1000008063-4"></A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_11.htm"TITLE="2.10. 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Calculating More Trigonometric Functions</TD></TR></TABLE><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><FONTSIZE="-1"></DIV<!-- LIBRARY NAV BAR --> <img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p> <a href="copyrght.htm">Copyright © 2002</a> O'Reilly & Associates. All rights reserved.</font> </p> <map name="library-map"> <area shape="rect" coords="1,0,85,94" href="../index.htm"><area shape="rect" coords="86,1,178,103" href="../lwp/index.htm"><area shape="rect" coords="180,0,265,103" href="../lperl/index.htm"><area shape="rect" coords="267,0,353,105" href="../perlnut/index.htm"><area shape="rect" coords="354,1,446,115" href="../prog/index.htm"><area shape="rect" coords="448,0,526,132" href="../tk/index.htm"><area shape="rect" coords="528,1,615,119" href="../cookbook/index.htm"><area shape="rect" coords="617,0,690,135" href="../pxml/index.htm"></map> </BODY></HTML>⌨️ 快捷键说明
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