[petsc-dev] what's q in snes ex62

[Geoffrey Irving]

On Fri, Nov 15, 2013 at 3:21 PM, Matthew Knepley <knepley at gmail.com> wrote:
> On Fri, Nov 15, 2013 at 5:09 PM, Geoffrey Irving <irving at naml.us> wrote:
>>
>> Is the second equation the weak form of incompressibility?  If so, why
>> isn't q u?  It's used as q several places throughout the code, so it
>> seems more likely to be my misunderstanding than a typo.
>>
>>   < \nabla v, \nabla u + {\nabla u}^T > - < \nabla\cdot v, p > + < v, f > = 0
>>   < q, \nabla\cdot v >                                                     = 0
>
> u, v \in V and p, q \in P, and hopefully \div V = P for stability.

Are you using the same variables as

    http://fenicsproject.org/documentation/dolfin/dev/python/demo/pde/stokes-iterative/python/documentation.html

If so, maybe that line should be

    < q, \nabla\cdot u >

I.e., "u" instead of "v"?

Geoffrey