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

[Geoffrey Irving]

On Fri, Nov 15, 2013 at 3:40 PM, Geoffrey Irving <irving at naml.us> wrote:
> On Fri, Nov 15, 2013 at 3:37 PM, Matthew Knepley <knepley at gmail.com> wrote:
>> On Fri, Nov 15, 2013 at 5:31 PM, Geoffrey Irving <irving at naml.us> wrote:
>>>
>>> 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"?
>>
>>
>> Damn, you are right.
>
> Great, that makes it easier to understand.  I'm trying to reverse
> engineer the general definitions of all the fields in PetscFEM.  It's
> okay that they're not written down yet; it's probably better for me to
> do this myself anyways to get a better feel for everything.

On irving/doc-cleanup as 30f909e1127f96586767d1a276195e9ca312e66c.

Geoffrey