#include <mpi.h>
#include <stdio.h>
#include <stdio.h>
#include <unistd.h>
#include<stdlib.h>
  
  
  int main(int argc, char **argv)
  {
  int nprocs;
  int rank;

  MPI_Init(&argc,&argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  int nRows, nCols;
  int matrix[nRows][nCols];
  
  printf("Enter the number of rows and columns that your matrix has and the number of processes that you would like to use \n");
  scanf("%d%d%d", &nRows, &nCols, &nprocs);
  
  
	
	  int row;
	  int col;
		
	  for(row = 0; row < nRows; row++)
	  {
	    for(col = 0; col < nCols; col++)
	    {
	          matrix[row][col] = row*nCols + col ;
	    }
	  }
	
 
  	int totalElems;
  	totalElems=nRows * nCols;
 	
  	int global_sum=0;
 	int maxSize=98;/* max size is 98 since there are a maximum of 9 rows and 9 columns */
  	int cursorPos; /* A variable that we will use to access the jth column element of the ith row. */
  	int startCursorPos; /* The index that a process starts. */
  	int endCursorPos; /* The index that a process  ends. */
    int localSum;
  	startCursorPos=rank; /* Each process starts at its rank. I.e rank 0 starts at position o, 1 at position 1,.....*/
  	endCursorPos= (rank+1)+(((totalElems-nprocs)/nprocs)*nprocs); /* The cursor position where each process stops. */ 
  	int getCursorPosElem(){
  		return matrix[cursorPos/nCols][cursorPos%nCols];
 		 };
  	/* A fuction that accesses the element stored at the cursors position we increment the cursor pos by the number of processes since processes access 
  	elemente in an alternating manner and a process accesses elements after all othe processes have accessed their elements*/
  	for(cursorPos=startCursorPos;cursorPos<endCursorPos;cursorPos+=nprocs){
	  	int localSum;
	  	localSum=0;
  		/* Uptate the local sum with the element stored at the cursors position*/
  		localSum = localSum+getCursorPosElem ();
		printf("local Sum by rank %d equals %d\n", localSum, rank);
	  }
	  	 
  	MPI_Reduce(&localSum, &global_sum, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
  	printf("Final sum = %d \n", global_sum);
  

  MPI_Finalize();

  return 0;
}