Re: [Help-gsl] Error in integration

[Carsten Fortmann]

VINU,
consider this:

double fw(double x, void * params=&gAlpha)
{
        gsl_error_handler_t * old_handler=gsl_set_error_handler_off();
//switch off default error handler, store old error handler in
//old_handler
        
        gsl_integration_workspace * workspace=
gsl_integration_workspace_alloc(10000);

        gsl_function F;
        F.function=&A;  //double A() is declared elsewhere in the code
        F.params=&gAlpha;

        double LoLimit=-1.;
        double UpLimit=1.;
        double relerr=0.01;   //initial error tolerance (relative error)
        int status=1;
        while(status)
        {
        status=gsl_integration_qag(&F,LoLimit,
UpLimit,0.,relerr,10000,1,workspace,&result1,&error);
        relerr*=1.1;
        if(status) std::cout<<"Increased tolerance="<<relerr<<"\n";
        }
//if integration routine returns error code, integration is repeated
//using increased error tolerance, message is printed out
        
        gsl_set_error_handler(old_handler); //reset error handler (might
be unneccessary.
        return result1;
}



VINU V. wrote:
> dear sir
> I am doing integration using gsl.
> But for some parameters in the function to be integrated, i am 
getting the
> error
> "gsl: qags.c:548: ERROR: cannot reach tolerance because of roundoff error
> Default GSL error handler invoked.
> error: line 4:  2251 Aborted                 (core dumped) ./a.out"
> I have to do the integration for a huge set of parameters. I need to
> neglect those parameters and continue the integration for the next set of
> parameters.
> I don't know how to use the error handler for integration.
>
> Could you please help me?
> regards
> Vinu Vikram

--


*********************************************
Carsten Fortmann
Inst. f. Physik
Universitaet Rostock
18051 Rostock

Tel: +49-381-498-6943
Fax: +49-381-498-6942
mailto address@hidden
http://www.mpg.uni-rostock.de/mp
*********************************************


--


*********************************************
Carsten Fortmann
Inst. f. Physik
Universitaet Rostock
18051 Rostock

Tel: +49-381-498-6943
Fax: +49-381-498-6942
mailto address@hidden
http://www.mpg.uni-rostock.de/mp
*********************************************