#include "csi.h"

/* csi(S, S, D, D); */
void csi(int n, float x[MAX], float y[MAX], float z[MAX])
{
  float h[MAX],b[MAX],u[MAX],v[MAX];

  int i;

  for (i = 0; i<= n-1; i=i+1){
    h[i] = x[i+1]-x[i];
    b[i] = (6/h[i])*(y[i+1]-y[i]);
  }

  u[1] = 2*(h[0]+h[1]);
  v[1] = b[1]-b[0];
  for (i = 2; i <= n-1; i=i+1){
    u[i] = 2*(h[i]+h[i-1])-h[i-1]*h[i-1]/u[i-1];
    v[i] = b[i]-b[i-1]-h[i-1]*v[i-1]/u[i-1];
  }

  /* 
   * Workaround to replace 
   *   z[n] = 0;
   * until E&R parameters work
  {
    int t;
    t = n+1;
    z[t-1] = 0;
  }
   */

  z[n] = 0;

  i=n-1;
  if ( i>=1 )
    do {
      z[i] = (v[i]-h[i]*z[i+1])/u[i];
      i=i-1;
    } while ( i>=1 );
  z[0] = 0;
}