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Gauss_seidel_redblack.c
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#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include "mpi.h"
#include "Checks.h"
void Gauss_seidel_redblack(double ***f,double *** u, int n, int N,int max_iter,double * tolerance) {
int size, rank;
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
//Initialize Constants
double FrobNorm = 10; //accumilator for frobenius norm
int iter = 0; //iterator
double u_tmp;
double delta_sq = 4.0/(N*N);
double h = 1.0/6;
int i,j,k;
double tolCheck = (*tolerance)*(*tolerance);
int FrobCheckFreq = 100;
//Neighbor
int neigh[4];
NeighbourCheck(neigh, size, rank);
// Make stride information
MPI_Datatype send;
// n-2 antal blocks - N-2 antal af elementer pr block - N*n antal elementer imellem hver block
MPI_Type_vector(n-2,N-2,N*n,MPI_DOUBLE,&send);
MPI_Type_commit(&send);
// Initialize requests as null
int noRequests = 8;
MPI_Request requests[noRequests];
for(int i = 0; i < noRequests; i++){
requests[i] = MPI_REQUEST_NULL;
}
if (neigh[0] != -1){
// send and recieve above
MPI_Irecv(&(u[1][0][1]), 1, send, neigh[0], max_iter+2, MPI_COMM_WORLD,&requests[0]);
MPI_Isend(&(u[1][1][1]), 1, send, neigh[0], max_iter+2, MPI_COMM_WORLD,&requests[1]);
}
if (neigh[1] != -1){
// send and recieve left
MPI_Irecv(&(u[0][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], max_iter+2, MPI_COMM_WORLD,&requests[2]);
MPI_Isend(&(u[1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], max_iter+2, MPI_COMM_WORLD,&requests[3]);
}
if (neigh[2] != -1){
// send and recieve right
MPI_Irecv(&(u[n-1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], max_iter+2, MPI_COMM_WORLD, &requests[4]);
MPI_Isend(&(u[n-2][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], max_iter+2, MPI_COMM_WORLD, &requests[5]);
}
if (neigh[3] != -1){
// send and recieve below
MPI_Irecv(&(u[1][n-1][1]), 1, send, neigh[3], max_iter+2, MPI_COMM_WORLD,&requests[6]);
MPI_Isend(&(u[1][n-2][1]), 1, send, neigh[3], max_iter+2, MPI_COMM_WORLD,&requests[7]);
}
double t1,time;
//Main Loop
while (iter <= max_iter && FrobNorm > tolCheck){
//Timing
if (iter == 1) {
MPI_Barrier(MPI_COMM_WORLD);
if (rank == 0) {
t1 = MPI_Wtime();
}
}
if (iter % FrobCheckFreq == 0){
FrobNorm = 0;
}
//Synchronize
MPI_Waitall(noRequests,requests,MPI_STATUSES_IGNORE);
for(i=1; i<n-1;i++){ //x
for(j=1; j<n-1;j++){ //z
for(k=1; k<N-1;k++){ //y
//Gauss-seidel iteration
//Red Points
if( (i+j+k) % 2 == 0){
if (iter % FrobCheckFreq == 0){
u_tmp = u[i][j][k];
u[i][j][k] = h*(u[i-1][j][k] + u[i+1][j][k] + u[i][j-1][k] + u[i][j+1][k] + u[i][j][k-1] + u[i][j][k+1] + delta_sq*f[i][j][k]);
FrobNorm += (u[i][j][k] - u_tmp) * (u[i][j][k] - u_tmp);
} else{
u[i][j][k] = h*(u[i-1][j][k] + u[i+1][j][k] + u[i][j-1][k] + u[i][j+1][k] + u[i][j][k-1] + u[i][j][k+1] + delta_sq*f[i][j][k]);
}
}
}
}
}
//Red points done, send and recv to black points
if (neigh[0] != -1){
// send and recieve above
MPI_Irecv(&(u[1][0][1]), 1, send, neigh[0], iter, MPI_COMM_WORLD,&requests[0]);
