dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxxx>]

I think that would be a good idea. And the name is an accurate description
of what is going on.

/Johan


> A possibility would be a function "FEM::assembleBCresidual".
>
> Garth
>
> On Fri, 2005-12-02 at 09:11 +0100, Garth N. Wells wrote:
>> Quoting Anders Logg <logg@xxxxxxxxx>:
>>
>> > This looks strange to me, but maybe I don't understand it.
>> >
>> > What if you don't even have a vector x? What vector should x should
>> > you then give as an argument?
>>
>> If you don't have a vector x, you don't want to use this function :-).
>> It's
>> basically returning the Dirichlet boundary condition "residual".
>>
>> >
>> > Maybe it is better to just call the standard version of applyBC()
>> > without x and then do
>> >
>> > b *= -1.0;
>> > b += x;
>>
>> This would add x to all elements of b, not just to elements where
>> Dirichlet
>> boundary conditions are applied. I originally used the old applyBC for a
>> vector
>> to use an analogous procedure to the above, but this required two
>> temporary
>> vectors to be created, initialised and have boundary conditions applied
>> at each
>> Newton iteration (in addtion to the usual assemble of b) - not very
>> nice.
>>
>> >
>> > This would be two lines of code extra (one if you put them on the same
>> > line... :-). It's probably better to put this in the Newton solver
>> > since the Newton solver knows why this operation should be performed.
>>
>> The Newton solver knows nothing about the boundary coniditons. The BC's
>> need to
>> be applied by the user in the resdiudal vector b. This is done in the
>> class
>> NonlinearFunction.
>>
>> A possibility is a function that inserts components of x into b (rather
>> than the
>> BC value), where Dirichlet BCs are applied. PETSc has a function to the
>> set the
>> vector R, where F(u) = R is being solved, so R would contain the
>> Dirichlet BCs.
>>
>>
>> Garth
>>
>> >
>> > /Anders
>> >
>> >
>> > On Thu, Dec 01, 2005 at 02:16:12PM +0100, dolfin@xxxxxxxxxx wrote:
>> > > Commit from garth (2005-12-01 14:16 CET)
>> > > -----------------
>> > >
>> > > Functions for applying boundary conditions to the RHS vector only
>> > now accept the solution vector x. Where Dirichlet boundary conditions
>> > are applied, b = x - bc.The is useful for applying boundary conditions
>> > within Newton iterations.
>> > >
>> > > This is not consistent with the other applyBC functions which return
>> b = bc
>> > (no minus sign). This is due to the definition of the nonlinear
>> function
>> > F(u)=0.
>> > > For Poisson's equation, I've been using the format F(u) = (grad
>> v,grad u) -
>> > (v,f), hence the need for the minus. Is there a preference as to how
>> we
>> > set-up nonlinear problems?
>> > >
>> > > Would it be better to use a different name for funtions that return
>> the
>> > difference between the current approximate solution and the Dirichlet
>> BC?
>> > >
>> > >   dolfin  src/kernel/fem/FEM.cpp       1.43
>> > >   dolfin  src/kernel/fem/dolfin/FEM.h  1.23
>> > >
>> > > _______________________________________________
>> > > DOLFIN-dev mailing list
>> > > DOLFIN-dev@xxxxxxxxxx
>> > > http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>> > >
>> >
>> > --
>> > Anders Logg
>> > Research Assistant Professor
>> > Toyota Technological Institute at Chicago
>> > http://www.tti-c.org/logg/
>> >
>> > _______________________________________________
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>> > DOLFIN-dev@xxxxxxxxxx
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>> >
>>
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> --
> Dr. Garth N. Wells
> Faculty of Civil Engineering and Geosciences
> Delft University of Technology
> Stevinweg 1
> 2628 CN Delft
> The Netherlands
>
> tel.     +31 15 278 7922
> fax.     +31 15 278 6383
> e-mail   g.n.wells@xxxxxxxxxxxxxxx
> url      http://www.mechanics.citg.tudelft.nl/~garth
>
>
>
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