dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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?

-- 
Anders

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