20.3 Example Program: Roots of a Polynomial

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NOTE -- This program is in the file complx.cpp.

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The roots of a polynomial are given by the formula:

The following function takes as input three double precision numbers, and returns the complex roots as a pair of values.

typedef std::complex<double> dcomplex;

std::pair<dcomplex, dcomplex> quadratic
      (dcomplex a, dcomplex b, dcomplex c)
// return the roots of a quadratic equation
{
   dcomplex root = std::sqrt(b * b - 4.0 * a * c);
   a *= 2.0;
   return std::make_pair( (-b + root)/a, 
                          (-b - root)/a );
}