The two forms generates the same signature, but different
tabulate_tensor functions. Something is fishy with form_data.signature.

instant-clean
run script
out-comment region and run instant-clean

from dolfin import *

mesh = UnitSquareMesh(16,16)
V = FunctionSpace(mesh, 'CG', 2)
w = TestFunction(V)
Pv = TrialFunction(V)
a = inner(w, Pv)*dx
A = assemble(a)
u = Function(V)

# Out-comment next region and run instant clean to reproduce bug
f = Expression("x[0]*x[0] + 2*x[1]*x[1]")
L = inner(w, f)*dx
b = assemble(L)
print "Signature", L.form_data().signature
solve(A, u.vector(), b)
print u.vector().norm("l2")
# Out-comment to here.

f2 = Expression("x[0]*x[0] + 2*x[1]*x[1]", degree=2)
L = inner(w, f2)*dx
b = assemble(L)
solve(A, u.vector(), b)
print "Signature", L.form_data().signature
print u.vector().norm("l2")


Happy bug hunting :)

Johan


On 03/11/2013 07:28 PM, Martin Sandve Alnæs wrote:
> I would look at the instant side. Or in ffc.jitobject. repr of a form is
> not used anywhere.
> 
> Martin
> Den 11. mars 2013 18:20 skrev "Johan Hake" <email address hidden>
> følgende:
> 
>> On 03/11/2013 04:31 PM, Marie Rognes wrote:
>>> On 03/11/2013 04:07 PM, Johan Hake wrote:
>>>> Are you sure this is a bug?
>>>
>>> Pretty sure, yes.
>>>
>>>> In the first example the Expression is generated without setting the
>>>> degree. If this is auto chosen to 2 it should make perfectly sense they
>>>> give the same results.
>>>
>>> Yes. But the problem is that the Expression with degree=2 gives
>>> different results depending on what has been compiled before it.
>>>
>>>> Change degree to something else and you will have
>>>> a different results.
>>>
>>> Did you read the problem carefully? Look at (*) and (**).  Both of these
>>> correspond to setting degree=2 explicitly. The numbers should therefore
>>> be the same. They are not, which is highly disturbing. (*) is produced
>>> after doing instant-clean, running with auto degree, and running with
>>> degree = 2 (which seems to reuse the auto degree code); while (**) is
>>> produced after doing instant-clean and directly running with degree=2.
>>
>> Ok, I see it now. Pretty disturbing yes.
>>
>> How can we find out what degree is chosen for the expression when it is
>> autogenerated? Is it during preprocess? Is it still so that it is the
>> repr of the preprocessed form that determines if a form will get
>> recompiled?
>>
>> from dolfin import *
>>
>> mesh = UnitSquareMesh(16,16)
>> V = FunctionSpace(mesh, 'CG', 2)
>> w = TestFunction(V)
>> f = Expression("x[0]*x[0] + 2*x[1]*x[1]")
>> L = inner(w, f)*dx
>> b = assemble(L)
>>
>> print "Preprocessed:", repr(L.form_data().preprocessed_form)
>> print "Not preprocessed:", repr(L)
>>
>> Prints:
>> Preprocessed: Form([Integral(Product(Argument(FiniteElement('Lagrange',
>> Domain(Cell('triangle', 2), 'triangle_multiverse', 2, 2), 2, None), -2),
>> Coefficient(FiniteElement('Lagrange', None, None, None), 0)), 'cell',
>> 'otherwise', None, None)])
>> Not preprocessed:
>> Form([Integral(Product(Argument(FiniteElement('Lagrange',
>> Domain(Cell('triangle', 2), 'triangle_multiverse', 2, 2), 2, None), -2),
>> Coefficient(FiniteElement('Lagrange', None, None, None), 0)), 'cell',
>> 'everywhere', None, None)])
>>
>> Where it is clear that the Coefficient of the first form has not got any
>> degree. Shouldn't it have got one?
>>
>> Johan
>>
>>
>>> --
>>> Marie
>>>
>>>
>>>> Johan
>>>>
>>>> On 03/11/2013 10:06 AM, Marie Rognes wrote:
>>>>> Public bug reported:
>>>>>
>>>>> There seems to be something seriously wrong with either DOLFIN-FFC jit
>>>>> compilation or caching or instant.
>>>>>
>>>>> To reproduce, for instance consider the following code snippet and do
