Re: [Help-gsl] calling a gsl_function from a structure of functions

[Benjamin Blumer]

It shouldn't be a problem.  gsl_function, which is defined in 
gsl_math.h, is a structure containing a pointer to a function that takes 
a double, and a pointer to a structure that contains the parameters.  
Structures are allowed to contain pointers to functions - although not 
functions themselves.

I chopped an example out of something I've been working on:

    #include <stdio.h>
    #include <stdlib.h>
    #include <gsl/gsl_math.h>

    typedef struct
    {
        double Constant;
    } parameters;


    typedef struct
    {
        gsl_function addConstant;
        gsl_function subtractConstant;
    } structureOfFunctions;

    double function1 (double x, void * params)
    {
        parameters * f1params = (parameters*) params;
        double C = (f1params->Constant);
        return x + C;
    }
    double function2 (double x, void * params)
    {

        parameters * f2params = (parameters*) params;
        double C = (f2params->Constant);
        return x - C;
    }



    int main()
    {
        structureOfFunctions firstGroupOfFunctions;

        parameters first = {5};
        firstGroupOfFunctions.addConstant.function = &function1;
        firstGroupOfFunctions.addConstant.params = &first;

        parameters second = {2};
        firstGroupOfFunctions.subtractConstant.function = &function2;
        firstGroupOfFunctions.subtractConstant.params = &second;

        printf("\n%lf", GSL_FN_EVAL(&firstGroupOfFunctions.addConstant, 
10));
        printf("\n%lf", 
GSL_FN_EVAL(&firstGroupOfFunctions.subtractConstant, 10));
        printf("\n");
        return 0;
    }


On 11-08-02 01:19 PM, Laura Florescu wrote:
> Hi, I have a structure
> field_integrand fld_integrand(double kz, void *p) in which I am
> computing a few functions and returning them in a structure. Then I
> want to integrate those functions so I have a function field
> fld(double r, double z) in which I'd like to integrate those
> functions, and it hasn't really worked out to declare them in this fld
> function.
>
> Does anybody know if I can declare gsl_functions from a structure of functions?
>
> Thanks a lot,
> Laura
>
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