Barry,
Thanks a lot. I’d like to use this for a nonlinear variant of a
block-gauss-seidel smoother. I would like to use MatInvertBlockDiagonal for
speeding up my variant.

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I think I can work with this, however I also have the problem to turn my
initial matrix into one with a blocksize of 3.When I call:
MatConvert(A, MATBAIJ, MAT_INITIAL_MATRIX, Dinverse);
Then the matrix Dinverse has blocksize 1 which comes from A. I checked the
blocksize before the conversion and it was 3, so it seems to get lost.
What is the correct (and elegant) way to turn a matrix into a block matrix?
Best
Cyrill
On 19/09/16 17:18, "Barry Smith" <bsm...@mcs.anl.gov> wrote:
>
> Cyrill,
>
> This is very specialized for implementing point block Jacobi; I don't
> think it is something you would want to use directly.
>
> If you do want to use it, it simply returns the inverses of the block
> diagonals in column major form. You can then call MatSetValues() with with
> each of those blocks into another PETSc matrix. values[i*bs*bs] is the
> starting point of each block in the array.
>
> Barry
>
>> On Sep 19, 2016, at 4:55 AM, Cyrill Vonplanta <cyrill.von.pla...@usi.ch>
>> wrote:
>>
>> Dear PETSc-Users,
>>
>> I would like to use the inverted block diagonals of a a matrix. I have seen
>> the function MatInvertBlockDiagonal() but I don’t know how to create a
>> matrix out of them or an array of block matrizes.
>>
>> Does anyone have an example on how to use **values to create a PETSc matrix?
>>
>> Thanks
>> Cyrill
>