Move initial soc out of solve

[aabills]

Description

It would be nice if it was in its own method, which was then called by either solve or build.

Motivation

Necessary to get initial soc for Julia solvers

Possible Implementation

just move it to its own method, then call that method in build/solve

Additional context

No response

[valentinsulzer]

It's already mostly in a separate method get_initial_stoichiometries.

PyBaMM/pybamm/simulation.py

Lines 605 to 624 in 91a97cd

	c_n_init = self.parameter_values[
	"Initial concentration in negative electrode [mol.m-3]"
	]
	c_p_init = self.parameter_values[
	"Initial concentration in positive electrode [mol.m-3]"
	]
	param = pybamm.LithiumIonParameters()
	c_n_max = self.parameter_values.evaluate(param.n.prim.c_max)
	c_p_max = self.parameter_values.evaluate(param.p.prim.c_max)
	x, y = pybamm.lithium_ion.get_initial_stoichiometries(
	initial_soc, self.parameter_values
	)
	self.parameter_values.update(
	{
	"Initial concentration in negative electrode [mol.m-3]": x
	* c_n_max,
	"Initial concentration in positive electrode [mol.m-3]": y
	* c_p_max,
	}
	)

What are the inputs/outputs you need for the julia stuff?

[aabills]

I just want to access it from build. S/b trivial

[valentinsulzer]

Yes, it's easy. We need to also keep it in solve though, no good reason to break backwards compatibility here