[petsc-dev] MatNest in petsc4py with empty submatrices

[Lawrence Mitchell]

On 17/02/16 14:47, Chris Eldred wrote:
> Hey All,
> 
> I was wondering if anyone had used MatNest with petsc4py. I am having
> issues trying to create a MatNest where some of the submatrices are
> empty. In PETSc, I can just pass NULL in the array that I give to
> MatCreateNest and it works fine. However, the following code

We use it, but haven't used it with empty slots.

> nest_list = [[None,None],[None,None]]
> nest_list[0][0] = some matrix
> nest_list[0][1] = some matrix
> nest_list[1][0] = some matrix
> A = PETSc.Mat().createNest(nest_list,comm=PETSc.COMM_WORLD)
> 
> fails with:
>   File "Mat.pyx", line 445, in petsc4py.PETSc.Mat.createNest
> (src/petsc4py.PETSc.c:103202)
> TypeError: Cannot convert NoneType to petsc4py.PETSc.Mat
> 
> Is there an equivalent to NULL in petsc4py (there doesn't appear to be one)?
> 
> If all of the entries in nest_list are filled, everything works fine.
> 
> Any help would be appreciated!

Maybe a patch like this to petsc4py?

diff --git a/src/PETSc/Mat.pyx b/src/PETSc/Mat.pyx
index f281ba0..490c58e 100644
--- a/src/PETSc/Mat.pyx
+++ b/src/PETSc/Mat.pyx
@@ -460,7 +460,10 @@ cdef class Mat(Object):
         tmp1 = oarray_p(empty_p(nr*nc), NULL, <void**>&cmats)
         for i from 0 <= i < mr:
             for j from 0 <= j < mc:
-                cmats[i*mc+j] = (<Mat?>mats[i][j]).mat
+                if mats[i][j] is None:
+                    cmats[i*mc+j] = NULL
+                else:
+                    cmats[i*mc+j] = (<Mat?>mats[i][j]).mat
         if isrows is not None:
             tmp2 = oarray_p(empty_p(nr), NULL, <void**>&cisrows)
             for i from 0 <= i < mr: cisrows[i] = (<IS?>isrows[i]).iset


Untested.

If you want to pass null isrows and iscols as well you'll need to do a
similar thing there.

Cheers,

Lawrence

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