20.3 Example Program: Roots of a Polynomial

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

The roots of a polynomial are given by the formula:

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

typedef complex<double> dcomplex;

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