/**************************************************************************** * DESCRIPTION: * Serial HEAT2D Example - C Version * This example is based on a simplified * two-dimensional heat equation domain decomposition. The initial * temperature is computed to be high in the middle of the domain and * zero at the boundaries. The boundaries are held at zero throughout * the simulation. During the time-stepping, an array containing two * domains is used; these domains alternate between old data and new data. * * The physical region, and the boundary conditions, are suggested by this diagram; u = 0 +------------------+ | | u = 100 | | u = 100 | | | | | | | | +------------------+ u = 100 Interrior point : u[Central] = (1/4) * ( u[North] + u[South] + u[East] + u[West] ) PARALLEL MPI VERSION : +-------------------+ | | P0 m=(n-2)/P +2 +-------------------+ | | P1 +-------------------+ n | | .. +-------------------+ | | Pq +-------------------+ <-------- n --------> <-------n-2 ------> ****************************************************************************/ #include #include #include #include #define NN 50 #define MM 50 #define RING 100 #define ITER_PRINT 100 #define PRINT_DATA 1 #define MAX_ITER 1000 #define _EPSILON 0.01 float update(int rank,int size, int nx,int ny, float *u, float *unew); void inidat(int rank, int size, int nx, int ny, float *u, float *unew); void prtdat(int rank, int size, int nx, int ny, float *u,const char *fnam); int main(int argc, char *argv[]) { int N=NN,M=MM; int rank,size; float EPSILON=_EPSILON; /* INITIALIZE MPI */ MPI_Init(&argc, &argv); /* GET THE PROCESSOR ID AND NUMBER OF PROCESSORS */ MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Comm_size(MPI_COMM_WORLD, &size); //Only Rank 0 read application parameters if(rank==0) { if(argc !=3) { fprintf(stderr,"usage %s N EPSILON\n ", argv[0]); fprintf(stderr,"\t\twhere N is GRID size, EPSILON is Tolerance\n"); fprintf(stderr,"\t\texample N = 100, EPSILON = 0.1\n"); return -1; } N = M = atoi(argv[1]); EPSILON = atof(argv[2]); if(N % size!=0) { fprintf(stderr,"Grid Size MUST be divisible by the number of processors !"); return -1; } } //Wait for rank 0 , all process start here MPI_Barrier(MPI_COMM_WORLD); //Exchange N MPI_Bcast(&N , 1, MPI_FLOAT, 0 , MPI_COMM_WORLD); //Exchange EPSILON MPI_Bcast(&EPSILON , 1, MPI_FLOAT, 0 , MPI_COMM_WORLD); //local size M = (N-2)/size + 2; float *u = (float *)malloc(N * M * sizeof(float)); float *unew = (float *)malloc(N * M * sizeof(float)); if(u==0 || unew ==0) { perror("Can't allocated data\n"); return -1; } if(rank==0) { printf ( "\n" ); printf ( "HEATED_PLATE\n" ); printf ( " Parallel MPI version using %d processors \n",size ); printf ( " A program to solve for the steady state temperature distribution\n" ); printf ( " over a rectangular plate.\n" ); printf ( "\n" ); printf ( " Spatial grid of %d by %d points.\n", N, N ); printf ( " Each processor will use grid of %d +2 by %d points.