| /* poly/zsolve_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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| */ |
| |
| /* complex_solve_quadratic.c - finds complex roots of a x^2 + b x + c = 0 */ |
| |
| #include <config.h> |
| #include <math.h> |
| #include <gsl/gsl_complex.h> |
| #include <gsl/gsl_poly.h> |
| |
| int |
| gsl_poly_complex_solve_quadratic (double a, double b, double c, |
| gsl_complex *z0, gsl_complex *z1) |
| { |
| double disc = b * b - 4 * a * c; |
| |
| if (a == 0) /* Handle linear case */ |
| { |
| if (b == 0) |
| { |
| return 0; |
| } |
| else |
| { |
| GSL_REAL(*z0) = -c / b; |
| GSL_IMAG(*z0) = 0; |
| return 1; |
| }; |
| } |
| |
| if (disc > 0) |
| { |
| if (b == 0) |
| { |
| double s = fabs (0.5 * sqrt (disc) / a); |
| GSL_REAL (*z0) = -s; |
| GSL_IMAG (*z0) = 0; |
| GSL_REAL (*z1) = s; |
| GSL_IMAG (*z1) = 0; |
| } |
| 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) |
| { |
| GSL_REAL (*z0) = r1; |
| GSL_IMAG (*z0) = 0; |
| GSL_REAL (*z1) = r2; |
| GSL_IMAG (*z1) = 0; |
| } |
| else |
| { |
| GSL_REAL (*z0) = r2; |
| GSL_IMAG (*z0) = 0; |
| GSL_REAL (*z1) = r1; |
| GSL_IMAG (*z1) = 0; |
| } |
| } |
| return 2; |
| } |
| else if (disc == 0) |
| { |
| GSL_REAL (*z0) = -0.5 * b / a; |
| GSL_IMAG (*z0) = 0; |
| |
| GSL_REAL (*z1) = -0.5 * b / a; |
| GSL_IMAG (*z1) = 0; |
| |
| return 2; |
| } |
| else |
| { |
| double s = fabs (0.5 * sqrt (-disc) / a); |
| |
| GSL_REAL (*z0) = -0.5 * b / a; |
| GSL_IMAG (*z0) = -s; |
| |
| GSL_REAL (*z1) = -0.5 * b / a; |
| GSL_IMAG (*z1) = s; |
| |
| return 2; |
| } |
| } |