#741 coverage

Author: rtimms

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Features
 
+-   Changed finite volume discretisation to use exact values provided by Neumann boundary conditions when computing the gradient ([#748](https://github.com/pybamm-team/PyBaMM/pull/748))
 -   Generalized importing of external variables ([#728](https://github.com/pybamm-team/PyBaMM/pull/728))
 -   Separated active and inactive material volume fractions ([#726](https://github.com/pybamm-team/PyBaMM/pull/726))
 -   Added submodels for tortuosity ([#726](https://github.com/pybamm-team/PyBaMM/pull/726))

pybamm/spatial_methods/finite_volume.py

@@ -71,10 +71,11 @@ def gradient(self, symbol, discretised_symbol, boundary_conditions):
         # Add Dirichlet boundary conditions, if defined
         if symbol.id in boundary_conditions:
             bcs = boundary_conditions[symbol.id]
-            # add ghost nodes and update domain
-            discretised_symbol, domain = self.add_ghost_nodes(
-                symbol, discretised_symbol, bcs
-            )
+            if any(bc[1] == "Dirichlet" for bc in bcs.values()):
+                # add ghost nodes and update domain
+                discretised_symbol, domain = self.add_ghost_nodes(
+                    symbol, discretised_symbol, bcs
+                )
 
         # note in 1D spherical grad and normal grad are the same
         gradient_matrix = self.gradient_matrix(domain)
@@ -85,7 +86,8 @@ def gradient(self, symbol, discretised_symbol, boundary_conditions):
         # Add Neumann boundary conditions, if defined
         if symbol.id in boundary_conditions:
             bcs = boundary_conditions[symbol.id]
-            out = self.add_neumann_values(symbol, out, bcs, domain)
+            if any(bc[1] == "Neumann" for bc in bcs.values()):
+                out = self.add_neumann_values(symbol, out, bcs, domain)
 
         return out
 

tests/unit/test_spatial_methods/test_finite_volume/test_finite_volume.py

@@ -89,6 +89,7 @@ def test_discretise_diffusivity_times_spatial_operator(self):
             pybamm.div(2 * pybamm.grad(var)),
             pybamm.div(2 * pybamm.grad(var)) + 3 * var,
             -2 * pybamm.div(var * pybamm.grad(var) + 2 * pybamm.grad(var)),
+            pybamm.laplacian(var),
         ]:
             # Check that the equation can be evaluated in each case
             # Dirichlet

tests/unit/test_spatial_methods/test_finite_volume/test_ghost_nodes.py tests/unit/test_spatial_methods/test_finite_volume/test_ghost_nodes_and_neumann.py

@@ -49,9 +49,13 @@ def test_add_ghost_nodes(self):
         bcs = {"left": (pybamm.Scalar(0), "x"), "right": (pybamm.Scalar(3), "Neumann")}
         with self.assertRaisesRegex(ValueError, "boundary condition must be"):
             sp_meth.add_ghost_nodes(var, discretised_symbol, bcs)
+        with self.assertRaisesRegex(ValueError, "boundary condition must be"):
+            sp_meth.add_neumann_values(var, discretised_symbol, bcs, var.domain)
         bcs = {"left": (pybamm.Scalar(0), "Neumann"), "right": (pybamm.Scalar(3), "x")}
         with self.assertRaisesRegex(ValueError, "boundary condition must be"):
             sp_meth.add_ghost_nodes(var, discretised_symbol, bcs)
+        with self.assertRaisesRegex(ValueError, "boundary condition must be"):
+            sp_meth.add_neumann_values(var, discretised_symbol, bcs, var.domain)
 
     def test_add_ghost_nodes_concatenation(self):
         # Set up