\n", M-2, N ); printf ( " The iteration will end until tolerance <= %f\n\n",EPSILON); } /* Initialize grid and create input file * each process initialize its part * */ inidat(rank,size,M,N,u,unew); prtdat(rank,size,M,N,u, "initial.dat"); /* * iterate until the new solution unew differs from the old solution u * by no more than EPSILON. * */ float diff=1.0; int iter=0; while(diff> EPSILON) { diff= update(rank,size,M,N, u, unew); if(rank==0) if(iter%ITER_PRINT==0) printf("Processor #%d, iteration %d, epsilon = %f\n ", rank,iter,diff); iter++; } prtdat(rank,size,M,N, u, "final.dat"); free(u); free(unew); MPI_Finalize(); } /**************************************************************************** * subroutine update ****************************************************************************/ float update(int rank, int size, int nx,int ny, float *u, float *unew){ int ix, iy; float diff=0.0; float globaldiff; MPI_Status status; /* * EXCHANGE GHOST CELL */ if (rank > 0 && rank< size-1) { MPI_Sendrecv(&u[ny*(nx-2)], ny, MPI_FLOAT, rank+1, 0, &u[ny*0], ny, MPI_FLOAT, rank-1, 0, MPI_COMM_WORLD, &status); MPI_Sendrecv(&u[ny*1], ny, MPI_FLOAT, rank-1, 1, &u[ny*(nx-1)], ny, MPI_FLOAT, rank+1, 1, MPI_COMM_WORLD, &status); } else if (rank == 0 && rank< size-1) MPI_Sendrecv(&u[ny*(nx-2)], ny, MPI_FLOAT, rank+1, 0, &u[ny*(nx-1)], ny, MPI_FLOAT, rank+1, 1, MPI_COMM_WORLD, &status); else if ( rank> 0 && rank == size-1) MPI_Sendrecv(&u[ny*1], ny, MPI_FLOAT, rank-1, 1, &u[ny*0], ny, MPI_FLOAT, rank-1, 0, MPI_COMM_WORLD, &status); /** * PERFORM LOCAL COMPUTATION * */ for (ix = 1; ix < nx-1; ix++) { for (iy = 1; iy < ny-1; iy++) { unew[ix*ny+iy] = (u[(ix+1)*ny+iy] + u[(ix-1)*ny+iy] + u[ix*ny+iy+1] + u[ix*ny+iy-1] )/4.0 ; if (diff < fabs (unew[ix*ny+iy] - u[ix*ny+iy] )) { diff = fabs ( unew[ix*ny+iy] - u[ix*ny+iy] ); } } } /** * COMPUTE GLOBAL CONVERGENCE * * */ MPI_Allreduce(&diff, &globaldiff , 1, MPI_FLOAT, MPI_MAX, MPI_COMM_WORLD); /** * COPY OLD DATA * */ for (ix = 1; ix < nx-1; ix++) { for (iy = 1; iy < ny-1; iy++) { u[ix*ny+iy] = unew[ix*ny+iy]; } } return globaldiff; } /***************************************************************************** * Initialize Data *****************************************************************************/ void inidat(int rank, int size,int nx, int ny, float *u, float *unew) { int ix, iy; /* *Set boundary data and interrior values * */ // interior points for (ix = 1; ix < nx-1; ix++) for (iy = 1; iy < ny-1; iy++) { u[ix*ny+iy]=0.0; } //boundary left for (ix = 1; ix < nx-1; ix++){ u[ix*ny]=100.0; } //boundary right for (ix = 1; ix < nx-1; ix++){ u[ix*ny+ (ny-1)]=100.0; } //boundary down for (iy = 0; iy < ny; iy++){ if(rank==size-1) { u[(nx-1)*(ny)+iy]=100.0; }else { u[(nx-1)*(ny)+iy]=0.0; } } //boundary top for (iy = 0; iy < ny; iy++){ u[iy]=0.0; } } /*************************************************************************** * Print Data to files **************************************************************************/ void print2file(int rank, int nx, int ny, float *u,const char *fname) { int ix, iy; FILE *fp; char str[255]; sprintf(str, "%d_%s", rank,fname); fp = fopen(str, "w"); for (ix = 0 ; ix < nx; ix++) { for (iy =0; iy < ny; iy++) { fprintf(fp, "%6.2f ", u[ix*ny+iy]); } fputc ( '\n', fp); } fclose(fp); } void prtdat(int rank, int size,int nx, int ny, float *u,const char *fname) { if(ITER_PRINT==0)return; /** * USE TOKEN RING to write to unique file * 0 will rite first and then 1, 2, ... size-1 * * * */ print2file(rank,nx,ny,u,fname); }