Why can’t I access muhray 8 lines from the bottom? The print lines that start with “!!” work correctly but I can’t seem to get the right values at the very end.
Here is my output:
[computer@node01 ~]$ mpiexec -n 8 ./presum 1000
!! proc0's array is size 125 and goes from 1 to 1
proc0's array is size 125 and goes from 4693173 to 1819307369
!! proc2's array is size 125 and goes from 1 to 1
proc2's array is size 125 and goes from 4693173 to 1819307369
!! proc3's array is size 125 and goes from 1 to 1
proc3's array is size 125 and goes from 4693173 to 1819307369
!! proc1's array is size 125 and goes from 1 to 1
proc1's array is size 125 and goes from 4693173 to 1819307369
!! proc4's array is size 125 and goes from 1 to 1
proc4's array is size 125 and goes from 4693173 to 1819307369
!! proc5's array is size 125 and goes from 1 to 1
proc5's array is size 125 and goes from 4693173 to 1819307369
!! proc6's array is size 125 and goes from 1 to 1
proc6's array is size 125 and goes from 4693173 to 1819307369
!! proc7's array is size 125 and goes from 1 to 1
proc7's array is size 125 and goes from 4693173 to 1819307369
Here is the code in question:
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
//max size of the data array to split up
#define MAXSIZE 1000000
//methods
int checkInput(int nprocs, int argc, char *argv[], int id);
//mpi send & rec tags
int ARSIZE = 0; //array size
int ARR = 1; //array
int MSM = 2; //slave sum
int main(int argc, char *argv[]) {
int ARsize; /*size of the array to pre-sum*/
int id; /*process id number*/
int nprocs; /*number of processors*/
int i, j, k; /*counters*/
int muhsize; /*size of personal array to calculate*/
int * muhray; /**/
//MPI framework
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
MPI_Comm_rank(MPI_COMM_WORLD, &id);
MPI_Barrier(MPI_COMM_WORLD);
//pull input, check values, return ARsize
ARsize = checkInput(nprocs, argc, argv, id);
//set up array, serial run, send out chunks
if (!id) {
//variables only the zero node needs
int data[ARsize]; /*full original array of numbers*/
int chunkSize, upper, lower; /*vars to determine cunksize to send out*/
int smoothCount = 0; /*BOOL for uneven division chunksize*/
//fill array with numbers
for (i = 0; i < ARsize; i++) {
data[i] = 1;
}
//sequential solution here
//determine chunkSize
chunkSize = (int) (ARsize/nprocs);
if (ARsize % nprocs != 0) {
chunkSize = chunkSize + 1;
smoothCount = 1;
}
//send chunks of data to procs
for (i = 0; i < nprocs; i++) {
lower = i * chunkSize;
upper = ((i+1) * chunkSize) - 1;
if (i == nprocs-1 && smoothCount == 1) {
upper = ARsize-1;
}
int intarray[(upper-lower)];
for (k = lower, j = 0; k <= upper; k++, j++) {
intarray[j] = data[k];
}
if(i > 0) {
//send array size
MPI_Send(&j, 1, MPI_INT, i, ARSIZE, MPI_COMM_WORLD);
//send actual array
MPI_Send(intarray, j, MPI_INT, i, ARR, MPI_COMM_WORLD);
}
//zero no send to self, this data used later for all nodes calc
else {
muhsize = j;
int muhray[muhsize];
for (j = 0; j <= chunkSize; j++) {
muhray[j] = intarray[j];
}
printf("!! proc%d's array is size %d and goes from %d to %d\n", id, muhsize, muhray[0], muhray[(muhsize-1)]);
}
}
}
else {
MPI_Recv(&muhsize, 1, MPI_INT, 0, ARSIZE, MPI_COMM_WORLD, &status);
int muhray[muhsize];
MPI_Recv(muhray, muhsize, MPI_INT, 0, ARR, MPI_COMM_WORLD, &status);
printf("!! proc%d's array is size %d and goes from %d to %d\n", id, muhsize, muhray[0], muhray[(muhsize-1)]);
fflush(stdout);
}
printf("proc%d's array is size %d and goes from %d to %d\n", id, muhsize, muhray[0], muhray[muhsize]);
fflush(stdout);
//MPI_Send(&muhsize, 1, MPI_INT, 0, MSM, MPI_COMM_WORLD);
MPI_Finalize();
}
//pull input, check values, return ARsize
int checkInput(int nprocs, int argc, char *argv[], int id) {
int size;
if (nprocs % 2 != 0 || nprocs == 6 || nprocs > 8) {
if (!id) printf("run with 2^k procs, (1 >= k <= 3)\n");
fflush(stdout);
MPI_Finalize();
exit(1);
}
if (argc != 2) {
if (!id) printf("Usage: presum [array size (max: %d)]\n", MAXSIZE);
fflush(stdout);
MPI_Finalize();
exit(1);
}
size = atoi(argv[1]);
if (size <= nprocs) {
if (!id) printf("search range must be greater than processor count\n");
fflush(stdout);
MPI_Finalize();
exit(1);
}
if (size > MAXSIZE) {
if (!id) printf("array size must be less than or equal to %d\n", MAXSIZE);
fflush(stdout);
MPI_Finalize();
exit(1);
}
return size;
}
The problem you have is very likely with scopes of variables. For instance here:
you declare
int muhray[muhsize];inside the scope of theelseconstruct. When you exit this scopemuhrayis destroyed as it is a local variable. What you are using in the lastprintfseems to be an uninitializedint * muhray;declared immediately after the main.Note that while they have the same name these two are different variables.