65 lines
1.5 KiB
C
65 lines
1.5 KiB
C
#include <stdio.h>
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#include <math.h>
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#include <gsl/gsl_integration.h>
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#include <gsl/gsl_errno.h>
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#ifndef EPSABS
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#define EPSABS 0
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#endif
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#ifndef EPSREL
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#define EPSREL 1e-8
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#endif
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#ifndef LIMIT
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#define LIMIT 8192 //???
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#endif
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#ifndef R0
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#define R0 8e-6
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#endif
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/* Relevant quadrature methods from gsl:
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* gsl_integration_qagiu
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* ... and that's probably it.
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*/
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//gsl_function sigma2_integrand;
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struct sigma2_integrand_params {
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int n;
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double k, R;
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};
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static inline double sq(double x) {return x * x;}
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double sigma2_integrand(double ksi, void *params) {
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struct sigma2_integrand_params *p = (struct sigma2_integrand_params *) params;
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return exp(-sq(p->R*ksi) + sq(p->k/ksi/2)) * pow(ksi, 2*p->n);
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}
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int main(int argc, char **argv) {
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struct sigma2_integrand_params p;
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gsl_function F;
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F.function = sigma2_integrand;
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F.params = &p;
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gsl_integration_workspace *workspace = gsl_integration_workspace_alloc(LIMIT);
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gsl_error_handler_t * old_handler=gsl_set_error_handler_off();
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double eta, eta_orig, k_orig, R_orig;
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while (scanf("%d %lf %lf %lf", &(p.n), &k_orig, &R_orig, &eta_orig) == 4) {
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eta = eta_orig * R0;
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p.k = k_orig * R0;
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p.R = R_orig / R0;
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double result, abserr;
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int retval = gsl_integration_qagiu(&F, eta, EPSABS, EPSREL,
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LIMIT, workspace, &result, &abserr);
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double normfac = pow(R0, -2*p.n - 1);
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result *= normfac;
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abserr *= normfac;
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printf("%d %.16g %.16g %.16g %.16g %.16g %d\n", p.n, k_orig, R_orig,
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eta_orig, result, abserr, retval);
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}
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gsl_integration_workspace_free(workspace);
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}
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