[petsc-dev] Jed!!!

[Jed Brown]

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

> On Apr 26, 2014, at 11:54 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> Barry Smith <bsmith at mcs.anl.gov> writes:
>> 
>>>   Mat nest is just an optimization. That, BTW makes it impossible to do the simplest tests of your code!!
>> 
>> It is intended to be used with MatGetLocalSubMatrix and
>> MatSetValuesLocal.  It would be significant complexity (including memory
>> scalability) to support MatSetValues, and supporting that mode would
>> encourage people to write code that needs refactoring to perform.  At
>> least that was my thinking.  If you are assembling with a global
>> MatSetValues, MATNEST doesn't offer much so just don't use it.
>> 
>> How do you want to change this?
>
>   Somehow have a way of testing the resulting Jacobian against a
>   “known” accurate one. 

-dm_mat_type aij -snes_type test?

Comparison of this type is a "monolithic" operation, like LU is a
monolithic operation, so why not use a monolithic format?  I'm not
objecting to something else, but I want the code to be as simple as
possible.

>   We all know how users fuck up Jacobians; given that this one is even
>   more complicated to build we sure as hell should have a way of
>   comparing it to a finite difference Jacobian. And for that
>   scalability and efficiency don’t mater.
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