replace fails for Indexed Coefficients

[Johan Hake]

This code:

from ufl import *
fe = FiniteElement("CG", triangle, 1)*FiniteElement("CG", triangle, 1)
u0, u1 = Coefficients(fe)
replace(u0*dx ,{u0:u1})

triggers an assertion:
UFLException: This implementation can only replace Terminal objects.

[Martin Sandve Alnæs (martinal)]

Hm. I'm not sure how safe replace of non-terminal objects would be in general, so I don't want to go there.

But in this particular case, replacing an indexed of a coefficient, it should be feasible and safe to fix.

[Martin Sandve Alnæs (martinal)]

Actually, no. It is too messy. The problem is this:

V = VectorElement(...)
f = Coefficient(V)
u, v = split(f)
M = u*v*f*dx
M2 = replace(M, { u: v })

What does this mean? Replacing terminals is rather unambiguous, this is not.

If you instead do:

from ufl import *
fe = VectorElement("CG", triangle, 1)
f = Coefficient(fe)
u0, u1 = split(f)
f2 = as_vector((u1, u1))
print str(replace(u0*dx, {f: f2}))

you should hopefully get what you need.

The alternative would be something much more intelligent than replace.

[Johan Hake (johan-hake)]

On Friday October 21 2011 07:47:34 Martin Sandve Alnæs wrote:
> Actually, no. It is too messy. The problem is this:
>
> V = VectorElement(...)
> f = Coefficient(V)
> u, v = split(f)
> M = u*v*f*dx
> M2 = replace(M, { u: v })
>
> What does this mean? Replacing terminals is rather unambiguous, this is
> not.

Ok.

> If you instead do:
>
> from ufl import *
> fe = VectorElement("CG", triangle, 1)
> f = Coefficient(fe)
> u0, u1 = split(f)
> f2 = as_vector((u1, u1))
> print str(replace(u0*dx, {f: f2}))
>
> you should hopefully get what you need.

Nice workaround!

> The alternative would be something much more intelligent than replace.

Ok, can you just enlight me why the result from as_vector is a terminal
object, and the result from a split is not.

> ** Changed in: ufl
> Status: Confirmed => Won't Fix

Ok

Johan

[Martin Sandve Alnæs (martinal)]

It is not, it is the key (f) that has to be a terminal.

Martin

Den 21. okt. 2011 kl. 18:01 skrev Johan Hake <email address hidden>:

> On Friday October 21 2011 07:47:34 Martin Sandve Alnæs wrote:
>> Actually, no. It is too messy. The problem is this:
>>
>> V = VectorElement(...)
>> f = Coefficient(V)
>> u, v = split(f)
>> M = u*v*f*dx
>> M2 = replace(M, { u: v })
>>
>> What does this mean? Replacing terminals is rather unambiguous, this is
>> not.
>
> Ok.
>
>> If you instead do:
>>
>> from ufl import *
>> fe = VectorElement("CG", triangle, 1)
>> f = Coefficient(fe)
>> u0, u1 = split(f)
>> f2 = as_vector((u1, u1))
>> print str(replace(u0*dx, {f: f2}))
>>
>> you should hopefully get what you need.
>
> Nice workaround!
>
>> The alternative would be something much more intelligent than replace.
>
> Ok, can you just enlight me why the result from as_vector is a terminal
> object, and the result from a split is not.
>
>> ** Changed in: ufl
>> Status: Confirmed => Won't Fix
>
> Ok
>
> Johan
>
> --
> You received this bug notification because you are subscribed to FEniCS
> Project.
> https://bugs.launchpad.net/bugs/875279
>
> Title:
> replace fails for Indexed Coefficients
>
> Status in Unified Form Language:
> Won't Fix
>
> Bug description:
> This code:
>
> from ufl import *
> fe = FiniteElement("CG", triangle, 1)*FiniteElement("CG", triangle, 1)
> u0, u1 = Coefficients(fe)
> replace(u0*dx ,{u0:u1})
>
> triggers an assertion:
> UFLException: This implementation can only replace Terminal objects.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ufl/+bug/875279/+subscriptions

[Johan Hake (johan-hake)]

On Friday October 21 2011 10:02:56 Martin Sandve Alnæs wrote:
> It is not, it is the key (f) that has to be a terminal.

Ahhh, slowly getting there!

Johan

> Martin
>
> Den 21. okt. 2011 kl. 18:01 skrev Johan Hake
>
> <email address hidden>:
> > On Friday October 21 2011 07:47:34 Martin Sandve Alnæs wrote:
> >> Actually, no. It is too messy. The problem is this:
> >>
> >> V = VectorElement(...)
> >> f = Coefficient(V)
> >> u, v = split(f)
> >> M = u*v*f*dx
> >> M2 = replace(M, { u: v })
> >>
> >> What does this mean? Replacing terminals is rather unambiguous, this is
> >> not.
> >
> > Ok.
> >
> >> If you instead do:
> >>
> >> from ufl import *
> >> fe = VectorElement("CG", triangle, 1)
> >> f = Coefficient(fe)
> >> u0, u1 = split(f)
> >> f2 = as_vector((u1, u1))
> >> print str(replace(u0*dx, {f: f2}))
> >>
> >> you should hopefully get what you need.
> >
> > Nice workaround!
> >
> >> The alternative would be something much more intelligent than replace.
> >
> > Ok, can you just enlight me why the result from as_vector is a terminal
> > object, and the result from a split is not.
> >
> >> ** Changed in: ufl
> >>
> >> Status: Confirmed => Won't Fix
> >
> > Ok
> >
> > Johan