UFL

UFL#

DOLFINx 0.10 pins UFL 2025.2, 0.11 pins UFL 2026.1, and main uses UFL 2026.2.

fenicsx_compat.domain_of(expr) -> ufl.Mesh

The UFL domain of an expression. Raises ValueError unless there is exactly one.

DOLFINx	Native
0.10, 0.11, main	`ufl.domain.extract_domains(expr)`, which returns all domains, or `ufl.domain.extract_unique_domain(expr)`, which returns `None` if there is none

domain = fenicsx_compat.domain_of(u)

It does not depend on the version. It is a shorthand that also checks that there is exactly one domain.

fenicsx_compat.apply_pullback_inverse(pullback, expr, domain) -> ufl.core.expr.Expr

Maps an expression on the physical cell to the reference cell, by inverting the element’s pull back.

DOLFINx (UFL)	Native
0.10 (2025.2), 0.11 (2026.1)	None. Closed forms are used here for the identity (`u`), contravariant Piola (`det(J) K u`) and covariant Piola (`J^T u`) pull backs. Other pull backs raise `NotImplementedError`.
main (2026.2, UFL PR #511)	`pullback.apply_inverse(expr, domain)`

v = ufl.TestFunction(V)
v_ref = fenicsx_compat.apply_pullback_inverse(V.ufl_element().pullback, v, mesh.ufl_domain())

The Piola closed forms assume a vector-valued expression, which is what Piola-mapped elements have.