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Use interpolate rather than project for creating legacy data #75

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Merged
finsberg merged 1 commit into from
Sep 3, 2026
Merged

Use interpolate rather than project for creating legacy data #75

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16 changes: 7 additions & 9 deletions tests/create_legacy_data.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,15 +28,13 @@ def create_reference_data(
mesh = dolfin.UnitCubeMesh(1, 1, 1)
V = dolfin.FunctionSpace(mesh, family, degree)
W = dolfin.VectorFunctionSpace(mesh, family, degree)
x = dolfin.SpatialCoordinate(mesh)

# NOTE: f0 must be exactly representable in the (family, degree) function space above.
# Legacy dolfin (FIAT-based quadrature) and current dolfinx (basix-based quadrature)
# use different quadrature rules, so a non-polynomial (e.g. conditional) integrand
# would project to slightly different values in each toolchain, making bit-exact
# comparisons in test_legacy_readers.py inherently flaky across dolfinx versions.
f0 = x[0] ** 2 + 2 * x[1] * x[2] - x[1]
v0 = dolfin.project(f0, V)

# NOTE: f0 must be exactly representable in the (family, degree) function space above,
# and written via interpolation (not dolfin.project, which goes through a linear solve
# and does not reproduce exact nodal values here) so that comparisons against a fresh
# dolfinx solve/interpolation in test_legacy_readers.py are not sensitive to quadrature
# or solver differences between legacy dolfin and current dolfinx.
v0 = dolfin.interpolate(dolfin.Expression("x[0]*x[0] + 2*x[1]*x[2] - x[1]", degree=2), V)
w0 = dolfin.interpolate(dolfin.Expression(("x[0]", "3*x[2]", "7*x[1]"), degree=1), W)

v1 = dolfin.interpolate(dolfin.Expression("x[0]", degree=1), V)
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