Re: core

[Brian Gough <bjg@network-theory.co.uk>]

Hi,
The definition of gsl_function was changed to allow additional
parameters (such as a) to be passed to the function without the use of
static variables. See the latest doc/roots.texi file in CVS for an
example of how to use gsl_function. Also, the line x = NULL is a
problem, since x must point to allocated memory. Try *x = 0 instead.

regards
Brian Gough

Rodolphe Pollet writes:
 > 
 > This is a simple code to test the Brent-Dekker method :
 > 
 > #include <stdio.h>
 > #include <stdlib.h>
 > #include <gsl_roots.h>
 > 
 > static double a;
 > double fun (const double);
 > 
 > double fun (const double x) {
 >    return pow(x,5./2)-pow(x-2*a,5./2)-5*a/(2*sqrt(2.));
 > }
 > 
 > int main (void) {
 >    double *x;
 >    double *x0;
 >    double *x1;
 >    double rel_eps, abs_eps;
 >    unsigned int max_iter;
 >    int find;
 >    x0 = (double *) malloc (sizeof(double));
 >    x1 = (double *) malloc (sizeof(double));
 >    x = (double *) malloc (sizeof(double));
 >    *x0 = 0.3;
 >    *x1 = 1;
 >    x = NULL;
 >    rel_eps = 0.01;
 >    abs_eps = 0.001;
 >    max_iter = 50;
 >    a = 0.108;
 >    printf ("f(x0) = %f\n", fun(*x0));
 >    printf ("f(x1) = %f\n", fun(*x1));
 >    find = gsl_root_brent(x, fun, x0, x1, rel_eps, abs_eps, max_iter);
 >    if (find) printf ("Error : return = %d\n", find);
 >    printf ("x = %f\n", *x);
 >    exit (0);
 > }
 > 
 > gcc version egcs-2.91.66 19990314 (egcs-1.1.2 release) yields
 > gcc -ansi -pedantic -Werror -Wall -W -Wmissing-prototypes -Wstrict-prototypes -Wtraditional -Wconversion -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Waggregate-return -fshort-enums -fno-common -Wnested-externs -Dinline= -g -04   -c essai.c -o essai.ogcc: unrecognized option `-04'cc1: warnings being treated as errors
 > essai.c: In function `main':
 > essai.c:31: warning: passing arg 2 of `gsl_root_brent' from incompatible pointer typemake: *** [essai.o] Error 1
 > 
 > If i ignore the warning, at execution occurs a Memory fault (core dumped).
 > In the documentation i found
 > int gsl_root_brent (double *root, double (* f)(double),
 >                 double *lower_bound, double *upper_bound,
 >                 double rel_epsilon, double abs_epsilon,
 >                 unsigned int max_iterations);
 > 
 > but in the .h the prototype of the function is
 > int gsl_root_brent (double *root, const gsl_function * f,
 >                 double *lower_bound, double *upper_bound,
 >                 double rel_epsilon, double abs_epsilon,
 >                 unsigned int max_iterations);
 > struct gsl_function_struct
 > {
 >   double (* function) (double x, void * params);
 >   void * params;
 > };
 > typedef struct gsl_function_struct gsl_function ;
 > 
 > Can somebody help me to find the mistake ?
 > --
 > Rodolphe POLLET
 > Laboratoire de Chimie Theorique, Case 137,    |   pollet@lct.jussieu.fr
 > Universite Pierre et Marie Curie, T 22-23,    |   tel:   01.44.27.42.11
 > 4, Place Jussieu, 75252 PARIS CEDEX 05, FRANCE|   Fax :  44.27.41.17
 > 
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 > 
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 > raison..."
 > 
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