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" <[email protected]> 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()); >>> _______________________________________________ >>> DOLFIN-dev mailing list >>> [email protected] >>> http://www.fenics.org/mailman/listinfo/dolfin-dev >>> > > _______________________________________________ > DOLFIN-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/dolfin-dev _____________________________________________ > DOLFIN-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/dolfin-dev _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
