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). > > 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? -- Anders
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