DAcreate2d process layout order

[Sean Dettrick]

Hi,

I'm trying to use DACreate2d and KSP in my existing MPI application.  I 
already have a Cartesian communicator established, and I set 
PETSC_COMM_WORLD equal to it and then call PetscInitialize.

This works fine on a prime number of CPUs, because there is only one 
possible ordered MPI layout in one dimension.  But with a non-prime 
number there are two possible ordered layouts and it just happens that 
my 2D CPU layout (determined by MPI_Cart_create) is the transpose of the 
PETSc 2D CPU layout. 

Is there a way to organize the DA layout more explicitly than with 
DACreate2d?   Or to tell PETSc to transpose its CPU order?  I also 
wonder about the 3D case.

thanks
Sean