[petsc-users] [PATCH 2/2] Call KSPSetFromOptions before setting fieldsplit-specific options

[Jed Brown]

Umut Tabak <u.tabak at tudelft.nl> writes:

> On 09/08/2013 05:51 PM, Jed Brown wrote:
>> Umut Tabak <u.tabak at tudelft.nl> writes:
>>
>>
>> Looks like it's converging, albeit somewhat slowly, and your operator
>> scaling is terrible (not necessarily a problem, but full-space
>> fieldsplit methods work much better if you non-dimensionalize so that
>> the fields have similar scales).
>
> Indeed, something I am aware of,
>
> A00
>
> is ill-conditioned
>
> A11
>
> block is indefinite, even worse.

A11 indefinite could lead to the Schur complement being singular.  The
approach breaks down if that's the case.  A11 singular or negative
semi-definite is the standard case.

> I have been looking for some scaling options that might work but until 
> now no success so far...

You need to read the literature for problems of your type.  There are a
few possible approaches to approximating the Schur complement.  The
splitting into blocks also might not be very good.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 835 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130908/5b8c10ee/attachment.pgp>