// Solves Jacobi Computation
// 
// Given an array A, iteratively replace its
// elements with the average of their four nearest
// neighbors, until the largest change between two
// consecutive iterations is less than delta. 
//
// Variable size version 
//

// Copyright by mpC team, 1999
//
//    http://www.ispras.ru/~cbr
//    mpc@ispras.ru

#define TYPE double

#define DELTA 0.0001
#define PREC 0.01

int reps;
int N;

void jacobi() {
  TYPE err;

  TYPE AA[N+2][N+2];
  TYPE T[N][N];
  
  reps=0;

  AA[]=0;
  AA[N+1][1:N]=1.0;

  do {
    reps++;
    
    T[]=0.25*( AA[0:N-1][1:N]+
               AA[2:N+1][1:N]+
               AA[1:N][0:N-1]+
               AA[1:N][2:N+1]
               );
    
    err=[+][+]((AA[1:N][1:N]-T[])*(AA[1:N][1:N]-T[]));
    AA[1:N][1:N]=T[];
  }
  while(err>DELTA);
}


void report() {
  printf("\nJacobi scheme used %d iterations.\n",
         reps);
}

main() {
  printf("Enter matrix size (N): ");
  scanf("%d",&N);
  jacobi();
  report();
}