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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