<![CDATA[
#include <stdio.h>
#include <math.h>
#define NPT 100
#define SPREAD 0.1
#define NTERM 4
void funcs(double x, double func[]) {
func[0]=cos(x);
func[1]=sin(x);
func[2]=exp(x);
func[3]=1.0;
}
int main(void) {
int i,j;
array int ia[NTERM];
array double a[NTERM],x[NPT],y[NPT],sig[NPT],covar[NTERM][NTERM],u[NPT];
double chisq;
linspace(x, 0, 10);
urand(u);
y = 4*cos(x) + 3*sin(x) +2*exp(x) +(array double [NPT])1.0 + SPREAD*u;
sig=(array double[NPT])(SPREAD);
ia[0] = 0; ia[1] = 1; ia[2] = 0; ia[3] = 1;
a[0] = 4; a[1] = 3; a[2] = 2; a[3] = 1;
curvefit(a,x,y,funcs,sig,ia,covar,&chisq);
printf("\n%11s %21s\n","parameter","uncertainty");
for (i=0;i<NTERM;i++)
printf(" a[%1d] = %8.6f %12.6f\n",i,a[i],sqrt(covar[i][i]));
printf("chi-square = %12f\n",chisq);
printf("full covariance matrix\n");
printf("%12f",covar);
}
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parameter uncertainty
a[0] = 4.000000 0.000000
a[1] = 2.994009 0.015044
a[2] = 2.000000 0.000000
a[3] = 1.052622 0.010357
chi-square = 7.537645
full covariance matrix
0.000000 0.000000 0.000000 0.000000
0.000000 0.000226 0.000000 -0.000041
0.000000 0.000000 0.000000 0.000000
0.000000 -0.000041 0.000000 0.000107