Fwd: matrices without diagonals...

[Todd Munson]

The problem I encountered is in:

   src/mat/impls/aij/seq/aijfact.c

The MatICCFactorSymbolic_SeqAIJ does not check for empty rows when the 
number of levels is set to zero.  For a larger number of levels it does 
get checked.

I changed my code to add the diagonal into the matrix to prevent the error 
from occuring...

Cheers, Todd.

On Tue, 30 Oct 2007, Barry Smith wrote:

>
>  Todd,
>
>   You are correct!
>
>   There is a routine MatMissingDiagonal(). Routines that
> implicitly require all diagonal entries in the data structure
> are suppose to call this routine and check the flag before
> chugging along. It appears that this code is not always
> called when needed.
>
>   Note that many methods DO NOT require the diagonal entries
> so MatMissingDiagonal() should not be called willy-nilly
> but only when needed.
>
>   Please report to petsc-maint at mcs.anl.gov the routines that
> crash for you and we will add the error checking (note matrix
> type in the report).
>
>   Barry
>
>
> On Tue, 30 Oct 2007, Todd Munson wrote:
>
>>
>> I'll let you all decide the best course of action.  I'm just going to make the
>> statement that a core dump is not a valid way to signify that the diagonal
>> does not exist.  Something needs to be done...
>>
>> SeqAIJ has a PetscScalar* for the various diagonal entries; not sure why the
>> others do not do something similar if the diagonal is always required.
>>
>> Todd.
>>
>> On Tue, 30 Oct 2007, Matthew Knepley wrote:
>>
>>> I may be wrong, but I think a lot of AIJ methods need the diagonal. Do we
>>> think
>>> it is feasible to relax this? I would be more for filling the diagonal
>>> with zeros
>>> automatically.
>>>
>>>   Matt
>>>
>>> ---------- Forwarded message ----------
>>> From: Todd Munson <tmunson at mcs.anl.gov>
>>> Date: Oct 30, 2007 9:18 AM
>>> Subject: matrices without diagonals...
>>> To: Barry Smith <bsmith at mcs.anl.gov>
>>> Cc: Matthew Knepley <knepley at mcs.anl.gov>
>>>
>>>
>>>
>>> Barry,
>>>
>>> We discussed this yesterday and I want to come to a conclusion before I go
>>> and change any code.  The problem is that some of the matrix I have do not
>>> have diagonal entries...in fact both the rows and columns do not have any
>>> nonzeros.  Rather than PETSc terminating gracefully and telling me the
>>> problem, I get a segmentation violation and a core dump.
>>>
>>> There are two questions:
>>>
>>>   1) Which functions require a diagonal?
>>>   2) Should these functions check for the diagonal and abort with a useful
>>>      error message?
>>>
>>> My feeling is that the diagonal is required only in a few cases and it may
>>> not even be necessary, but I've been known to be wrong before.  Most of
>>> the code should work without requiring diagonal entries, which is why it
>>> should only check for them when necessary.
>>>
>>> Todd.
>>>
>>>
>>>
>>> --
>>> 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
>>>
>>>
>>
>>
>
>