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Stash computed form on tensor for re-assembly #244

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Merged
kynan merged 3 commits into from
Apr 9, 2014
Merged

Stash computed form on tensor for re-assembly #244

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4e43d9f
Stash computed form on tensor for re-assembly
kynan Apr 8, 2014
2756719
Add test assembling different forms into the same Function
kynan Apr 8, 2014
856e76b
Add test assembling different forms into the same Matrix
kynan Apr 8, 2014
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12 changes: 11 additions & 1 deletion firedrake/solving.py
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Original file line number Diff line number Diff line change
Expand Up @@ -382,7 +382,17 @@ def _assemble(f, tensor=None, bcs=None):

"""

kernels = compile_form(f, "form")
# We stash the form and kernels on the tensor if we reassemble for an
# existing tensor, to save having to compile the form again if identical
# Note that forms override == to construct an equation, so we have to
# explicitly test for object identity
if getattr(tensor, "_form", None) is f and hasattr(tensor, "_kernels"):
kernels = tensor._kernels
else:
kernels = compile_form(f, "form")
if tensor:
tensor._form = f
tensor._kernels = kernels

@wence- wence- Apr 8, 2014

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Is this safe? I would have thought that we can use the same tensor to assemble a different form as long as the function spaces match. I think this means the following would fail:

v = TestFunction(V)

f = assemble(v*dx)

# do stuff with f

f = assemble(Constant(2)*v*dx, tensor=f)

Now the second time f is v_dx, not 2_v*dx

@wence- wence- Apr 8, 2014

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You could check by:

if blah and form is tensor._form:
   ...

I think

@kynan kynan Apr 8, 2014

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Isn't that exactly what I'm doing? Note that the check in line 389 is identical to this:

if hasattr(tensor, "_form") and hasattr(tensor, "_kernels") and tensor._form is f


fd = f.form_data()

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23 changes: 23 additions & 0 deletions tests/regression/test_assemble.py
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Expand Up @@ -66,6 +66,29 @@ def test_zero_form(M, f, one):
assert isinstance(zero_form, float)
assert abs(zero_form - 0.5 * np.prod(f.shape())) < 1.0e-12


def test_assemble_with_tensor(cg1):
v = TestFunction(cg1)
L = v*dx
f = Function(cg1)
# Assemble a form into f
f = assemble(L, f)
# Assemble a different form into f
f = assemble(Constant(2)*L, f)
# Make sure we get the result of the last assembly
assert np.allclose(f.dat.data, 2*assemble(L).dat.data, rtol=1e-14)


def test_assemble_mat_with_tensor(dg0):
u = TestFunction(dg0)
v = TrialFunction(dg0)
a = u*v*dx
M = assemble(a)
# Assemble a different form into M
M = assemble(Constant(2)*a, M)
# Make sure we get the result of the last assembly
assert np.allclose(M.M.values, 2*assemble(a).M.values, rtol=1e-14)

if __name__ == '__main__':
import os
pytest.main(os.path.abspath(__file__))