[Bug]: Solution last_state can't be used as a starting solution

[brosaplanella]

PyBaMM Version

23.2

Python Version

3.9.16

Describe the bug

When trying to use the last_state as a starting solution for a new simulation it breaks because

AttributeError: 'Solution' object has no attribute 'steps'

The issue seems to be here:

PyBaMM/pybamm/simulation.py

Line 663 in 81d8c35

starting_solution.steps,

Steps to Reproduce

import pybamm

model = pybamm.lithium_ion.SPM()

experiment = pybamm.Experiment(["Discharge at 1C until 3.5 V"])
sim = pybamm.Simulation(model, experiment=experiment)
solution = sim.solve()

experiment2 = pybamm.Experiment(["Discharge at 1C until 2.5 V"])
sim2 = pybamm.Simulation(model, experiment=experiment2)
solution2 = sim2.solve(starting_solution=solution.last_state)

Relevant log output

Traceback (most recent call last):
  File "/home/brosaplanella/support-pybamm/.github/profile/mwe.py", line 11, in <module>
    solution2 = sim2.solve(starting_solution=solution.last_state)
  File "/home/brosaplanella/support-pybamm/env/lib/python3.9/site-packages/pybamm/simulation.py", line 663, in solve
    starting_solution.steps,
AttributeError: 'Solution' object has no attribute 'steps'

[valentinsulzer]

This is a bug, easiest way to fix it is to add some extra logic for that case in simulation.py (i.e. initialize steps to be an empty list)

[manjunathnilugal]

Is there is any method to fix this issue as of now until the issues is resolved.
It is mentioned to to add steps = [ ], in simulation.py file, @tinosulzer could you please tell in brief.

[manjunathnilugal]

How to implement this in the current version of pybamm, i.e. in my local system

[jsbrittain]

@manjunathnilugal Hi - The change has been merged so should be available immediately in the develop branch. If you want to make this change in your local system, you will need to alter this line in simulation.py to [starting_solution] as here.