[petsc-users] Question about petsc4py createWithArray function

[Matthew Knepley]

On Thu, May 2, 2024 at 12:53 PM Samar Khatiwala <
samar.khatiwala at earth.ox.ac.uk> wrote:

> Hello, I have a couple of questions about createWithArray in petsc4py: 1)
> What is the correct usage for creating a standard MPI Vec with it?
> Something like this seems to work but is it right?: On each rank do: a =
> np. zeros(localSize) v = PETSc. Vec(). createWithArray(a,
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> Hello,
>
> I have a couple of questions about createWithArray in petsc4py:
>
> 1) What is the correct usage for creating a standard MPI Vec with it? Something like this seems to work but is it right?:
>
> On each rank do:
> a = np.zeros(localSize)
> v = PETSc.Vec().createWithArray(a, comm=PETSc.COMM_WORLD)
>
> Is that all it takes?
>
>
That looks right to me.

> 2) Who ‘owns’ the underlying memory for a Vec created with the createWithArray method, i.e., who is responsible for managing it and doing garbage collection? In my problem, the numpy array is created in a Cython module where memory is allocated, and a pointer to it is associated with a numpy ndarray via PyArray_SimpleNewFromData and PyArray_SetBaseObject. I have a deallocator method of my own that is called when the numpy array is deleted/goes out of scope/whenever python does garbage collection. All of that works fine. But if I use this array to create a Vec with createWithArray what happens when the Vec is, e.g., destroyed? Will my deallocator be called?
>
> No. The PETSc struct will be deallocated, but the storage will not be
touched.

  Thanks,

     Matt

> Or does petsc4py know that it doesn’t own the memory and won’t attempt to free it? I can’t quite figure out from the petsc4py code what is going on. And help would be appreciated.
>
> Thanks very much.
>
> Samar
>
>
>

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