dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Jan 19, 2009 at 10:38:16PM -0500, Hatef Monajemi wrote:
> Hi,
> 
> Yes, You are right. I am interested in a problem similar to Navier-Stokes but
> not exactly that.
> 
> I took a look at Unicorn, Although it was not updated, I figured out how the
> solver was written based on Fixed Point iterations.
> 
> My question referes to dolfin VariationalProblem.cpp at line 75:
> 
> "void VariationalProblem::solve(Function& u0, Function& u1)"
> 
> This means that one should be able to solve the nonlinear problems with more
> than one variable by just augmenting the state-space vector and solving the
> whole state with Newton's iteration.

Yes, that should be possible in principle, but there's no guarantee
that it will always converge.

> The only difference with the linear case should be the fact that
> instead of solving for the solution (U) dirrectly, the nonlinear
> problem should be sovled for an increment (\delta U) around a
> guessed solution (say U0) and correcting the U0 in every Newton's
> iteration.

Yes.

> To me it should be possible to solve a nonlinear problem with Newton's
> iteration based on what I can see in  the afforementioned file in (dolfin/fem)
> .Please correct me if I am wrong. However the following peice of code gives an
> error like "Missing eval() for user-defined function (must be overloaded)". and
> in my usr-define functions such as Source, etc eval() is overloaded. I do not
> see where the problem arises. Any opinion?
> 
> {VariationalProblem nlpde(a,L,bcs,true);
>   nlpde.solve(U,P);}

Could you send the rest of the code as well (the form files). I won't
have time to debug your code but I can try running it once to see if I
can spot the problem.

-- 
Anders


>  
> 
> Thanks
> 
> Hatef
> 
>  
> 
> >Hi Hatef,
> 
> >It sounds as if you are interested in the Navier-Stokes equations, or
> 
> >similar? If so, you may want to check out the Unicorn solver:
> 
> >http://www.fenics.org/wiki/Unicorn
> 
> >Direct any Unicorn questions to: unicorn-...@xxxxxxxxxx
> >
> >Best,
> >Johan
> 

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