void dqag0(double (*f)(double), double a, double b, double epsabs, double epsrel, double *result, double *abserr, double *work, long int lwork, long int *iwork, long int liwork, int *ifail)
{
//
// based on quadpack routine
//
// dqag0 is a general purpose integrator which calculates
// an approximation to the integral of a function over a finite
// interval (a,b)
//
// dqag0 itself is essentially a dummy routine whose function is to
// partition the work arrays work and iwork for use by dqags.
// work is partitioned into 4 arrays each of size lwork/4.
// iwork is a single array in dqags.
//
// .. scalar arguments ..
int ibl, iel, ier, irl, limit;
// .. subroutine references ..
// dqags
// ..
// check that minimum workspace requirements are met
if (lwork<4)
{
ier = 6;
*ifail = 1;
return;
}
if (liwork<lwork/8+2)
{
ier = 6;
*ifail = 1;
return;
}
// limit = upper bound on number of subintervals
limit = lwork/4;
// set up base addresses for work arrays
ibl = limit + 1;
iel = limit + ibl;
irl = limit + iel;
// perform integration
dqags(f, a, b, fabs(epsabs), fabs(epsrel), &(work[1]),&(work[ibl]), &(work[iel]), &(work[irl]), limit, iwork, liwork, result, abserr, &ier);
if (ier!=0) {*ifail = 1;}
else {*ifail = 0;}
return;
}//dqag0
int main()
{
double a,b,epsabs,epsrel,abserr;
double resabs,resasc;
double y;
int neval,ier;
a = 0.0;
b = 1.0;
epsabs = 0.0;
epsrel = 1e-3;
y=dqags(efunc,a,b,epsabs,epsrel,&abserr,&neval,&ier,0);
printf("dqags integral = %.17lg\n",y);
printf("abserr = %.17lg, neval = %d, ier = %d\n",
abserr,neval,ier);
return 0;
}
double Iinv( Lgm_MagModelInfo *mInfo ) {
double a, b;
double epsabs, epsrel, result, abserr;
double resabs, resasc;
int key, neval, ier, limit, lenw, last, iwork[501];
double work[2002];
_qpInfo *qpInfo;
/*
* Type-cast our data structure to a generic type.
* The structure holds auzilliary info we need down
* in the function calls.
*/
qpInfo = (_qpInfo *)mInfo;
/*
* Limits of integration.
*/
a = mInfo->Sm_South;
b = mInfo->Sm_North;
/*
* set tolerances.
*/
//epsabs = mInfo->epsabs;
//epsrel = mInfo->epsrel;
epsabs = mInfo->Lgm_I_Integrator_epsabs;
epsrel = mInfo->Lgm_I_Integrator_epsrel;
/*
* Init some vars used in I_integrand() (these are not declared static in
* I_integrand() in order to avoid making it non-reentrant).
*/
mInfo->Lgm_I_integrand_S = 0.0;
mInfo->Lgm_I_integrand_FirstCall = TRUE;
mInfo->Lgm_n_I_integrand_Calls = 0;
if ( mInfo->Lgm_I_Integrator == DQAGS ) {
/*
* Use DQAGS
*/
limit = 500; lenw = 4*limit; key = 6;
dqags(I_integrand, qpInfo, a, b, epsabs, epsrel, &result, &abserr, &neval, &ier, limit, lenw, &last, iwork, work, mInfo->VerbosityLevel );
} else if ( mInfo->Lgm_I_Integrator == DQK21 ) {
/*
* Use DQK21
*/
dqk21(I_integrand, qpInfo, a, b, &result, &abserr, &resabs, &resasc);
} else {
/*
* Unknown Integrator
*/
printf("Iinv: Unknown integrator. Lgm_Inv_Integrator = %d\n", mInfo->Lgm_n_I_integrand_Calls );
result = -9e99;
}
return( result );
}