GSL Incorrect values with numerical Integration -

i have integrand 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 1 in class called veffclass.

my integration routine be

long double veffclass::numintinf(long double low, double sign, long double masssquared, long double temp) { //long double  res = 0; double = 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;  } 

with c_threshold = 1e-3;

if run numintinf(10^-3, +1 , 100, 500) result 1.83038. result given maple ~ 6*10^9 . if use simple simpsons 1/3 method differes 1% maple result.

can point me error?

thanks suggestions

whenever ask question involves numerical results (and bugs) need provide concise code can analyze , run reproduce original problem. yes, information missing. need

(1) concise code (we don't need veffclass!) gsl integration (you partially provided - code still quite complicated stack overflow purposes).

(2) concise code implementation of simpson-rule.

(3) snapshot of maple calculation.

(2) , (3) quite important because question arises due fact methods (2) , (3) disagree (1), assumed incorrect answer. why did assume (1) incorrect , not other way around? have analytical solution check numbers?

when analyzed, in wolfram mathematica, integrand parameters values provided in comment, got answer consistent gsl calculation. can't reproduce problem , without (2) + (3) can guess went wrong...

i attached snapshot of mathematica notebook.