/*************************    Program 6.2    ****************************/
/*                                                                      */
/************************************************************************/
/* Please Note:                                                         */
/*                                                                      */
/* (1) This computer program is written by Tao Pang in conjunction with */
/*     his book, "An Introduction to Computational Physics," published  */
/*     by Cambridge University Press in 1997.                           */
/*                                                                      */
/* (2) No warranties, express or implied, are made for this program.    */
/*                                                                      */
/************************************************************************/

#include <stdio.h>
#include <math.h>

void rxln (fn,dn,s,n,p,h)
/* Subroutine performing one iteration of Relaxation for the
   one-dimensional stationary diffusion equation. DN is the
   diffusion coefficient shifted half step towards x=0.
   Copyright (c) Tao Pang 1997. */
int n; 
double p,h;
double fn[],dn[],s[];
{
int i;
double h2,q;

h2 = h*h;
q  = 1-p;

for (i = 1; i < n-1; ++i)
  {
  fn[i] = q*fn[i]+p*(dn[i+1]*fn[i+1]+dn[i]*fn[i-1]+h2*s[i])/(dn[i+1]+dn[i]);
  }
}