PETSc Doubt

static char help[] = "Introduction to the Vec environment.\n\n";


#include "petsc.h"


int main(int argc, char *argv[])
{
    PetscInt     i,rank,n;      /*Two variables for storing the rank and the total number of processes.*/
    PetscInt     N;              /*This stores the length of each vector.*/
    Vec          x;              /*This would be the main working vector of this program.*/
    PetscScalar  one=1.0;

    PetscInitialize(&argc,&argv,(char*)0,help);
    MPI_Comm_rank (PETSC_COMM_WORLD, &rank);/*Stores the values of rank of each process in the variable rank.*/
    MPI_Comm_size (PETSC_COMM_WORLD, &n);   /*Similarly stores the total number of processes.*/
    VecCreate(PETSC_COMM_SELF,&x);
    VecSetSizes(x,rank+1,PETSC_DECIDE);     /*Now setting the sizes.*/
    VecSetFromOptions(x);
    VecGetSize(x,&N);
    VecSet(x,one);
    PetscInt ix[N];
    PetscScalar  y[N],Sum=0.0;          /*This would be the storage term for the Sum and Current Element.*/

    for(i=0;i<N;i++)
        ix[i]=i;
    VecAssemblyBegin(x);
    VecAssemblyEnd(x);

    VecGetValues(x,N,ix,y);

    for(i=0;i<N;i++)
    {
        Sum+=y[i];

        PetscPrintf(PETSC_COMM_SELF,"Process:%d Y[%d]=%d\n",rank,i,y[i]);
    }

    VecDestroy(&x);
    PetscPrintf(PETSC_COMM_SELF,"The sum of the vector elements from process %d is %d\n",rank,Sum);


    PetscFinalize();

    return 0;
}