Page MenuHomec4science
Files F97918163

spline.c
No OneTemporary
Actions

File Metadata

Created
Tue, Jan 7, 13:31

spline.c
View Options

#include <stdlib.h>
/* Global variables used :
* - none
*/
void spline(const double *x, const double *y, int n, double yp1, double ypn, double *y2)
{
int i, k;
double p, qn, sig, un, *u;
u = (double *) malloc(n * sizeof(double));
if (yp1 > 0.99e30)
y2[0] = u[0] = 0.0;
else
{
y2[0] = -0.5;
u[0] = (3.0 / (x[1] - x[0])) * ((y[1] - y[0]) / (x[1] - x[0]) - yp1);
}
for (i = 1; i < n - 1; i++)
{
sig = (x[i] - x[i-1]) / (x[i+1] - x[i-1]);
p = sig * y2[i-1] + 2.0;
y2[i] = (sig - 1.0) / p;
u[i] = (y[i+1] - y[i]) / (x[i+1] - x[i]) - (y[i] - y[i-1]) / (x[i] - x[i-1]);
u[i] = (6.0 * u[i] / (x[i+1] - x[i-1]) - sig * u[i-1]) / p;
}
if (ypn > 0.99e30)
qn = un = 0.0;
else
{
qn = 0.5;
un = (3.0 / (x[n-1] - x[n-2])) * (ypn - (y[n-1] - y[n-2]) / (x[n-1] - x[n-2]));
}
y2[n] = (un - qn * u[n-1]) / (qn * y2[n-1] + 1.0);
for (k = n - 1; k >= 1; k--)
y2[k] = y2[k] * y2[k+1] + u[k];
free(u);
}

Event Timeline

c4science · Help