[petsc-users] MatView question

[Treue, Frederik]

Hi,

I'm confused about the matview command, or rather, it's output. The following lines of code:
  int rank;
  MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
  MatView((*FD).ddx,PETSC_VIEWER_STDOUT_WORLD);
  int fr,lr;
  MatGetOwnershipRange((*FD).ddx,&fr,&lr);
printf("process %d has rows %d to %d\n",rank,fr,lr);
Produce the following output:
>mpirun -np 4 ./petsclapl
 Matrix Object: 1 MPI processes
  type: mpiaij
row 0: (0, 5)  (1, 5)  (12, 0)  (13, 0)  (108, 0)  (109, 0)
 row 1: (0, -5)  (1, 0)  (2, 5)  (12, 0)  (13, 0)  (14, 0)  (108, 0)  (109, 0)  (110, 0)
[snip]
process 0 has rows 0 to 30
process 1 has rows 30 to 60
process 2 has rows 60 to 90
process 3 has rows 90 to 120

My question is this: How come the MatView command states 1 MPI processes, while, when I use GetOwnershipRange, the (expected) division into ¼ of the rows at each process is reported? Is the MatView "processes" the process of the viewer? And more importantly, what is the actual position of my matrix - is it on 1 or on 4 processes?

---
yours sincerily
Frederik Treue

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