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#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_bspline.h>
#include <gsl/gsl_rng.h>
#include <gsl/gsl_randist.h>
#include <gsl/gsl_statistics.h>
int
main (void)
{
const size_t n = 500; /* number of data points to fit */
const double a = 0.0; /* data interval [a,b] */
const double b = 15.0;
const size_t max_spline_order = 5; /* maximum spline order */
const size_t nbreak = 10; /* number of breakpoints */
const double sigma = 0.2; /* noise */
gsl_bspline_workspace **work = malloc(max_spline_order * sizeof(gsl_bspline_workspace *));
gsl_vector **c = malloc(max_spline_order * sizeof(gsl_vector *));
gsl_vector *x = gsl_vector_alloc(n);
gsl_vector *y = gsl_vector_alloc(n);
gsl_vector *w = gsl_vector_alloc(n);
size_t i;
gsl_rng *r;
double chisq;
gsl_rng_env_setup();
r = gsl_rng_alloc(gsl_rng_default);
/* this is the data to be fitted */
for (i = 0; i < n; ++i)
{
double xi = (b - a) / (n - 1.0) * i + a;
double yi = cos(xi) * exp(-0.1 * xi);
double dyi = gsl_ran_gaussian(r, sigma);
yi += dyi;
gsl_vector_set(x, i, xi);
gsl_vector_set(y, i, yi);
gsl_vector_set(w, i, 1.0 / (sigma * sigma));
printf("%f %f\n", xi, yi);
}
printf("\n\n");
for (i = 0; i < max_spline_order; ++i)
{
/* allocate workspace for this spline order */
work[i] = gsl_bspline_alloc(i + 1, nbreak);
c[i] = gsl_vector_alloc(gsl_bspline_ncontrol(work[i]));
/* use uniform breakpoints on [a, b] */
gsl_bspline_init_uniform(a, b, work[i]);
/* solve least squares problem */
gsl_bspline_wlssolve(x, y, w, c[i], &chisq, work[i]);
}
/* output the spline curves */
{
double xi;
for (xi = a; xi <= b; xi += 0.1)
{
printf("%f ", xi);
for (i = 0; i < max_spline_order; ++i)
{
double result;
gsl_bspline_calc(xi, c[i], &result, work[i]);
printf("%f ", result);
}
printf("\n");
}
}
for (i = 0; i < max_spline_order; ++i)
{
gsl_vector_free(c[i]);
gsl_bspline_free(work[i]);
}
gsl_rng_free(r);
gsl_vector_free(x);
gsl_vector_free(y);
gsl_vector_free(w);
free(work);
free(c);
return 0;
}
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