Allow Christiansen-Hu in 2D

FIAT/christiansen_hu.py

@@ -12,7 +12,6 @@
 from FIAT import finite_element, polynomial_set
 from FIAT.bernardi_raugel import BernardiRaugelDualSet
 from FIAT.quadrature_schemes import create_quadrature
-from FIAT.reference_element import TETRAHEDRON
 from FIAT.macro import CkPolynomialSet, WorseyFarinSplit
 
 import numpy
@@ -70,8 +69,6 @@ class ChristiansenHu(finite_element.CiarletElement):
  """The Christiansen-Hu C^0(Worsey-Farin) linear macroelement with divergence in P0.
  This element belongs to a Stokes complex, and is paired with unsplit DG0."""
  def __init__(self, ref_el, degree=1):
- if ref_el.get_shape() != TETRAHEDRON:
- raise ValueError("Christiansen-Hu only defined on tetrahedra")
  if degree != 1:
  raise ValueError("Christiansen-Hu only defined for degree = 1")
  poly_set = ChristiansenHuSpace(ref_el, degree)

test/unit/test_fiat.py

@@ -319,6 +319,7 @@ def __init__(self, a, b):
  "AlfeldSorokina(T)",
  "AlfeldSorokina(S)",
  "ArnoldQin(T)",
+ "ChristiansenHu(T)",
  "ChristiansenHu(S)",
  "GuzmanNeilan(T)",
  "GuzmanNeilan(S)",

test/unit/test_macro.py

@@ -383,7 +383,7 @@ def test_AlfeldSorokinaSpace(cell, degree):
  assert numpy.allclose(residual, 0)
 
 
-@pytest.mark.parametrize("family", ("CH", "GN"))
+@pytest.mark.parametrize("family", ("AQ", "CH", "GN"))
 def test_minimal_stokes_space(cell, family):
  # Test that the C0 Stokes space is spanned by a C0 basis
  # Also test that its divergence is constant
@@ -396,12 +396,14 @@ def test_minimal_stokes_space(cell, family):
  if family == "GN":
  degree = sd
  space = ExtendedGuzmanNeilanSpace
- elif sd == 2:
- degree = 2
- space = ArnoldQinSpace
- elif sd == 3:
+ elif family == "CH":
  degree = 1
  space = ChristiansenHuSpace
+ elif family == "AQ":
+ if sd != 2:
+ return
+ degree = 2
+ space = ArnoldQinSpace
 
  W = space(cell, degree)
  V = space(cell, degree, reduced=True)