Troubles in MPI -> Failing at address: (nil) - c

Question

I'm a beginner in C and MPI and i'm trying to do a program to multiply 2 matrix in MPI.
But I don't kwno what is wrong in my code.
I'm try do 'slice' the matrix M1 in n lines and send then to another process do multiply and broadcast de matrix M2 After I make a Gather to build the final matrix M3.
I make this:
mpirun -n 2 matrix
But I receive a error in terminal:
[adiel-VirtualBox:07921] *** Process received signal ***
[adiel-VirtualBox:07921] Signal: Segmentation fault (11)
[adiel-VirtualBox:07921] Signal code: (128)
[adiel-VirtualBox:07921] Failing at address: (nil)
--------------------------------------------------------------------------
mpirun noticed that process rank 0 with PID 7921 on node adiel-VirtualBox exited on signal 0 (Unknown signal 0).
--------------------------------------------------------------------------
2 total processes killed (some possibly by mpirun during cleanup)
mpirun: clean termination accomplished
Can anyone help me?
Here's my code:
#include <stdio.h>
#include <stdlib.h>
#include "mpi.h"
//#include "mpe.h"
#include <math.h>
void printMatrix(double *M, int m, int n) {
int lin, col;
for (lin=0; lin<m; lin++) {
for (col=0; col<n; col++)
printf("%.2f \t", M[(lin*n+col)]);
printf("\n");
}
}
double* allocateMatrix(int m, int n){
double* M;
M = (double *)malloc(m*n*sizeof(double));
return M;
}
int main( int argc, char *argv[] )
{
int rank, size;
int m1,n1,m2,n2;
int row, col,ctrl,i,k,lines,proc;
double *M1, *M2, *M3, **vp, *v;
MPI_Init( &argc, &argv );
MPI_Comm_rank( MPI_COMM_WORLD, &rank );
MPI_Comm_size( MPI_COMM_WORLD, &size );
m1 = m2 = n1 = n2 = 3;
lines = (int)ceil(n1/size);
v = (double *)malloc(lines*n1*sizeof(double));
M2 = allocateMatrix(m2,n2);
M3 = allocateMatrix(m1,n2);
if(rank==0)
M1 = allocateMatrix(m1,n1);
//startin matrix
for (col = 0; col < n1; col++){
for (row = 0; row < m1; row++) {
if(rank==0)
M1[(row*m1+col)] = 0;
M2[(row*m2+col)] = 0;
M3[(row*m1+col)] = 0;
}
}
//startin pointers with 0
for(i=0;i<lines*n1;i++)
v[i] = 0;
//populate
if(rank == 0){
for (col = 0; col < n1; col++){
for (row = 0; row < m1; row++) {
M1[row*m1+col] = row*3+(col+1);
M2[(row*m2+col)] = 1;
}
}
}
//---------------------sharing and multiply---------------//
//slicing M1 and sending to other process
if(rank == 0){
proc = size-1;
//for each line
for(row = 0;row<m1;row++){
ctrl = floor(row/lines);
//on each column
for(col=0;col<n1;col++){
v[(ctrl*n1)+col] = M1[(row*n1)+col];
}
if(row%lines == (lines - 1)){
if(proc!=0){
MPI_Send(v,lines*n1,MPI_DOUBLE,proc,1, MPI_COMM_WORLD);
proc--;
//clearing pointers
for(i=0;i<lines*n1;i++)
v[i] = 0;
}
}
}
}
//MPI_Bcast(m1, m*n, MPI_DOUBLE, 0, MPI_COMM_WORLD);
MPI_Bcast(M2, m2*n2, MPI_DOUBLE, 0, MPI_COMM_WORLD);
//receiving process
if(rank!=0)
MPI_Recv(v,lines*n1,MPI_DOUBLE,0,1,MPI_COMM_WORLD, MPI_STATUS_IGNORE);
for(row=0;row<lines;row++){
if(v[row*n1]!=0){
for (col = 0; col < n1; col++){
double val = 0.0;
for(k=0;k<m1;k++){
val += v[(row*n1)+k] * M2[(k*n1)+col];
}
M3[((size-1-rank)*size*n1)+(row*n1)+col] = val;
}
}
}
if(rank!=0){
for(row = 0; row < lines; row++){
MPI_Gather(&M3[((size-1-rank)*size*n1)+(row*n1)], n1, MPI_DOUBLE, &M3[((size-1-rank)*size*n1)+(row*n1)], n1, MPI_DOUBLE, 0, MPI_COMM_WORLD);
}
}
if(rank == 0){
printf("matrix 1------------------------\n");
printMatrix(M1,m1,n1);
printf("matrix 2------------------------\n");
printMatrix(M2,m2,n2);
printf("matrix 3------------------------\n");
printMatrix(M3,m1,n2);
}
MPI_Finalize();
return 0;
}

Answer 1

For one thing, doing all of your sends before the broadcast, and all of the receives after it is asking for trouble. I can easily see that leading to MPI resource exhaustion or deadlock failures. In such a small input that shouldn't arise, but you should fix it regardless. I'll take another look after that.