I am working with a serial code and trying to parrallize it. The code is suppose

ID: 3795811 • Letter: I

Question

I am working with a serial code and trying to parrallize it. The code is suppose to implement the sieve of Eratosthenes and find the primes up to a given limit. I continue to get this error message and would like to know what could be the fix?

#include
#include
#include
#include //looks in the include directory
static bool isPrime(long val)
{
if (val < 2) return false;
for (long i = 2; i * i <= val; i++) {
if ((val % i) == 0) return false;
}
return true;
}

int main(int argc, char *argv[])
{
int comm_sz;
int my_rank;

MPI_Init(NULL,NULL); //initializes MPI
MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

if (my_rank == 0){
printf("Prime Sieve v1.0 [MPI] "); //changed "serial" to "MPI"
}
// check command line
if (argc != 2) {fprintf(stderr, "usage: %s maximum ", argv[0]); exit(-1);}
const long top = atol(argv[1]);
if (top < 23) {fprintf(stderr, "error: maximum must be at least 23 "); exit(-1);}
printf("computing prime numbers up to but not including %ld ", top);

const int my_start = my_rank * (long)top / comm_sz;
const int my_end = (my_rank+1) * (long)top / comm_sz;

// allocate array
bool* array = new bool[top];

// start time
MPI_Barrier(MPI_COMM_WORLD);//barrier implemented before time start
timeval start, end;
gettimeofday(&start, NULL);

// initialize array
for (long i = 2 + my_rank; (i*i) < top; i+=comm_sz) { //assigned in a cylic
array[i] = true;
}

// remove multiples
for (long i = my_start; (i * i) < my_end; i++) { // just finished splitting array between processes, now
    long j = i * i;                                //I need to reduce into final array in the process 0
    while (j < top) {
      array[j] = false;
      j += i;
    }
}
// initiallize new array
bool* array2 = new bool[top];
    for (long i = 2 + my_rank; (i*i) < top; i+=comm_sz) { //assigned in a cylic
    array[i] = true;

// reduction
for (long i = my_start; i <= my_end; i++){
// if (array[i] == true){
MPI_Reduce(&array[i],&array2[i],1,MPI::BOOL,MPI_LXOR,0,MPI_COMM_WORLD);
}

// end time
gettimeofday(&end, NULL);
double runtime = end.tv_sec + end.tv_usec / 1000000.0 - start.tv_sec - start.tv_usec / 1000000.0;
printf("compute time: %.4f s ", runtime);

// print part of result from array2
if (my_rank == 0){
for (long i = 2; i < 10; i++) {
    if (array2[i]) {
      printf(" %ld", i);
    }
}
printf(" ...");
for (long i = top - 10; i < top; i++) {
    if (array2[i]) {
      printf(" %ld", i);
    }
}
printf(" ");

// verify result
if (top < 10000000) {
    for (long i = 2; i < top; i++) {
      if (array2[i] != isPrime(i)) {
        fprintf(stderr, "ERROR: wrong answer for %ld ", i);
        exit(-1);
      }
    }
}
}
delete [] array2;
delete [] array;
MPI_Finalize(); //finalizes mpi
return 0;
}
}

2 total processes failed to start [qwt10path finder Project2]$ mpirun n 2. /my executable. /sieve 2000000 mpirun was unable to launch the specified application as it could not access or execute an executable Executable ./myexecutable. /sieve Node pathfinder while attempting to start process rank 0.

Explanation / Answer

Solution 1.

It may happen if you have already installed openMPI and not only MPICH2, then you should execute the below commands as root:

root~# update-alternatives --config mpirun

There are 2 choices for the alternative mpirun (providing /usr/bin/mpirun).

Selection | Path | Priority | Status

Then you should select the MPICH version, as above, to run normally.

Solution 2.

Put the full path to tau_exec in the command line. It is possible that your PATH is not the same on all the nodes. Then , it would not be able to locate the executable anywhere where the path isn't correct.

Note:

Don't remane the output file. Keep the default a.out as the name of output file.

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