[petsc-dev] I don't understand PETSCPARTITIONSHELL

[Matthew Knepley]

On Thu, Feb 9, 2017 at 9:36 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Matt,
>
>    I don't understand PETSCPARTITIONSHELL.
>
>    Why does it exist? Why not just use PETSCPARTITIONSIMPLE when no other
> partitioner exists?
>
>    Why is it called shell? Other XXSHELL allow users to provide their own
> routines to provide the XX functionality, this does not seem to do that. So
> it is not shell in the PETSc sense.
>
>    Why hard wire examples to use it? Why not just have list it as an args:
> in the test cases with -petscpartitioner_type shell (but why not just
> simple?) putting the ugly shit directly into the source code seems
> unnecessary and annoying.


1) The two partitioners do different things:

  Simple: It divides the cells evenly without reordering.

  Shell: It allows the user to set a prescribed partition

It is clear to me that Shell is needed because sometimes you want to
prescribe the partition, if for no
other reason than you know that a certain partition has a bug. Simple is
questionable, but we were
using it for testing.

2) It is called Shell because for a shell the user prescribes the behavior
directly, which is exactly what happens.

3) I did not put it in arguments because it can get very long, and I
thought it was easier to see and manipulate in the code. I am open to
moving it.

  Matt


>
>
>   Barry
>
>
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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