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FEniCS / ufl

UFL - Unified Form Language
https://fenicsproject.org
GNU Lesser General Public License v3.0
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Handling of extract_blocks when part is equal to zero. #285

Closed jorgensd closed 3 months ago

jorgensd commented 3 months ago

Resolve #284

jorgensd commented 3 months ago

Current basix/ffcx/ufl example:

import basix.ufl
import ufl

cell = "triangle"
c_el = basix.ufl.element("Lagrange", cell,1, shape=(2, ))
mesh = ufl.Mesh(c_el)

element = basix.ufl.element("Lagrange", cell, 1)
me = basix.ufl.mixed_element([element, element])
W = ufl.FunctionSpace(mesh, me)
v,q = ufl.TestFunctions(W)

F = v*ufl.dx  + q.dx(0)*ufl.dx
F0 = ufl.extract_blocks(F,0)
F1 = ufl.extract_blocks(F,1)

u, p = ufl.TrialFunctions(W)
J = ufl.inner(u, v)*ufl.dx + p*v.dx(0)*ufl.dx + q*u.dx(0)*ufl.dx + ufl.inner(ufl.grad(p), ufl.grad(q))*ufl.dx
J00 = ufl.extract_blocks(J,0,0)
J01 = ufl.extract_blocks(J,0,1)
J10 = ufl.extract_blocks(J,1,0)
J11 = ufl.extract_blocks(J,1,1)

forms = [F0, F1]