Make y, z optional arguments forFunctionParameters that depend on space

[rtimms]

Some FunctionParameters depend on space and time (e.g. ambient temperature) but it doesn't always make sense to allow these to depend on space, for example if the thermal model is lumped then the temperature cannot depend on space. For the user, this can be confusing (see #3630).

Is there a nice way to be able to define these functions differently depending on the model options? Then for lumped models users can pass T(t) and if they try to pass T(y,z,t) we can catch it and throw an informative error.

[rtimms]

From @ejfdickinson

I'd feel it's most Pythonic to put optional arguments last, and explicitly allow them to be optional. In general we don't want to have to write functions whose return values don't depend on their arguments, right?

What's happened here is that you've enabled complicated behaviour by requiring simple behaviour to have a complicated calling pattern!

Yes, this should work. Let's do that

[rtimms]

In the actual model definitions, we will need to update the calls from (y,z,t) to (t, y=y, z=z) (best to be explicit in the latter in anticipation of other coordinate systems).

[cringeyburger]

Hi! I would like to take this on.

[cringeyburger]

From what I understand, we need to change the calls from (y, z, t) to (t, y=y_1, z=z_1), where y_1 and z_1 are two default values, and we need to change this call in the actual model definition, not JUST in thermal_parameters.py? (talking about T_amb method)
But what are the default values y_1 and z_1 when the model is in thermal equilibrium or lumped? The model doesn't depend on distance parameters, right? (I don't know much about batteries, so that I may be misunderstanding something)

[Rishab87]

I would like to work on this issue, can this be assigned to me?