[petsc-dev] making DA more light weight

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>   I suggest the following:  
>
>     ISLocalToGlobalCreate() takes a block size. 
>
>     ISLocalToGlobalApply() will then do the integer arithmetic if bs > 1
>
>     ISLocalToGlobalApplyBlock() will just use the given indices 
>
>    Then Mat/VecSetLocalToGlobal() will only have one mapping and DMDACreate() will only create the block version 

That's what I meant in my other mail (rationalizing that integer
division should not ruin performance; needs to be tested).  I think this
is worthwhile and not hard, but it's small fish compared to VecScatter,
which requires several times as much memory.  See my other mail with
full stack traces for each large allocation.
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