solve_quadratic.c

开放gsl矩阵运算

/* poly/solve_quadratic.c
 * 
 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Brian Gough
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/* solve_quadratic.c - finds the real roots of a x^2 + b x + c = 0 */

#include <config.h>
#include <math.h>

#include <gsl/gsl_poly.h>

int 
gsl_poly_solve_quadratic (double a, double b, double c, 
                          double *x0, double *x1)
{
  double disc = b * b - 4 * a * c;

  if (disc > 0)
    {
      if (b == 0)
	{
          double r = fabs (0.5 * sqrt (disc) / a);
	  *x0 = -r;
	  *x1 =  r;
	}
      else
	{
	  double sgnb = (b > 0 ? 1 : -1);
	  double temp = -0.5 * (b + sgnb * sqrt (disc));
	  double r1 = temp / a ;
	  double r2 = c / temp ;

	  if (r1 < r2) 
	    {
	      *x0 = r1 ;
	      *x1 = r2 ;
	    } 
	  else 
	    {
	      *x0 = r2 ;
	      *x1 = r1 ;
	    }
	}
      return 2;
    }
  else if (disc == 0) 
    {
      *x0 = -0.5 * b / a ;
      *x1 = -0.5 * b / a ;
      return 2 ;
    }
  else
    {
      return 0;
    }
}