spline.c
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	#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);
	}