From 4e43d9fe212bce90d9da3ccb208e006671105abd Mon Sep 17 00:00:00 2001
From: Florian Rathgeber <florian.rathgeber@gmail.com>
Date: Tue, 8 Apr 2014 18:50:45 +0100
Subject: [PATCH 1/3] Stash computed form on tensor for re-assembly

When passing in a tensor to assemble, stash the form and computed
kernels on the tensor such that if we reassemble the same form on
the same tensor we save having to preprocess/split the form again.
---
 firedrake/solving.py | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/firedrake/solving.py b/firedrake/solving.py
index 8a86ac96b1..62c32c1a7a 100644
--- a/firedrake/solving.py
+++ b/firedrake/solving.py
@@ -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
 
     fd = f.form_data()
 

From 275671906283fa0a570b87261987adaa9541220f Mon Sep 17 00:00:00 2001
From: Florian Rathgeber <florian.rathgeber@gmail.com>
Date: Tue, 8 Apr 2014 21:55:38 +0100
Subject: [PATCH 2/3] Add test assembling different forms into the same
 Function

---
 tests/regression/test_assemble.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/regression/test_assemble.py b/tests/regression/test_assemble.py
index 8cac2b4e7a..192334904a 100644
--- a/tests/regression/test_assemble.py
+++ b/tests/regression/test_assemble.py
@@ -66,6 +66,18 @@ 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)
+
 if __name__ == '__main__':
     import os
     pytest.main(os.path.abspath(__file__))

From 856e76b211b7369d2dca5310a07807ffd4c38e1e Mon Sep 17 00:00:00 2001
From: Florian Rathgeber <florian.rathgeber@gmail.com>
Date: Tue, 8 Apr 2014 21:55:49 +0100
Subject: [PATCH 3/3] Add test assembling different forms into the same Matrix

---
 tests/regression/test_assemble.py | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/regression/test_assemble.py b/tests/regression/test_assemble.py
index 192334904a..0ca9e191bb 100644
--- a/tests/regression/test_assemble.py
+++ b/tests/regression/test_assemble.py
@@ -78,6 +78,17 @@ def test_assemble_with_tensor(cg1):
     # 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__))