laplace2d_v2.cpp

/* Copyright (c) 2012, NVIDIA CORPORATION. All rights reserved.
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 #include <math.h>
 #include <string.h>
 #include <stdlib.h>
 #include <omp.h>
 #include <stdio.h>
 #include <mpi.h>
 #include <mpi_navier.h>

 #define UP    0
 #define DOWN  1
 #define LEFT  2
 #define RIGHT 3
 
 int main(int argc, char** argv)
 {
     
     //Size along y
     int jmax = 4094;
     //Size along x
     int imax = 4094;

     //TODO initialize MPI
     
     MPI_Init(&argc,&argv);
     mpi_setup(&imax, &jmax);
    


     int iter_max = 1000;
     
     const double pi  = 2.0 * asin(1.0);
     const double tol = 1.0e-5;
     double error     = 1.0;
 
     double *A;
     double *Anew;
     double *y0;
 
     A    = (double *)malloc((imax+2) * (jmax+2) * sizeof(double));
     Anew = (double *)malloc((imax+2) * (jmax+2) * sizeof(double));
     y0   = (double *)malloc((jmax+2) * sizeof(double));
 
     memset(A, 0, (imax+2) * (jmax+2) * sizeof(double));
     
     // set boundary conditions
     //TODO: this loop should only done by processes who have no previous neighbour in the y direction (no up neighbour)
     if(prev_y == MPI_PROC_NULL){
        for (int i = 0; i < imax+2; i++)
            A[(0)*(imax+2)+i]   = 0.0;
     }
     
 
     //TODO: this loop should only done by processes who have no next neighbour in the y direction (no down neighbour)
     if(next_y == MPI_PROC_NULL){
        for (int i = 0; i < imax+2; i++)
           A[(jmax+1)*(imax+2)+i] = 0.0;

     }
     
     //TODO: this loop should only done by processes who have no previous neighbour in the x direction (no left neighbour)
     if(prev_x == MPI_PROC_NULL){
     for (int j = 0; j < jmax+2; j++)
         {
             y0[j] = sin(pi * (j+gbl_j_begin) / (jmax_full+1)); //TODO: within sin(), j is a global index and jmax is the global size
                                           //need to offset j by the beginning j index of this partition, and use the full jmax size
            A[(j)*(imax+2)+0] = y0[j];
        } 
 
     }
     
     //TODO: this loop should only done by processes who have no next neighbour in the x direction (no right neighbour)
     if(next_x == MPI_PROC_NULL){
        for (int j = 0; j < imax+2; j++)
        {
            y0[j] = sin(pi * (j*gbl_j_begin)/ (jmax_full +1)); //TODO: within sin(), j is a global index and jmax is the global size
                                            //need to offset j by the beginning j index of this partition, and use the full jmax size
            A[(j)*(imax+2)+imax+1] = y0[j]*exp(-pi);
        }
    }
     //TODO: Need to set A to dirty
 
     //TODO: Only process 0 should print this, and with the full imax and jmax sizes
     if (my_rank == 0)
     printf("Jacobi r elaxation Calculation: %d x %d mesh\n", imax_full+2, jmax_full+2);
     
     double t1 = omp_get_wtime();
     int iter = 0;
     
     //TODO: this loop should only done by processes who have no previous neighbour in the y direction
     if(prev_y == MPI_PROC_NULL)
     for (int i = 1; i < imax+2; i++)
        Anew[(0)*(imax+2)+i]   = 0.0;
 
     //TODO: this loop should only done by processes who have no next neighbour in the y direction
     if(next_y == MPI_PROC_NULL)
     for (int i = 1; i < imax+2; i++)
        Anew[(jmax+1)*(imax+2)+i] = 0.0;
 
     //TODO: this loop should only done by processes who have no previous neighbour in the x direction
     if(prev_x == MPI_PROC_NULL)
     for (int j = 1; j < jmax+2; j++)
         Anew[(j)*(imax+2)+0]   = y0[j];
 
     //TODO: this loop should only done by processes who have no next neighbour in the x direction
     if(next_x == MPI_PROC_NULL)
     for (int j = 1; j < jmax+2; j++)
         Anew[(j)*(imax+2)+imax+1] = y0[j]*expf(-pi);
     
     //TODO: Need to set Anew to dirty
 
     while ( error > tol && iter < iter_max )
     {
         error = 0.0;
         //TODO: need to make sure stencil accesses to A read correct data
         exchange_halo(imax,jmax,A);
 #pragma omp parallel for reduction(max:error)
         for( int j = 1; j < jmax+1; j++ )
         {
             for( int i = 1; i < imax+1; i++)
             {
                 Anew[(j)*(imax+2)+i] = 0.25f * ( A[(j)*(imax+2)+i+1] + A[(j)*(imax+2)+i-1]
                                      + A[(j-1)*(imax+2)+i] + A[(j+1)*(imax+2)+i]);
                 error = fmax( error, fabs(Anew[(j)*(imax+2)+i]-A[(j)*(imax+2)+i]));
             }
         }
         //TODO: need global reduction for error
         double error_global = 0;
         MPI_Allreduce(&error, &error_global, 1, MPI_DOUBLE, MPI_MAX, MPI_COMM_WORLD);
         error = error_global;

         //No stencil accesses to Anew, no halo exchange necessary
         for( int j = 1; j < jmax+1; j++ )
         {
             for( int i = 1; i < imax+1; i++)
             {
                 A[(j)*(imax+2)+i] = Anew[(j)*(imax+2)+i];    
             }
         }
         //TODO: Only process 0 should print this

         if(iter % 100 == 0 && my_rank == 0) printf("%5d, %0.6f\n", iter, error);
         
         iter++;
     }
 
     double runtime = omp_get_wtime()-t1;
  
     printf(" total: %f s\n", runtime);
        
     
     //TODO finalize MPI
     MPI_Finalize();
     return 0;
 }