[petsc-dev] I don't understand PETSCPARTITIONSHELL

[Barry Smith]

  So shell can 1) use some random partitioner or 2) allow the user to provide the partitioning?

  This is a strange combination. Won't it be better to have PETSCPARTIONERRANDOM and PETSCPARTITIONERSHELL?

  You could use the random for the tests (but as command line options not hardwired in the examples).

   Barry


> On Feb 9, 2017, at 9:45 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> 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
>  
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>   Barry
> 
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> 
> -- 
> 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