[petsc-users] VecView doesn't work properly with DA global vectors

[Barry Smith]

On Mar 21, 2011, at 8:11 PM, Алексей Рязанов wrote:

> Hi
> 
> Is it ok, that VecView doesn't work properly with vectors, obtained with DACreateGlobalVector function, or im doing something wrong?
> In my program I create 5x5 da and global vector, corresponding to this da. 
> Then each of 4 process writes its rank to its own local elements using DAVecGet(Restore)Array functions.
> Then i use VecView to visualize my global vector. 
> And i see, that each process owns elements with different values.
> Where is the mistake?
> 
   VecView() for DM global vectors present the vector entries in the global natural ordering. Since PETSc divides the domain with DA into squareish blocks when you print the values on a process (by calling DAVecGetArray) it is not in the global natural ordering. Hence the two are different.

  Barry
   
> Thank you very much!
> 
> Alexey Ryazanov.
> 
> 
> 
> CODE:
> 
> #include "petscksp.h"
> #include "petscda.h"
> static char help[] = "VecVeiw doesn't work properly with DAGlobalVectors";
> int main(int argc,char **args)
> {
>   Vec		GlobalVec;
>   DA		da;
>   PetscInt	rank, dof, stencil_width, M, N, m, n, p, x, y, z, i, j;
>   PetscScalar	**array;
>   PetscErrorCode ierr;
> 
>   PetscInitialize(&argc,&args,(char *)0,help);
>   MPI_Comm_rank(PETSC_COMM_WORLD, &rank);
> 
>   M=N=5; dof=1; stencil_width=1;
>   ierr = DACreate2d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_BOX, M, N, PETSC_DECIDE, PETSC_DECIDE, dof, stencil_width, PETSC_NULL, PETSC_NULL, &da);
> 								CHKERRQ(ierr);
>   ierr = DACreateGlobalVector(da,&GlobalVec);			CHKERRQ(ierr);
> 
>   ierr = DAGetCorners(da,&x,&y,&z,&m,&n,&p);			CHKERRQ(ierr);
> 
>   ierr = DAVecGetArray(da, GlobalVec, &array);			CHKERRQ(ierr);
>   for(i=y; i<y+n ; i++)
>     for(j=x; j<x+m; j++)
> 	array[i][j]=rank;
>   ierr = DAVecRestoreArray(da, GlobalVec, &array);		CHKERRQ(ierr);
> 
>   ierr = VecView(GlobalVec, PETSC_VIEWER_STDOUT_WORLD);		CHKERRQ(ierr);
> 
>   ierr = VecDestroy(GlobalVec);					CHKERRQ(ierr);
>   ierr = DADestroy(da);	  					CHKERRQ(ierr);
>   ierr = PetscFinalize(); 					CHKERRQ(ierr);
>   return 0;
> }
> 
> 
> OUTPUT:
> 
> Process [0]
> 0
> 0
> 0
> 1
> 1
> 0
> 0
> 0
> 1
> Process [1]
> 1
> 0
> 0
> 0
> 1
> 1
> Process [2]
> 2
> 2
> 2
> 3
> 3
> 2
> Process [3]
> 2
> 2
> 3
> 3
>