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Re: [Help-gsl] Numerical integration QAGS cannot reach tolerance and abo


From: Juan Pablo Amorocho
Subject: Re: [Help-gsl] Numerical integration QAGS cannot reach tolerance and aborts
Date: Sun, 5 Oct 2014 08:53:35 +0200

HI all, 
I evaluated the function on the integration, and didn’t see anything 
suspicious. Though one thing caught my eye. Vipin, you are passing  a relative 
error of 10e-12. Have you tried a value of 10e-6 or 10e-7? By the way, what’s 
is the value of n and what does int n(1) resolves to? In the code below I 
assume n = 1.  I don’t mean to be picky, but could you please send us (or me)  
code that we could “just” copy& paste without further modification in order to 
compile and run? Thanks!

— Juan Pablo

#include <stdio.h>
#include <math.h>


double f (double x){
const double a = 0.992*M_PI/2;
const double n = 1.0;
return cos(n*x)*log((cos(a) - cos(x))/(x - a));

}

int main(){

double a = 0.0;
double h = 0.01;
double fa = 0.;
do{
fa = f(a);
printf("(%f, %f)\n", a, fa);
a+=h;
}while(a <=M_PI);

return 0;

}

On 04 Oct 2014, at 19:08, Klaus Huthmacher <address@hidden> wrote:

> Dear Vipin,
> 
>> //  double f = cos(n*x)*log((cos(a) - cos(x))/(x - a));//
> 
> Is it possible that the argument of your logarithm can be zero for PI? Or
> that you divide by zero, if x-a becomes zero for PI?
> 
> Kind regards,
>  Klaus.
> 
> 



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