[petsc-dev] MATCOMPOSITE as fallback for matrix-matrix multiplication

[Isaac, Tobin G]

One thought: we could extend MatReuse with MAT_INITIAL_MATRIX_GET_VALUES to indicate that a matrix that implements MatGetValues() is desired, to allow some user intent.


On March 9, 2019 7:44:06 PM EST, Matthew Knepley <knepley at gmail.com> wrote:
>On Sat, Mar 9, 2019 at 4:42 PM Isaac, Tobin G via petsc-dev <
>petsc-dev at mcs.anl.gov> wrote:
>
>>
>> Let's say I want to do Newton-Krylov on some DAG of computations.
>> Building the Jacobian is programmatic from the chain rule, requiring
>> just a lot of matrix-matrix multiplications in the correct sequence.
>>
>> If it really is more efficient for two Jacobians to be contracted
>into
>> a matrix with random access, that's great, but if it's not, or if
>> the appropriate implementation of MatMatMult_X_Y does not exist,
>> having a MATCOMPOSITE is better than nothing.
>>
>> So why not make MATCOMPOSITE something that our matrix-matrix
>> multiplication routines return when a specialization isn't found?
>> It moves the "Not Implemented" warning from MatMatMult() to
>> whenever I try to do something other than multiply with the output,
>> but in some situations that's desirable.
>>
>> I'd be interested to hear what people think.
>>
>
>I think this is a good idea. The most important thing is to maintain
>transparency, so that the output
>makes this clear in -ksp_view and we are easily able to see what
>someone
>has produced.
>
>   Matt
>
>
>> Thanks,
>>   Toby
>>
>>
>>