#1477 fix bug in base_solver

Author: martinjrobins

pybamm/solvers/base_solver.py

@@ -608,9 +608,9 @@ def jacp(*args, **kwargs):
 
             # if we have changed the equations to include the explicit sensitivity
             # equations, then we also need to update the mass matrix
-            n_inputs = model.len_rhs_sens // model.len_rhs
             n_state_without_sens = model.len_rhs_and_alg
             if calculate_sensitivities_explicit:
+                n_inputs = model.len_rhs_sens // model.len_rhs
                 if model.mass_matrix.shape[0] == n_state_without_sens:
                     model.mass_matrix_inv = pybamm.Matrix(
                         block_diag(
@@ -625,8 +625,7 @@ def jacp(*args, **kwargs):
                     )
             else:
                 # take care if calculate_sensitivites used then not used
-                n_state_with_sens = model.len_rhs_and_alg * (n_inputs + 1)
-                if model.mass_matrix.shape[0] == n_state_with_sens:
+                if model.mass_matrix.shape[0] > n_state_without_sens:
                     model.mass_matrix_inv = pybamm.Matrix(
                         model.mass_matrix_inv.entries[:n_state_without_sens,
                                                       :n_state_without_sens]