MPI_Scatter and MPI_Gather dont work - c

Question

Hallo Iam trying to make a simlpe parralel program in C language uing MPI. Program should find maximum in array. Root process should send chunks of array to all processes using MPI_Scatter and then gather results by MPI_Gather. When I run the program i get general error like this:
Perhaps this Unix error message will help:
Unix errno: 14
Bad address
I know that there is some problem with MPI_Scatter and MPI_Gather or with the values I am sending to this functions.
I was trying to find the solution, but I found nothing what could be useful.
Here is my code:
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFSIZE 9
int max(int *buf, int N){
int i;
int value = 0;
for(i=0; i<N; i++){
if (buf[i]>value){
value = buf[i];
}
}
return value;
}
int main(int argc, char** argv)
{ int size, rank;
int slave;
int *buf;
int *buf1;
int *buf2;
int i, n, value;
MPI_Status status;
/* Initialize MPI */
MPI_Init(NULL, NULL);
/*
* Determine size in the world group.
*/
MPI_Comm_size(MPI_COMM_WORLD, &size);
if ((BUFSIZE % size) != 0) {
printf("Wrong Bufsize ");
return(0);
}
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (rank==0) {
buf = (int *)malloc(BUFSIZE*sizeof(int));
buf2 = (int *)malloc(size*sizeof(int));
printf("\n Generated array: \n");
for(i=0; i<BUFSIZE; i++){
buf[i] = rand() % 20;
printf("%d, ", buf[i]);
}
printf("\n");
printf("\n Sending values to processes:");
printf("\n -----------------------------");
}
buf1 = (int *)malloc((BUFSIZE/size)*sizeof(int));
MPI_Scatter(buf, BUFSIZE/size, MPI_INT, buf1, BUFSIZE/size, MPI_INT, 0, MPI_COMM_WORLD);
value = max(&buf1[0], BUFSIZE/size);
printf("\n Max from rocess %d : %d \n", rank, max(&buf1[0], BUFSIZE/size));
MPI_Gather(&value, 1, MPI_INT, buf2, 1, MPI_INT, 0, MPI_COMM_WORLD);
if (rank == 0){
printf("\n Max value: %d", max(&buf2[0], size));
}
MPI_Finalize();
return(0);
}

Answer 1

Initialize your pointers to NULL, and track them.
use buf1 instead of &buf1[0], is more clear.
free your buffers before MPI_Finalize() with:
if(bufferPionter != NULL) free(bufferPionter);
If something is wrong with a pointer will crash in the free call. In the max function, If all your numbers are less than zero the maximun is zero. i fix that.
int max(int *buf, int N){
int i;
int value = N? buf[0] : 0;
for(i=0; i<N; i++){
if (buf[i]>value){
value = buf[i];
}
}
return value;
}
Best regards!