[Help-gsl] Incorrect values with Integration

[Philipp Basler]

Hello,

I have an Integrand which reads

static double Integrand(double k , void * params)
    {
     long double *p = (long double *)params;
      long double MassSquared = p[0];
      long double Temp = p[1];
      long double sign = p[2];

      long double EXP = std::exp(-std::sqrt(k*k+MassSquared/(Temp*Temp)));
      double res = 0;
      if(sign == -1)
      {
        res = k*k*std::log(1-exp(-std::sqrt(k*k+MassSquared/(Temp*Temp))));
      }
      else if(sign == +1)
      {
        res = k*k*std::log(1+exp(-std::sqrt(k*k+MassSquared/(Temp*Temp))));
      }
      return res;
    };

This one is in a Class called VEffClass.

My Integration Routine would then be

long double VEffClass::NumIntInf(long double low, double sign, long double
MassSquared, long double Temp)
{
 //long double  res = 0;
  double up =
std::sqrt(std::log(C_threshold)*std::log(C_threshold)-MassSquared/(Temp*Temp));
 long double StepSize = (up-low)/C_IntSteps;
 long double par[3] = {MassSquared, Temp, sign};


 if(Temp == 0) return 0;

 gsl_integration_workspace *w = gsl_integration_workspace_alloc(5e+5);
 double result, error;
 gsl_function F;
 F.function = &VEffClass::Integrand;
 F.params = ∥

 gsl_integration_qags(&F, C_threshold, up, 1e-07, 0, 5e+5, w, &result,
&error);
 gsl_integration_workspace_free(w);

 return result;

}

C_threshold = 1e-3;

If I run NumIntInf(10^-3, +1 , 100, 500) the result is 1.83038. The Result
given by Maple is ~ 6*10^9 . If I use a simple Simpsons 1/3 Method it
differes about 1% from the Maple result.

Can anyone point me to the Error?

Best regards,
Philipp Basler.