Re: [Help-gsl] Integration with C++

[GAUTAM DIVGI]

Hi,

Try this.  I have marked the changes. Since c routines do not have
information about the object on which to call the method any method in a
class that you wish to pass as a function pointer to a c++ method has to be
static.

class Testo
{
private:

   gsl_integration_workspace * w;
   gsl_function * pIntegrand;

public:
   Testo():
       w( gsl_integration_workspace
> _alloc(1000)),
>         pIntegrand( new gsl_function() )
>         {  ;};
>
> /********************/
> /* #(2) */
>
>     struct f_params{ double a; double b; };



       // -------------- change method to static
-----------------------------

>     static double f (double x, void * params) {
>         struct f_params * pList = (struct f_params *) params;
>         double a = (pList->a);
>         double b = (pList->b);
>
>
>         return a+b*x;
>
>     };
>
> /********************/
>
>     double Integrate()
>     {
>         double resIntegral, abserr;
>         struct f_params list= {0.0,1.0};
>
>         double x_start=0.0;
>         double x_end=1.0;
>         int limit=999;
>         double epsabs=0.0;
>         double epsrel=1e-6;


         //----------------- change from &f  -to- &(Testo::f)
----------------------------

       pIntegrand->function = &(Testo::f);
>         pIntegrand->params = &list;
>
>         gsl_integration_qag (pIntegrand, x_start, x_end, epsabs, epsrel,
> limit, 1,
>             w, &resIntegral, &abserr);
>
>         return resIntegral;
>     };
>
> };



---------- Forwarded message ----------
> From: "Ivan Liu" <address@hidden>
> To: address@hidden
> Date: Sun, 29 Oct 2006 17:29:45 +0100
> Subject: [Help-gsl] Integration with C++
> Hi,
>
> I would like to use the numerical integration routine in a C++ class
> environment, and I wrote the following test routine
>
>
> #include <iostream>
> #include <gsl/gsl_integration.h>
> using namespace std;
>
> /************************/
> // Integrand
>
> /* #(1)
>
> struct f_params{ double a; double b; };
>
> double f (double x, void * params) {
>     struct f_params * pList = (struct f_params *) params;
>     double a = (pList->a);
>     double b = (pList->b);
>
>
>     return a+b*x;
>
> };
> */
> /***************************/
>
> class Testo
> {
> private:
>
>     gsl_integration_workspace * w;
>     gsl_function * pIntegrand;
>
> public:
>     Testo():
>         w( gsl_integration_workspace_alloc(1000)),
>         pIntegrand( new gsl_function() )
>         {  ;};
>
> /********************/
> /* #(2) */
>
>     struct f_params{ double a; double b; };
>
>     double f (double x, void * params) {
>         struct f_params * pList = (struct f_params *) params;
>         double a = (pList->a);
>         double b = (pList->b);
>
>
>         return a+b*x;
>
>     };
>
> /********************/
>
>     double Integrate()
>     {
>         double resIntegral, abserr;
>         struct f_params list= {0.0,1.0};
>
>         double x_start=0.0;
>         double x_end=1.0;
>         int limit=999;
>         double epsabs=0.0;
>         double epsrel=1e-6;
>
>         pIntegrand->function = &f;
>         pIntegrand->params = &list;
>
>         gsl_integration_qag (pIntegrand, x_start, x_end, epsabs, epsrel,
> limit, 1,
>             w, &resIntegral, &abserr);
>
>         return resIntegral;
>     };
>
> };
>
>
>
>
> int main(void)
> {
>     Testo G;
>
>     cout <<  G.Integrate() << endl;
>
>     return 0;
> }
>
>
>
> The program doesn't compile and the message is:
>
> test.cpp: In member function 'double Testo::Integrate()':
> test.cpp:62: error: ISO C++ forbids taking the address of an unqualified
> or
> parenthesized non-static member function to form a pointer to member
> function.  Say '&Testo::f'
> test.cpp:62: error: cannot convert 'double (Testo::*)(double, void*)' to
> 'double (*)(double, void*)' in assignment
>
> If I comment out the section marked #(2) and use #(1) instead, the program
> works no problem,
> but I'd like to put the integrand into the class.
>
> How do I do that?
>
> thanks,
> Ivan Liu
>
>
>
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