Jacobi Method/*  Step 1: Perform Jacobi Iteration        */
/********************************************/
for(i=1;i<N-1;i++)
  {
  for(j=1;j<N-1;j++)
    {
      v[i][j] = .25*(u[i][j-1]+u[i][j+1]+u[i-1][j]+u[i+1][j]);
     }
   }

/*  Get ready for the next Jacobi update */
for(i=1;i<N-1;i++)
  {
  for(j=1;j<N-1;j++)
    {
      u[i][j] = v[i][j];
     }
   }
 
 
 

30-ouray% cc -O jac.c
31-ouray% time a.out

12.0111u 0.1571s 0:12 96%
 

Gauss Seidel Method

/*  Step 1: Perform Gauss Seidel Iteration        */
/********************************************/
for(i=1;i<N-1;i++)
  {
  for(j=1;j<N-1;j++)
    {
      u[i][j] = .25*(u[i][j-1]+u[i][j+1]+u[i-1][j]+u[i+1][j]);
     }
   }
 

32-ouray% cc -O gs.c
33-ouray% time a.out

106.3182u 1.3910s 1:59 90%
34-ouray%