[petsc-dev] MatGetLocalSubMatrix, MatLocalReference implementation

[Jed Brown]

On Sun, Nov 21, 2010 at 00:01, Barry Smith <bsmith at mcs.anl.gov> wrote:

> Just pick what you want, but if you do use "local" then it should match the
> use of "local" in other parts of PETSc (for example a local Vec is a ghosted
> "part" of a global Vec). For example, if you suddenly starting calling
> unghosted sequential Vec parts of a global Vec it would be confusing. So
> just use your judgement, I can't tell what you are asking half the time so
> don't always expect a coherent response.


Okay, this thing I need denotes a subset of the usual "local Vec".  You
introduced "global IS" to denote subsets of the global Vec so I think my
calling it "local IS" is entirely consistent.  I tend to think of the
relations in the sense of

  (global Vec, global IS) induces, via the "local" operation, (local Vec,
local IS)

rather than

  (global Vec, local Vec) induces, via the "get IS" operation, (global IS,
local IS)

although this diagram commutes with a suitable ISLocalToGlobalMapping.

I would like to rename your DMCompositeGetGlobalIndices to
DMCompositeGetISLocalToGlobalMappings (and make it return
ISLocalToGlobalMappings, obviously).  Since the function was never called
(never declared in a public header), I can't imagine this will inconvenience
anyone.

BTW, that function currently uses a PFIDENTITY hack which is really gross if
the user gets crazy and uses single precision, I'll make it use integer
arithmetic.

Jed
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