dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Thursday 12 March 2009 09:37:58 Anders Logg wrote:
> On Wed, Mar 11, 2009 at 11:15:44PM +0100, Anders Logg wrote:
> > On Wed, Mar 11, 2009 at 11:01:56PM +0100, DOLFIN wrote:
> > > One or more new changesets pushed to the primary dolfin repository.
> > > A short summary of the last three changesets is included below.
> > >
> > > changeset:   5853:f1ef6132a568d5a56e5c70b17ce118c19bfa961c
> > > tag:         tip
> > > user:        Anders Logg <logg@xxxxxxxxx>
> > > date:        Wed Mar 11 23:01:49 2009 +0100
> > > files:       ChangeLog demo/pde/poisson/cpp/Poisson.h
> > > dolfin/function/Function.cpp sandbox/misc/Poisson.form
> > > sandbox/misc/Poisson.h sandbox/misc/README sandbox/misc/SConstruct
> > > sandbox/misc/cpp/Poisson.form sandbox/misc/cpp/Poisson.h
> > > sandbox/misc/cpp/SConstruct sandbox/misc/cpp/main.cpp
> > > sandbox/misc/main.cpp description:
> > > Automatically interpolate user-defined functions on assignment
> >
> > This is something we discussed a while back but we didn't agree on
> > whether or not it was a good idea. I think it is and it's easy enough
> > to remove if there is strong enough pressure against it.
> >
> > Here are two examples of assignment:
> >
> > Case 1: Time-stepping with user-defined initial data
> >
> >     # Initializations
> >     mesh = UnitSquare(32, 32)
> >     V = FunctionSpace(mesh, "Lagrange", 1)
> >     u0 = Function(V, "sin(x[0])")
> >     u1 = Function(V)
> >
> >     # Time stepping
> >     for i in range(10):
> >
> >         print i
> >
> >         # Solve for u1
> >         u1.vector()
> >
> >         # Assign u0 = u1
> >         u0.assign(u1)
> >
> >
> > This works fine since u1 is defined by a vector of dofs so the
> > assignment is allowed.
> >
> > Case 2: Time-stepping with user-defined coefficient
> >
> >     # Initializations
> >     mesh = UnitSquare(32, 32)
> >     V = FunctionSpace(mesh, "Lagrange", 1)
> >     w0 = Function(V)
> >     w1 = Function(V, "sin(t*x[0])")
> >
> >     # Time stepping
> >     for i in range(10):
> >
> >         print i
> >
> >         # Update w1
> >         w1.t = float(i)
> >
> >         # Solve for u
> >
> >         # Assign w0 = w1 (does not work)
> >         w0.assign(w1)
> >         #w0 = interpolate(w1, V)
> >         #w0 = project(w1, V)
> >
> > This breaks since assignment is not allowed from the user-defined
> > Function w1. Interpolation or projection helps, but each of these
> > return a new function, which will confuse the JIT compiler (at least
> > the current FFC JIT compiler) and lead to excessive generation of code
> > (no cache reuse).
> >
> > The new version of the assignment operator allows this kind of
> > assignment and automatically interpolates when necessary. It also
> > prints out the following message:
> >
> >   Assignment from user-defined function, interpolating.
> >
> > So it should be clear what happens. Any objections?
>
> Any more thoughts on this?

Fine with me. 

Could you add some unit tests for this?

Johan