#include <stdio.h>
#include <unistd.h>
#include <mpi.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>



//Example compilation
//mpicc allreduce_starter.c -lm -o allreduce_starter

//Example execution
//mpirun -np 1 -hostfile myhostfile.txt ./allreduce_starter




int main(int argc, char **argv) {

  int my_rank, nprocs;

  MPI_Init(&argc,&argv);
  MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
  MPI_Comm_size(MPI_COMM_WORLD,&nprocs);

  if (nprocs!=4)
  {
    if (my_rank==0)
    {
      printf("Please enter 4 process ranks.\n\n");
    }
    MPI_Finalize();
    return 0;
  }

  //Each rank generates a different number of elements
  //Assume the ranks do not know how many elements each other produce
  //The values are hard coded here, but in practice they will not be
  double * data;

  int nElems=0;

  if (my_rank==0)
  { 
    nElems=3;
    data=(double *)malloc(sizeof(double)*nElems);
  }
  else if (my_rank==1)
  { 
    nElems=5;
    data=(double *)malloc(sizeof(double)*nElems);
  }
  else if (my_rank==2)
  { 
    nElems=2;
    data=(double *)malloc(sizeof(double)*nElems);
  }
  else if (my_rank==3)
  { 
    nElems=7;
    data=(double *)malloc(sizeof(double)*nElems);
  }

  //Initialize data to be equal to the iteration
  for (int i=0; i<nElems; i++)
  {
    data[i]=i;
  }


  //Write code here

  


  MPI_Finalize();
  return 0;
}