dolfin team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

I checked out what UFL does. If you look at expand_indices.py,
you see that this algorithm does handle symmetries. However,
that algorithm is not (and should not be) used by all form compiler
variants. Here's a simplified version of the code:

    def form_argument(self, x):
        if x.shape() == ():
            return x
        else:
            e = x.element()

            # Get component
            c = self.component()

            # Map it through the symmetry mapping
            if isinstance(e, TensorElement):
                s = e.symmetry() or {}
                c = s.get(c, c)

            return x[c]


I want to make two points from this code:

1) The symmetry mapping is currently only available directly from a
TensorElement. Extending symmetries to be a property of all ufl
expressions could be quite a bit of work. If this is a wanted feature,
make a blueprint.

2) When you do have the symmetry mapping at hand, the mapping is
trivial. It should be a quick fix in FFC, just apply the symmetry
mapping like above everywhere you get the component of a form
argument.

Martin

2011/4/5 Kristian B. Ølgaard <745646@xxxxxxxxxxxxxxxxxx>:
> The following simple form also fails:
>
> T1 = TensorElement('CG', triangle, 1, symmetry=True)
> T2 = TensorElement('CG', triangle, 1, symmetry=True)
> TT = T1*T2
> P, Q = Coefficients(TT)
> M = inner(P, Q)*dx
> print M
>
> Printing 'M' results in:
>
> { ([[
>  [ (w_0)[0], (w_0)[1] ],
>  [ (w_0)[1], (w_0)[3] ]
> ]]) : ([[
>  [ (w_0)[4], (w_0)[5] ],
>  [ (w_0)[5], (w_0)[7] ]
> ]]) } * dx0
>
> which illustrates the problem in FFC for both tensor and quadrature representations.
> The component '7' in the ListTensor does not exist in the MixedElement of FFC which, due to symmetry, only contain 6 'unique' subelements (components).
> One could argue that UFL should keep track of symmetry when creating the indices of list tensors such that it maps 3->2, 4->3, 5->4 and 7->6.
>
> --
> You received this bug notification because you are a member of DOLFIN
> Team, which is subscribed to DOLFIN.
> https://bugs.launchpad.net/bugs/745646
>
> Title:
>  Problem with assemble() with MixedFunctionSpace of symmetric
>  TensorFunctionSpaces
>
> Status in DOLFIN:
>  New
>
> Bug description:
>  from dolfin import *
>
>  mesh = Rectangle(0,0,1,1,10,10)
>  dim = 2 #assume 2D
>  symm = dict(((i,j), (j,i))
>              for i in range(dim) for j in range(dim) if i > j )
>
>  T1 = TensorFunctionSpace(mesh, 'CG', 1, symmetry=symm)
>  T2 = TensorFunctionSpace(mesh, 'CG', 1, symmetry=symm)
>
>  TT = T1*T2
>
>  R, S = TrialFunctions(TT)
>  v_R, v_S = TestFunctions(TT)
>
>  P = Function(T1)
>  Q = Function(T2)
>
>  Fr = inner(R,v_R)*dx+ inner(P,v_R)*dx
>
>  Fs = inner( S, v_S )*dx + inner( Q, v_S )*dx
>
>  F = Fr + Fs
>
>  A = lhs(F)
>  B = rhs(F)
>
>  a = Matrix()
>  a = assemble(A, tensor=a)
>  b = Vector()
>  b = assemble(B, tensor=b)
>
>  I get the following error:
>
>  Calling FFC just-in-time (JIT) compiler, this may take some time.
>  Traceback (most recent call last):
>    File "tensortest2.py", line 28, in <module>
>      a = assemble(A, tensor=a)
>    File "/usr/lib/python2.6/dist-packages/dolfin/fem/assemble.py", line 100, in assemble
>      common_cell=common_cell)
>    File "/usr/lib/python2.6/dist-packages/dolfin/fem/form.py", line 34, in __init__
>      (self._compiled_form, module, self.form_data) = jit(form, form_compiler_parameters, common_cell)
>    File "/usr/lib/python2.6/dist-packages/dolfin/compilemodules/jit.py", line 47, in mpi_jit
>      return local_jit(*args, **kwargs)
>    File "/usr/lib/python2.6/dist-packages/dolfin/compilemodules/jit.py", line 114, in jit
>      return jit_compile(form, parameters=p, common_cell=common_cell)
>    File "/usr/lib/python2.6/dist-packages/ffc/jitcompiler.py", line 64, in jit
>      return jit_form(object, parameters, common_cell)
>    File "/usr/lib/python2.6/dist-packages/ffc/jitcompiler.py", line 122, in jit_form
>      compile_form(preprocessed_form, prefix=jit_object.signature(), parameters=parameters)
>    File "/usr/lib/python2.6/dist-packages/ffc/compiler.py", line 140, in compile_form
>      ir = compute_ir(analysis, parameters)
>    File "/usr/lib/python2.6/dist-packages/ffc/representation.py", line 66, in compute_ir
>      irs = [_compute_integral_ir(f, i, parameters) for (i, f) in enumerate(forms)]
>    File "/usr/lib/python2.6/dist-packages/ffc/representation.py", line 186, in _compute_integral_ir
>      parameters)
>    File "/usr/lib/python2.6/dist-packages/ffc/tensor/tensorrepresentation.py", line 59, in compute_integral_ir
>      ir["AK"] = _compute_terms(monomial_form, None, None, domain_type, quadrature_degree)
>    File "/usr/lib/python2.6/dist-packages/ffc/tensor/tensorrepresentation.py", line 98, in _compute_terms
>      quadrature_degree)
>    File "/usr/lib/python2.6/dist-packages/ffc/tensor/referencetensor.py", line 28, in __init__
>      self.A0 = integrate(monomial, domain_type, facet0, facet1, quadrature_order)
>    File "/usr/lib/python2.6/dist-packages/ffc/tensor/monomialintegration.py", line 50, in integrate
>      psis = [_compute_psi(v, table, len(points), domain_type) for v in monomial.arguments]
>    File "/usr/lib/python2.6/dist-packages/ffc/tensor/monomialintegration.py", line 169, in _compute_psi
>      Psi[component][tuple(dlist)] = etable[dtuple][:, cindex[0].index_range[component], :]
>
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