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<HTML>
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<HEAD>
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<TITLE>Example Program: Roots of a Polynomial</TITLE>
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<H2>20.3 Example Program: Roots of a Polynomial</H2>
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<A NAME="idx445"><!></A>
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<BLOCKQUOTE><HR><B>
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NOTE -- This program is in the file complx.cpp.
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</B><HR></BLOCKQUOTE>
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<P>The roots of a polynomial <IMG SRC="images/stdlibug-SpecialClassesa.gif" WIDTH=128 HEIGHT=29>are given by the formula:</P>
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<P><IMG SRC="images/stdlibug-SpecialClasses2.gif" WIDTH=177 HEIGHT=71></P>
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<P>The following function takes as input three double precision numbers, and returns the complex roots as a pair of values.</P>
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<UL><PRE>
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typedef std::complex<double> dcomplex;
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std::pair<dcomplex, dcomplex> quadratic
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(dcomplex a, dcomplex b, dcomplex c)
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// return the roots of a quadratic equation
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{
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dcomplex root = std::sqrt(b * b - 4.0 * a * c);
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a *= 2.0;
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return std::make_pair( (-b + root)/a,
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(-b - root)/a );
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}
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