[OMPI users] Memory management and data structures with OpenMPI.

[Pranav Sumanth]

Greetings, 

I need help understanding how I can better manage memory in my code. 
sizeof(x)=8 (file main.cpp) and this is always equal to the number of processes 
spawned. How do I ensure that sizeof(x) = 1 and that it is a 1D array of size 
num (from main.cpp).

I would like to import utils.h as a static library import. How best should I 
structure my code? I would also be very grateful if I am pointed to suitable 
references to be better aware of using ND arrays, vectors and data structures 
with OpenMPI.

Thanks, 
Best Regards,
Pranav



My main.cpp is:

#include <iostream>
#include <utils.h>
#include <mpi.h>

using namespace std;

int main(int argc, const char * argv[]) {
    
    
    MPI_Init(NULL, NULL);
    
    float start = 0., end = 1.;
    int num = 100;
    
    double *x = linspace(start, end, num);
    
    
    for(int i=0;i<num;i++){
        cout << *(x + i) <<endl;
    }
    
    
    MPI_Finalize();
    
    
    return 0;
    
}



My utils.h is:

#ifndef utils_h
#define utils_h


#endif /* utils_h */

#include <iostream>
#include <vector>
#include <cassert>
#include <mpi.h>

using namespace std;


double * linspace(double start_in, double end_in, unsigned long int num_in)
{
    /* This function generates equally spaced elements and returns
    an array with the results */
    
    
    int size, rank;
    
    double start = static_cast<double>(start_in);
    double end = static_cast<double>(end_in);
    unsigned long int num = static_cast<unsigned long int>(num_in);
    
    double * linspaced;
    linspaced = new double[num];
    
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    
    assert(num!=0);
    
    if (num == 1)
    {
        *(linspaced) = start_in;
        return linspaced;
    }
    
    
    double delta = (end - start) / (num - 1);
    
    
    for(int i=rank; i < num - 1; i += size)
    {
        
        // cout << "i = " << i << endl;
        *( linspaced + i) = start + delta * i;
    }
    linspaced[num-1] = end; // I want to ensure that start and end
    // are exactly the same as the input

    
    cout << "size-of-linspaced : " << sizeof(linspaced) << endl;
    return linspaced;
    
}


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