Since Mike McCourt is in dire need of flexible multiphysics infrastructure
I've started to look at some of the newly implement Mat stuff in PETSc (and my
head is spinning).
Could the author's of these things take a look at my comments and respond
(hopefully with changes, but I can change things also).
Stream of consciousness writing because I can't get my head around it all.
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MatCreateNest() (and VecCreateNexs()). Does not have the the proper
construction process that always goes through MatCreate_Nest() (and
VecCreate_Nest()). This needs to be fixed. Should add something like
MatNestAddBlocks() or similar name for putting the blocks in after the call to
MatCreate_Nest().
MatCreateNest() seems to assume that all Mat's live on all processes in the
outer Mat communicator. How hard would it be to change the code so that each
block could live on some subcommunicator?
MatCreateSubMatrix() will it eventually have MatSetValues() that directs
requests down to the appropriate block?
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MatCreateSubMatrix(). Again not the proper construction process built on
MatCreate_SubMatrix() (when the heck was this written 10 years ago before we
enforced that rule.) This needs to be fixed. What's with the manual page
description "Creates a composite matrix that acts as a submatrix" what the heck
does 'composite' mean here and what does "acts as a submatrix" mean?
MatSubMatrixUpdate() what does the documentation "full matrix in the
submatrix" mean? The full matrix is bigger than the submatrix so how can it be
in the submatrix. Terrible phrase.
MatSubMatrixUpdate() why have this routine, why not model on
MatGetSubMatrix() and have a single interface function
MatCreateSubMatrix(Mat,IS,IS,MatRuse,Mat *)?
MatCreateSubMatrix() terrible name, why not MatGetSubMatrixImplicit()?
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MatCreateLocalRef() again with no proper construction with
MatCreate_LocalRef() (come on guys get with the program)
MatCreateLocalRef() 'Gets a logical reference to a local submatrix, for use
in assembly' what does this mean? Assembly in PETSc is reserved for inside
MatAssembly,VecAssembly it should not be used for the process of setting values
into the matrix. Thus this sentence is meaningless gibberish. Could possible
be something like 'Gets a logical reference to a local submatrix, for use in
putting values into that block with MatSetValues() or MatSetValuesLocal()?
MatCreateLocalRef() How/why is this different than MatCreateSubMatrix()? Could
they be merged into one construct? Why is this a 'local' ref, is it a block
only only on this process?
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How is MatCreateBlockMat() which fortunately has the proper constructor
related to MatCreateNest()? Do they serve the same purpose? Different purposes?
Can they be merged together?
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In the end we want to be able to run 'multphysics' codes where it is a
command line switch between 'block matrix' storage of the global Jacobian where
each block is a submatrix of the entire matrix and stored itself for example in
AIJ format; or one big honking AIJ matrix. In both cases the user calls
MatSetValues() or MatSetValuesLocal() to put values in and has no switches in
the code they write that depends on the matrix format, things like
MatGetSubMatrix() and MatGetSubMatrices() work transparently on them. How do
these four Matrix classes take us in that direction?
Thanks
Barry
