DetermineRowRankFromLocalSize.cpp

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/* \file DetermineRowRankFromLocalSize.cpp
 * \brief: routine to determine, from local size of a matrix or vector (in terms of number 
 * of rows), a vector of global size  which for each row of the matrix or vector, determines
 * what cpu this row belong to.
 */
 
#include <stdio.h>
#include <math.h>
#include "../../../shared/shared.h"
#include "../../../shared/Numerics/types.h"
 
int* DetermineRowRankFromLocalSize(int global_size,int localsize,ISSM_MPI_Comm comm){
 
   /*intermediary: */
   int i,j;
   int my_rank=0;
   int num_procs=0;
   int lower_row,upper_row;
 
   /*output: */
   int* RowRank=NULL;
 
   ISSM_MPI_Comm_rank(comm,&my_rank);
   ISSM_MPI_Comm_size(comm,&num_procs);
 
   /*allocate: */
   RowRank=xNew<int>(global_size);
 
   /*Gather all local_size values into alllocalsizes, for all cpus*/
   int* alllocalsizes=xNew<int>(num_procs);
   ISSM_MPI_Allgather(&localsize,1,ISSM_MPI_INT,alllocalsizes,1,ISSM_MPI_INT,comm);
 
   /*From all localsizes, get lower row and upper row*/
   lower_row=0;
   upper_row=lower_row+alllocalsizes[0];
   for(j=lower_row;j<upper_row;j++)RowRank[j]=0;
 
   for(i=1;i<num_procs;i++){
      lower_row=lower_row+alllocalsizes[i-1];
      upper_row=upper_row+alllocalsizes[i];
      for(j=lower_row;j<upper_row;j++)RowRank[j]=i;
   }
   xDelete<int>(alllocalsizes);
 
   return RowRank;
}