MPI_Isend(&(u[1][1][1]), 1, send, neigh[0], iter, MPI_COMM_WORLD,&requests[1]);
}
if (neigh[1] != -1){
// send and recieve left
MPI_Irecv(&(u[0][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], iter, MPI_COMM_WORLD, &requests[2]);
MPI_Isend(&(u[1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], iter, MPI_COMM_WORLD,&requests[3]);
}
if (neigh[2] != -1){
// send and recieve right
MPI_Irecv(&(u[n-1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], iter, MPI_COMM_WORLD,&requests[4]);
MPI_Isend(&(u[n-2][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], iter, MPI_COMM_WORLD,&requests[5]);
}
if (neigh[3] != -1){
// send and recieve below
MPI_Irecv(&(u[1][n-1][1]), 1, send, neigh[3], iter, MPI_COMM_WORLD,&requests[6]);
MPI_Isend(&(u[1][n-2][1]), 1, send, neigh[3], iter, MPI_COMM_WORLD,&requests[7]);
}
//Synchronize
MPI_Waitall(noRequests,requests,MPI_STATUSES_IGNORE);
for(i=1; i<n-1;i++){ //x
for(j=1; j<n-1;j++){ //z
for(k=1; k<N-1;k++){ //y
//Gauss-seidel iteration
//Black Points
if( (i+j+k) % 2 != 0) {
if (iter % FrobCheckFreq == 0){
u_tmp = u[i][j][k];
u[i][j][k] = h*(u[i-1][j][k] + u[i+1][j][k] + u[i][j-1][k] + u[i][j+1][k] + u[i][j][k-1] + u[i][j][k+1] + delta_sq*f[i][j][k]);
FrobNorm += (u[i][j][k] - u_tmp) * (u[i][j][k] - u_tmp);
} else{
u[i][j][k] = h*(u[i-1][j][k] + u[i+1][j][k] + u[i][j-1][k] + u[i][j+1][k] + u[i][j][k-1] + u[i][j][k+1] + delta_sq*f[i][j][k]);
}
}
}
}
}
//Black points done, send and recv for next iteration
if (neigh[0] != -1){
// send and recieve above
MPI_Irecv(&(u[1][0][1]), 1, send, neigh[0], iter, MPI_COMM_WORLD, &requests[0]);
MPI_Isend(&(u[1][1][1]), 1, send, neigh[0], iter, MPI_COMM_WORLD,&requests[1]);
}
if (neigh[1] != -1){
// send and recieve left
MPI_Irecv(&(u[0][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], iter, MPI_COMM_WORLD, &requests[2]);
MPI_Isend(&(u[1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[1], iter, MPI_COMM_WORLD,&requests[3]);
}
if (neigh[2] != -1){
// send and recieve right
MPI_Irecv(&(u[n-1][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], iter, MPI_COMM_WORLD, &requests[4]);
MPI_Isend(&(u[n-2][1][0]), (n-2)*N, MPI_DOUBLE, neigh[2], iter, MPI_COMM_WORLD,&requests[5]);
}
if (neigh[3] != -1){
// send and recieve below
MPI_Irecv(&(u[1][n-1][1]), 1, send, neigh[3], iter, MPI_COMM_WORLD,&requests[6]);
MPI_Isend(&(u[1][n-2][1]), 1, send, neigh[3], iter, MPI_COMM_WORLD,&requests[7]);
}
if (iter % FrobCheckFreq == 0) {
MPI_Allreduce(&FrobNorm,&FrobNorm,1,MPI_DOUBLE,MPI_SUM,MPI_COMM_WORLD);
}
if (iter % FrobCheckFreq == 0 && rank == 0 && iter != 0){
printf("Iter = %d --- FrobNorm = %f\n",iter,FrobNorm);
}
iter += 1;
if(n == max_iter && rank == 0) {
printf("Stopped due to iter_max \n");
}
}
if (rank == 0) {
printf("Stopped in iteration number: %d\n",iter-1);
}
MPI_Waitall(noRequests,requests,MPI_STATUSES_IGNORE);
*tolerance = sqrt(FrobNorm);
MPI_Barrier(MPI_COMM_WORLD);
if (rank == 0) {
time = MPI_Wtime() - t1;
printf("Average iteration runtime %f seconds (skipping iter == 0) !\n",time/max_iter);
}
}