Merge pull request #1510 from pybamm-team/issue-1507-check_algebraic_equations

#1507 remove algebraic equation check

Author: rtimms

CHANGELOG.md

@@ -26,6 +26,7 @@
 
 ## Bug fixes
 
+-   Removed the overly-restrictive check "each variable in the algebraic eqn keys must appear in the eqn" ([#1510](https://github.com/pybamm-team/PyBaMM/pull/1510))
 -   Made parameters importable through pybamm ([#1475](https://github.com/pybamm-team/PyBaMM/pull/1475))
 
 ## Breaking changes

pybamm/models/base_model.py

@@ -639,40 +639,20 @@ def check_well_determined(self, post_discretisation):
 
     def check_algebraic_equations(self, post_discretisation):
         """
-        Check that the algebraic equations are well-posed.
-        Before discretisation, each algebraic equation key must appear in the equation
-        After discretisation, there must be at least one StateVector in each algebraic
-        equation
+        Check that the algebraic equations are well-posed. After discretisation,
+        there must be at least one StateVector in each algebraic equation.
         """
-        vars_in_bcs = set()
-        unpacker = pybamm.SymbolUnpacker(pybamm.Variable)
-        for side_eqn in self.boundary_conditions.values():
-            all_vars = unpacker.unpack_list_of_symbols(
-                [eqn for eqn, _ in side_eqn.values()]
-            )
-            vars_in_bcs.update(all_vars.keys())
-        if not post_discretisation:
-            # After the model has been defined, each algebraic equation key should
-            # appear in that algebraic equation, or in the boundary conditions
-            # this has been relaxed for concatenations for now
-            for var, eqn in self.algebraic.items():
-                if not (
-                    any(x.id == var.id for x in eqn.pre_order())
-                    or var.id in vars_in_bcs
-                    or isinstance(var, pybamm.Concatenation)
-                ):
-                    raise pybamm.ModelError(
-                        "each variable in the algebraic eqn keys must appear in the eqn"
-                    )
-        else:
-            # variables in keys don't get discretised so they will no longer match
-            # with the state vectors in the algebraic equations. Instead, we check
-            # that each algebraic equation contains some StateVector
+        if post_discretisation:
+            # Check that each algebraic equation contains some StateVector
             for eqn in self.algebraic.values():
                 if not eqn.has_symbol_of_classes(pybamm.StateVector):
                     raise pybamm.ModelError(
                         "each algebraic equation must contain at least one StateVector"
                     )
+        else:
+            # We do not perfom any checks before discretisation (most problematic
+            # cases should be caught by `check_well_determined`)
+            pass
 
     def check_ics_bcs(self):
         """Check that the initial and boundary conditions are well-posed."""

pybamm/models/submodels/current_collector/effective_resistance_current_collector.py

@@ -350,7 +350,7 @@ def __init__(self):
             f_p: pybamm.laplacian(f_p)
             - pybamm.source(1, f_p)
             + c * pybamm.DefiniteIntegralVector(f_p, vector_type="column"),
-            c: pybamm.yz_average(f_p) + pybamm.NotConstant(0) * c,
+            c: pybamm.yz_average(f_p),
         }
 
         # Boundary conditons

pybamm/models/submodels/current_collector/quite_conductive_potential_pair.py

@@ -67,9 +67,7 @@ def set_algebraic(self, variables):
             * pybamm.laplacian(phi_s_cp)
             + pybamm.source(i_boundary_cc_0, phi_s_cp)
             + c * pybamm.PrimaryBroadcast(cc_area, "current collector"),
-            c: pybamm.Integral(i_boundary_cc, z)
-            - applied_current / cc_area
-            + pybamm.Multiplication(0, c),
+            c: pybamm.Integral(i_boundary_cc, z) - applied_current / cc_area,
         }
 
     def set_initial_conditions(self, variables):

tests/unit/test_models/test_base_model.py

@@ -342,18 +342,6 @@ def test_check_well_posedness_variables(self):
         with self.assertRaisesRegex(pybamm.ModelError, "extra algebraic keys"):
             model.check_well_posedness()
 
-        # before discretisation, fail if the algebraic eqn keys don't appear in the eqns
-        model = pybamm.BaseModel()
-        model.algebraic = {c: d - 2, d: d - c}
-        with self.assertRaisesRegex(
-            pybamm.ModelError,
-            "each variable in the algebraic eqn keys must appear in the eqn",
-        ):
-            model.check_well_posedness()
-        # passes when we switch the equations around
-        model.algebraic = {c: d - c, d: d - 2}
-        model.check_well_posedness()
-
         # after discretisation, algebraic equation without a StateVector fails
         model = pybamm.BaseModel()
         model.algebraic = {