UFLACS generates undefined variable for quadrature element

[Umberto Villa]

UFLACS generates a code with undefined variable FE6_C0_Q3

element = FiniteElement("Quadrature", triangle, 2, quad_scheme="default")
p = TrialFunction(element)
q = TestFunction(element)
a = p*q*dx(degree=2)

Other representations work fine.

[Umberto Villa]

Hi Jan,

Thanks for editing my report and for pointing out that other representations work fine.

Following your suggestion, I was able to work around this issue by changing the representation to quadrature for this variational form only (and then switching it back to uflacs for the other weak forms).

Best,

Umberto

[Jan Blechta]

Issue #171 was marked as a duplicate of this issue.

[Marco Morandini]

A workaround for UFLACS is

--- a/ffc/uflacs/build_uflacs_ir.py
+++ b/ffc/uflacs/build_uflacs_ir.py
@@ -697,7 +697,7 @@ def build_uflacs_ir(cell, integral_type, entitytype,

         # Drop tables not referenced from modified terminals
         # and tables of zeros and ones
-        unused_ttypes = ("zeros", "ones", "quadrature")
+        unused_ttypes = ("zeros", "ones")
         keep_table_names = set()
         for name in active_table_names:
             ttype = ir["unique_table_types"][name]

With the above patch it should work, and I do not see any increase of computational time wrt. the quadrature representation. It is likely that the c++ compiler detects that variables like FE6_C0_Q3 are either == 1. or == 0. and simplifies the generated code accordingly.

The best fix would be to implement separate block modes for quadrature arguments, as already hinted in build_uflacs_ir.py:

            # TODO: Add separate block modes for quadrature
            # Both arguments in quadrature elements
            """
            for iq
                fw = f*w
                #for i
                #    for j
                #        B[i,j] = fw*U[i]*V[j] = 0 if i != iq or j != iq
                BQ[iq] = B[iq,iq] = fw
            for (iq) 
                A[iq+offset0, iq+offset1] = BQ[iq]
            """
            # One argument in quadrature element
            """
            for iq
                fw[iq] = f*w
                #for i
                #    for j
                #        B[i,j] = fw*UQ[i]*V[j] = 0 if i != iq
                for j
                    BQ[iq,j] = fw[iq]*V[iq,j]
            for (iq) for (j)
                A[iq+offset, j+offset] = BQ[iq,j]
            """

@blechta , what should we do?

[Umberto Villa]

This error with uflacs is still present in 2017.2.0.

If I manually set ' parameters["form_compiler"]["representation"] = "quadrature" ', how can I silence this warning?

/usr/local/lib/python2.7/dist-packages/ffc/jitcompiler.py:235: QuadratureRepresentationDeprecationWarning: 
*** ===================================================== ***
*** FFC: quadrature representation is deprecated! It will ***
*** likely be removed in 2018.1.0 release. Use uflacs     ***
*** representation instead.                               ***
*** ===================================================== ***
  issue_deprecation_warning()

[Jan Blechta]

Silence the warning this way

import warnings
from ffc.quadrature.deprecation import QuadratureRepresentationDeprecationWarning
warnings.simplefilter("once", QuadratureRepresentationDeprecationWarning)

if you really need to.

[Jan Blechta]

This issues blocks removing the quadrature representation.