dolfin team mailing list archive

[Patrick Riesen <priesen@xxxxxxxxxxxxxxx>]

Ouuch, i had apply(b) in void F instead of apply(b, x) ...

thank you very (!!) much, Garth, this solved the problem!

best regards,
patrick


Garth N. Wells wrote:
> Check that you're applying the Dirichlet boundary conditions correctly, 
> i.e. using
>
> void apply(GenericMatrix& A, GenericVector& b, const GenericVector& x) 
> const;
>
> which is for applying bcs within Newton iterations.
>
> Garth
>
> Patrick Riesen wrote:
> > Hi
> >
> > so i corrected my form-file for the new representation of L = F and a 
> > = (F')u. However the solving still repeats and does not converge, the 
> > problem remains.
> >
> > i don't know if it has to with L being expected as a nonlinear form 
> > but my L = F is actually linear in u?
> >
> > it is linear in u because i put the nonlinear part ( the computation 
> > of the variable viscosity ) in another form file, so in the main form 
> > file (hence in L) i only have something like
> >
> > eta*dot(D(v),D(u))       (D() is the symmetric part of grad(u))
> >
> > and eta = trace(mult(D(u),D(u))^(exponent) i get from somewhere else.
> >
> > patrick
> >
> >
> >
> >
> > Anders Logg wrote:
> > > Yes, the bilinear form should be the linearized nonlinear form (not
> > > minus).
> > >
> > > Note that with UFL, it's now possible to just write down the nonlinear
> > > form
> > >
> > >   (v, F(u)) = 0 for all v
> > >
> > > and then let UFL compute the linearization.
> > >
> > >
> > >
> > > ------------------------------------------------------------------------
> > >
> > > __> ouuuuu, this might be the lucky guess, i wasn't aware of that...
> > >
> > > Ostien, Jakob T wrote:
> > > > In a totally blind guess, I believe that for a nonlinear problem, 
> > > > the linear
> > > > form used to require a minus sign (DOLFIN 0.8), but now (DOLFIN 
> > > > 0.9+) the
> > > > minus sign is built into NewtonSolver.  You might want to check that 
> > > > first.
> > > >
> > > > Jake
> > > >
> > > >
> > > > On 5/1/09 3:09 AM, "Patrick Riesen" <priesen@xxxxxxxxxxxxxxx> wrote:
> > > >
> > > > > hello!
> > > > >
> > > > > i want to update my powerlaw solver from dolfin 0.8 to dolfin 0.9.2.
> > > > > the solver class is derived from the NonlinearProblem class and i
> > > > > followed the CahnHillard-demo to do something similar for updating 
> > > > > from
> > > > > 0.8 to 0.9.2.
> > > > >
> > > > > However I have a problem which i do not understand:
> > > > >
> > > > > If i hand the created forms to VariationalProblem and let it solve, 
> > > > > all
> > > > > works fine and in the second iteration the newton solver converges 
> > > > > (if i
> > > > > initialize a newtonian problem just for checking).
> > > > >
> > > > > if i do
> > > > >
> > > > > newtonsolver.solve(*this,uu->vector());
> > > > >
> > > > > the problem gets solved as well, i.e. all bcs and my own void F and 
> > > > > void
> > > > > J get called but it does not converge, it's like the problem gets 
> > > > > solved
> > > > > over and over again and the solution is added, because in the end i 
> > > > > get
> > > > > a solution but it's the number of iterations \times velocity.
> > > > >
> > > > > i tried all kinds of things (with/without pointers, no cast/cast,
> > > > > different classes for problem/solve ...) but i don't get it, i miss
> > > > > something.
> > > > >
> > > > > maybe somebody has a hint or does see my error and can help me turn on
> > > > > the light?
> > > > >
> > > > > many thanks in advance
> > > > >
> > > > > patrick
> > > > >
> > > > >
> > > > > below is a code snippet of the main part:
> > > > > /----------------------------------------------------------------------------- 
> > > > >
> > > > > --
> > > > >    _uu = new Function(*_V);
> > > > >    Function* __uu = dynamic_cast<Function*>(_uu);
> > > > >
> > > > >    // create the forms
> > > > >    a_powstokes = new PowerlawStokesBilinearForm(*_V,*_V);
> > > > >    PowerlawStokesBilinearForm* _a_powstokes =
> > > > > dynamic_cast<PowerlawStokesBilinearForm*>(a_powstokes);
> > > > >    _a_powstokes->w0 = *__uu;
> > > > >    _a_powstokes->eta1 = eta;
> > > > >    _a_powstokes->eta2 = d_eta;
> > > > >
> > > > >
> > > > >    L_powstokes = new PowerlawStokesLinearForm(*_V);
> > > > >    PowerlawStokesLinearForm* _L_powstokes =
> > > > > dynamic_cast<PowerlawStokesLinearForm*>(L_powstokes);
> > > > >    _L_powstokes->w0 = *__uu;
> > > > >    _L_powstokes->eta1 = eta;
> > > > >    _L_powstokes->f = f;
> > > > >
> > > > > //   VariationalProblem pde(*a_powstokes, *L_powstokes, bcs, true);
> > > > > //   pde.solve(fluid.velocity(),fluid.pressure());
> > > > >
> > > > >    newtonsolver.solve(*this,__uu->vector());
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