dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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?

-- 
Anders

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