#590 add some info to contributing

Author: valentinsulzer

CONTRIBUTING.md

@@ -237,6 +237,7 @@ Figuring out where to start the debugger is the real challenge. Some good ways t
 ```python3
 pybamm.set_logging_level("DEBUG")
 ```
+6. In models that inherit from `pybamm.BaseBatteryModel` (i.e. any battery model), you can use `self.process_parameters_and_discretise` to process a symbol and see what it will look like.
 
 ### Profiling
 

pybamm/models/full_battery_models/base_battery_model.py

@@ -19,6 +19,7 @@ def __init__(self, options=None, name="Unnamed battery model"):
         self._extra_options = options
         self.set_standard_output_variables()
         self.submodels = OrderedDict()  # ordered dict not default in 3.5
+        self._built = False
 
     @property
     def default_parameter_values(self):
@@ -332,7 +333,9 @@ def build_model(self):
             self.update(submodel)
 
         pybamm.logger.debug("Setting voltage variables")
-        # self.set_voltage_variables()
+        self.set_voltage_variables()
+
+        self._built = True
 
     def set_thermal_submodel(self):
 
@@ -466,6 +469,9 @@ def process_parameters_and_discretise(self, symbol):
         :class:`pybamm.Symbol`
             Processed symbol
         """
+        if not self._built:
+            self.build_model()
+
         # Set up parameters
         geometry = self.default_geometry
         parameter_values = self.default_parameter_values
@@ -474,7 +480,6 @@ def process_parameters_and_discretise(self, symbol):
         # Set up discretisation
         mesh = pybamm.Mesh(geometry, self.default_submesh_types, self.default_var_pts)
         disc = pybamm.Discretisation(mesh, self.default_spatial_methods)
-        self.build_model()
         variables = list(self.rhs.keys()) + list(self.algebraic.keys())
         disc.set_variable_slices(variables)
 

tests/unit/test_models/test_full_battery_models/test_base_battery_model.py

@@ -7,8 +7,10 @@
 
 class TestBaseBatteryModel(unittest.TestCase):
     def test_process_parameters_and_discretise(self):
-        model = pybamm.SimpleODEModel()
-        c = pybamm.Parameter("Negative electrode width [m]") * pybamm.Variable("c")
+        model = pybamm.ReactionDiffusionModel()
+        c = pybamm.Parameter("Negative electrode width [m]") * pybamm.Variable(
+            "Negative electrolyte concentration", domain="negative electrode"
+        )
         processed_c = model.process_parameters_and_discretise(c)
         self.assertIsInstance(processed_c, pybamm.Multiplication)
         self.assertIsInstance(processed_c.left, pybamm.Scalar)