test assembly of composition of interpolates (#4710)

Author: leo-collins

tests/firedrake/regression/test_interpolate.py

@@ -620,3 +620,42 @@ def test_mixed_space_bcs():
     expected = assemble(interpolate(sum(w), V), bcs=bcs[-1:])
 
     assert np.allclose(result.dat.data, expected.dat.data)
+
+
+@pytest.mark.parallel([1, 3])
+@pytest.mark.parametrize("mode", ["forward", "adjoint"])
+def test_interpolate_composition(mode):
+    mesh = UnitSquareMesh(4, 4)
+    x, y = SpatialCoordinate(mesh)
+
+    V5 = FunctionSpace(mesh, "CG", 5)
+    V4 = FunctionSpace(mesh, "CG", 4)
+    V3 = FunctionSpace(mesh, "CG", 3)
+    V2 = FunctionSpace(mesh, "CG", 2)
+    V1 = FunctionSpace(mesh, "CG", 1)
+
+    if mode == "forward":
+        u5 = Function(V5).interpolate(sin(x + y))
+        u4 = interpolate(u5, V4)
+        u3 = interpolate(u4, V3)
+        u2 = interpolate(u3, V2)
+        u1 = interpolate(u2, V1)
+
+        assert u1.function_space() == V1
+
+        res = assemble(u1)
+        res2 = assemble(interpolate(sin(x + y), V1))
+        assert np.allclose(res.dat.data_ro, res2.dat.data_ro)
+
+    if mode == "adjoint":
+        u1 = conj(TestFunction(V1)) * dx
+        u2 = interpolate(TestFunction(V2), u1)
+        u3 = interpolate(TestFunction(V3), u2)
+        u4 = interpolate(TestFunction(V4), u3)
+        u5 = interpolate(TestFunction(V5), u4)
+
+        assert u5.function_space() == V5.dual()
+
+        res_adj = assemble(u5)
+        res_adj2 = assemble(interpolate(TestFunction(V5), conj(TestFunction(V1)) * dx))
+        assert np.allclose(res_adj.dat.data_ro, res_adj2.dat.data_ro)