On Tue, Dec 23, 2008 at 05:13:57PM +0000, Garth N. Wells wrote: > > > Anders Logg wrote: > > On Tue, Dec 23, 2008 at 05:02:47PM +0000, Garth N. Wells wrote: > >> > >> Anders Logg wrote: > >>> On Tue, Dec 23, 2008 at 03:28:44PM +0000, Garth N. Wells wrote: > >>>> Anders Logg wrote: > >>>>> Why is there a pseudo time-stepping algorithm built into > >>>>> NonlinearPDE::solve? > >>>> So that the PDE can be solved with a series of Newton steps and boundary > >>>> conditions can functions of pseudo time t. > >>>> > >>>> Will it not converge if we just call the > >>>>> NewtonSolver directly? > >>>>> > >>>> Not always. > >>> ok. > >>> > >>>>> It would be better if the LinearPDE and NonlinearPDE only provided a > >>>>> layer between the forms and the linear/nonlinear solvers. > >>>>> > >>>>> If we need a pseudo time-stepping algorith, it can be built into > >>>>> NewtonSolver, or maybe another class? > >>>>> > >>>> I wouldn't put it NewtonSolver. Best to keep NewtonSolver abstract (i.e. > >>>> unaware of PDEs) and just let it perform Newton solves. We could create > >>>> a class like NonlinearSolver or NonlinearPDESolver. > >>> NonlinearPDESolver would not be consistent with the current LinearPDE > >>> class which is in some sense is a solver for linear PDEs. > >>> > >>>> Most nonlinear PDEs are sufficiently complex and the solution methods so > >>>> diverse that for non-trivial problems I would expect that a user will > >>>> implement the solution procedure, and a NonlinearPDE class is not very > >>>> useful. Perhaps we could just provide more building blocks to make the > >>>> construction of nonlinear solvers easy? > >>> I would be inclined to just remove the NonlinearPDE class and > >>> implement the pseudo time-stepping directly in the demo: > >>> > >> This is what I do in practice all the time, so removing NonlinearPDE is > >> fine with me. > > > > ok. I'll fix when I get a chance. > > > >>> while t < T: > >>> > >>> A = assemble() > >>> b = assemble() > >>> bc.apply() > >>> > >>> newton_solver.solve(...) > >>> > >>> f.t = t > >>> bc.t = t > >> I added a Python class to take care of the time (it's in dolfin_time.py). > >> > >>> t += dt > >>> > > > > Wouldn't it be simpler to just use a float? If one defines > > > > f = Function(V, "t*sin(x[0])") > > > > then one may automatically change the variable t by > > > > f.t = t > > > > thanks to some fancy magic Johan cooked up in the new Python Function > > class(es). > > > > Looks very clever. > > >>> I've also been thinking about the LinearPDE class. Perhaps we should > >>> rename it to VariationalProblem? > >>> > >> Sounds good. Solving nonlinear PDEs usually involves solving a series of > >> variational problems, so we could later develop a design in which a > >> VariationalProblem can be sent to a nonlinear solver. > > > > ok. Should it be VariationalProblem or just VarProblem? > > > > VariationalProblem > > Garth
ok. -- Anders
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