On Wednesday October 20 2010 10:39:11 Marie Rognes wrote: > A while back (in connection with the blueprint > https://blueprints.launchpad.net/dolfin/+spec/solver-interfaces) there > was a discussion regarding the interface to VariationalProblem. Anders > and Marie have discussed this a bit further, in particular with regard > to the adaptive solution of variational problems, and suggest the > interface outlined below. (This suggestion involves a change in the > interface, and hence the double post to both the dolfin and > fenics-mailinglists)
I guess this discussion comes on top of the previous one? Because that blueprint mentioned a lot more than what is mentioned here. I also assume this is limited to the Python interface as doing stuff like derivative behind the scene is limited to PyDOLFIN? > >From Marie's perspective, the main reasons for changing the interface are > > (a) The current "nonlinear=true" variable seems superfluous and > suboptimal > (b) We should allow for automated computation of the Jacobian (when > needed). > > For (nonlinear) variational problems, the interface should read > > pde = VariationalProblem(Form F, Form jacobian=None, ...) > pde.solve(u) > > where "F" is a Form of rank 1, "jacobian" is a Form of rank 2, and "u" > is a Function. Such a pde will be treated as a nonlinear variational > problem. The "jacobian" would be an optional argument. If not given, > > jacobian = derivative(F, u) > > will be used for the nonlinear solve if needed (for instance as the > left-hand side of the Newton iteration). > > Additionally, we have the interface for linear problems (as before) > > pde = VariationalProblem(Form a, Form L, ...) > pde.solve(u) / u = pde.solve() > > where "a" is a Form of rank 2 and "L" is a form of rank 1. Such as pde > will be treated as a linear variational problem. Some wild thoughts... Couldn't we just lump a and L into one form F, and let VariationalProblem then figure out what kindoff problem the user would like to solve? Basically VariationalProblem then solve F=0. Differentiate F if the form is of rank 1, (or take an optional Jacobian), or split it into a linear problem using lhs and rhs? > Philosophical question: Should u be given as an argument to the > VariationalProblem instead of to the call to solve? It is more natural to give u to solve, as that is what you solve for. Then you can differentiate wrt to u in the solve function. However, it makes it more difficult to make u an optional argument to solve. Johan > Comments welcome! > > -- > Marie > > > _______________________________________________ > Mailing list: https://launchpad.net/~dolfin > Post to : [email protected] > Unsubscribe : https://launchpad.net/~dolfin > More help : https://help.launchpad.net/ListHelp _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