>>>>> the following
>>>>>
>>>>> (1): Run instant-clean
>>>>>
>>>>> (2): Run script unmodified.
>>>>>
>>>>> Output is:
>>>>>
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Calling DOLFIN just-in-time (JIT) compiler, this may take some time.
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>>>> 40.4757877531
>>>>>
>>>>> (3) Uncomment commented lines and run.
>>>>>
>>>>> Output is:
>>>>>
>>>>> Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>>>> 40.4757877531
>>>>> Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>>>> 40.4757877531 (*)
>>>>>
>>>>> (4) Run instant-clean, comment out lines defining f, g, and 1st print.
>>>>> Run.
>>>>>
>>>>> Output is
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Calling DOLFIN just-in-time (JIT) compiler, this may take some time.
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Calling FFC just-in-time (JIT) compiler, this may take some time.
>>>>> Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>>>> 40.490263582 (**)
>>>>>
>>>>> Problem: The last two floats, tagged by (*) and (**), should be the
>>>>> same: they are not.
>>>>>
>>>>> Code snippet:
>>>>>
>>>>> --
>>>>>
>>>>>
>>>>> from dolfin import *
>>>>> mesh = UnitSquareMesh(16,16)
>>>>> V = FunctionSpace(mesh, 'CG', 2)
>>>>>
>>>>> f = Expression("x[0]*x[0] + 2*x[1]*x[1]")
>>>>> g = project(f, V)
>>>>> print g.vector().norm("l2")
>>>>>
>>>>> #f2 = Expression("x[0]*x[0] + 2*x[1]*x[1]", degree=2)
>>>>> #g2 = project(f2, V)
>>>>> #print g2.vector().norm("l2")
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> ** Affects: dolfin
>>>>>       Importance: Undecided
>>>>>           Status: New
>>>>>
>>>
>>
>> --
>> You received this bug notification because you are a member of DOLFIN
>> Core Team, which is subscribed to DOLFIN.
>> https://bugs.launchpad.net/bugs/1153508
>>
>> Title:
>>   Strange results in JIT compilation
>>
>> Status in DOLFIN:
>>   Confirmed
>>
>> Bug description:
>>   There seems to be something seriously wrong with either DOLFIN-FFC jit
>>   compilation or caching or instant.
>>
>>   To reproduce, for instance consider the following code snippet and do
>>   the following
>>
>>   (1): Run instant-clean
>>
>>   (2): Run script unmodified.
>>
>>   Output is:
>>
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Calling DOLFIN just-in-time (JIT) compiler, this may take some time.
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>   40.4757877531
>>
>>   (3) Uncomment commented lines and run.
>>
>>   Output is:
>>
>>   Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>   40.4757877531
>>   Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>   40.4757877531 (*)
>>
>>   (4) Run instant-clean, comment out lines defining f, g, and 1st print.
>>   Run.
>>
>>   Output is
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Calling DOLFIN just-in-time (JIT) compiler, this may take some time.
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Calling FFC just-in-time (JIT) compiler, this may take some time.
>>   Solving linear system of size 1089 x 1089 (PETSc Krylov solver).
>>   40.490263582 (**)
>>
>>   Problem: The last two floats, tagged by (*) and (**), should be the
>>   same: they are not.
>>
>>   Code snippet:
>>
>>   --
>>
>>
>>   from dolfin import *
>>   mesh = UnitSquareMesh(16,16)
>>   V = FunctionSpace(mesh, 'CG', 2)
>>
>>   f = Expression("x[0]*x[0] + 2*x[1]*x[1]")
>>   g = project(f, V)
>>   print g.vector().norm("l2")
>>
>>   #f2 = Expression("x[0]*x[0] + 2*x[1]*x[1]", degree=2)
>>   #g2 = project(f2, V)
>>   #print g2.vector().norm("l2")
>>
>>
>>   --
>>
>> To manage notifications about this bug go to:
>> https://bugs.launchpad.net/dolfin/+bug/1153508/+subscriptions
>>
>