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MPI_test.cpp
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MPI_test.cpp
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/*EECS 587 HW3
by Yuhui Shi
The entire matrix is transposed */
#include <cstdio>
#include <cstdlib>
#include <mpi.h>
#include <cmath>
#define PI 3.141592653589793
#define N_ITER 500
double** arr_mem_loc(const int nrow, const int n);
void arr_mem_clc(double** arr, const int nrow, const int n);
void arr_init_val(double** local_arr, const int rank, const int uni_chunk_size, const int nrow, const int n);
int get_nrow(const int rank, const int numproc, const int n);
int main(int argc, char **argv) {
// parse the arguments, get the matrix size
int n;
if (argc > 1) {
n = atoi(argv[1]);
}
else {
n = 1000; // defualt value
}
int numproc, rank;
int nrow, uni_chunk_size;
double time;
/*******************Initialization*****************/
// intialize and find the basic info
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &numproc);
// partition the matrix by row, get the partition size
nrow = get_nrow(rank, numproc, n);
uni_chunk_size = (int)ceil((double)n / numproc);
//printf("HERE!!!\n");
//printf("Chunk size: = %d, nrow = %d\n", uni_chunk_size, nrow);
//printf("proc:%d, ncol: %d\n", rank, nrow);
// allocate the memory for the array
double **local_arr;
local_arr = arr_mem_loc(nrow, n);
arr_init_val(local_arr, rank, uni_chunk_size, nrow, n);
MPI_Barrier(MPI_COMM_WORLD);
// get the current time
if (rank == 0)
time = MPI_Wtime();
/*******************Iterations****************/
double* first_row;
double* last_row;
double* halo_up;
double* halo_bt;
MPI_Request up_request;
MPI_Request bt_request;
MPI_Status up_status;
MPI_Status bt_status;
// do iterations
double** new_arr = new double*[nrow];
for (int i = 0; i < nrow; i++) {
new_arr[i] = new double[n];
}
for (int iter = 0; iter < N_ITER; iter++) {
//printf("Iteration : %d\n", iter);
first_row = local_arr[1];
last_row = local_arr[nrow];
halo_up = local_arr[0];
halo_bt = local_arr[nrow + 1];
// send the halo rows to neighbours
int up_nb_rank = (rank - 1 + numproc) % numproc;
int bt_nb_rank = (rank + 1 + numproc) % numproc;
MPI_Isend(first_row, n, MPI_DOUBLE, up_nb_rank, 0, MPI_COMM_WORLD, &up_request);
MPI_Isend(last_row, n, MPI_DOUBLE, bt_nb_rank, 0, MPI_COMM_WORLD, &bt_request);
MPI_Recv(halo_up, n, MPI_DOUBLE, up_nb_rank, 0, MPI_COMM_WORLD, &up_status);
MPI_Recv(halo_bt, n, MPI_DOUBLE, bt_nb_rank, 0, MPI_COMM_WORLD, &bt_status);
// update the cells
for (int i = 0; i < nrow; i++) {
for (int j = 0; j < n; j++) {
// do not update the boundary cell
if (j == 0 || j == n-1)
new_arr[i][j] = local_arr[i + 1][j];
else {
// average of all neighbours and it self
new_arr[i][j] = (local_arr[i][j - 1] + local_arr[i][j] + local_arr[i][j + 1]
+ local_arr[i + 1][j - 1] + local_arr[i + 1][j] + local_arr[i + 1][j + 1]
+ local_arr[i + 2][j - 1] + local_arr[i + 2][j] + local_arr[i + 2][j + 1])/9.0;
}
}
}
// copy back the values
for (int i = 0; i < nrow; i++) {
for (int j = 0; j < n; j++) {
local_arr[i + 1][j] = new_arr[i][j];
}
}
}
// clear the memory
for (int i = 0; i < nrow; i++) { delete[] new_arr[i]; }
delete[] new_arr;
/**************************Calulate the verification sum*****************************/
// calculate the local verification sum
int global_i;
double local_veri_sum = 0;
for (int i = 1; i < nrow + 1; i++) {
global_i = uni_chunk_size * rank + i - 1;
for (int j = 0; j < n; j++) {
if (global_i == j)
local_veri_sum += local_arr[i][j];
}
}
// add up all local verification sum
double total_veri_sum = 0;
MPI_Reduce(&local_veri_sum, &total_veri_sum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
MPI_Barrier(MPI_COMM_WORLD);
// calculate and print out the time
if (rank == 0) {
time = MPI_Wtime() - time;
printf("Verification sum = %.6f, Wall time = %.2f\n", total_veri_sum, time);
}
arr_mem_clc(local_arr, nrow, n);
MPI_Finalize();
return 0;
}
int get_nrow(const int rank, const int numproc, const int n) {
int nrow;
nrow = (int)ceil((double)n / numproc);
if (n % nrow != 0) {
if (rank == numproc - 1) {
nrow = n % nrow;
}
}
return nrow;
}
double** arr_mem_loc(const int nrow, const int n) {
double** arr = new double*[nrow + 2]; // add two halo rows
for (int i = 0; i < nrow + 2; i++) {
arr[i] = new double[n];
}
return arr;
}
void arr_mem_clc(double** arr, const int nrow, const int n) {
for (int i = 0; i < nrow+2; i++) {
delete[] arr[i];
}
delete[] arr;
}
void arr_init_val(double** local_arr, const int rank, const int uni_chunk_size, const int nrow, const int n) {
int global_i;
for (int i = 1; i < nrow + 1; i++) {
global_i = uni_chunk_size * rank + i - 1;
for (int j = 0; j < n; j++) {
if (j == 0) {
local_arr[i][j] = 0;
}
else if (j == n - 1) {
local_arr[i][j] = 5 * sin(PI * pow(global_i/(double)n, 2));
//local_arr[i][j] = 123;
//printf("%.4f\n", local_arr[i][j]);
}
else {
local_arr[i][j] = 0.5;
}
}
}
}