3 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Reid Priedhorsky, Brian Gough
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 3 of the License, or (at
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11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
21 /* bisection.c -- bisection root finding algorithm */
31 #include <gsl/gsl_math.h>
32 #include <gsl/gsl_errno.h>
33 #include <gsl/gsl_roots.h>
39 double f_lower, f_upper;
43 static int bisection_init (void * vstate, gsl_function * f, double * root, double x_lower, double x_upper);
44 static int bisection_iterate (void * vstate, gsl_function * f, double * root, double * x_lower, double * x_upper);
47 bisection_init (void * vstate, gsl_function * f, double * root, double x_lower, double x_upper)
49 bisection_state_t * state = (bisection_state_t *) vstate;
51 double f_lower, f_upper ;
53 *root = 0.5 * (x_lower + x_upper) ;
55 SAFE_FUNC_CALL (f, x_lower, &f_lower);
56 SAFE_FUNC_CALL (f, x_upper, &f_upper);
58 state->f_lower = f_lower;
59 state->f_upper = f_upper;
61 if ((f_lower < 0.0 && f_upper < 0.0) || (f_lower > 0.0 && f_upper > 0.0))
63 GSL_ERROR ("endpoints do not straddle y=0", GSL_EINVAL);
71 bisection_iterate (void * vstate, gsl_function * f, double * root, double * x_lower, double * x_upper)
73 bisection_state_t * state = (bisection_state_t *) vstate;
75 double x_bisect, f_bisect;
77 const double x_left = *x_lower ;
78 const double x_right = *x_upper ;
80 const double f_lower = state->f_lower;
81 const double f_upper = state->f_upper;
97 x_bisect = (x_left + x_right) / 2.0;
99 SAFE_FUNC_CALL (f, x_bisect, &f_bisect);
109 /* Discard the half of the interval which doesn't contain the root. */
111 if ((f_lower > 0.0 && f_bisect < 0.0) || (f_lower < 0.0 && f_bisect > 0.0))
113 *root = 0.5 * (x_left + x_bisect) ;
115 state->f_upper = f_bisect;
119 *root = 0.5 * (x_bisect + x_right) ;
121 state->f_lower = f_bisect;
128 static const gsl_root_fsolver_type bisection_type =
129 {"bisection", /* name */
130 sizeof (bisection_state_t),
134 const gsl_root_fsolver_type * gsl_root_fsolver_bisection = &bisection_type;