[Bug]: IDAKLUSolver output variables

[rtimms]

PyBaMM Version

24.9

Python Version

3.11

Describe the bug

Running the same experiment but with cycles tagged differently can make the IDAKLUSolver return a solution without all the variables.

@MarcBerliner @martinjrobins

Steps to Reproduce

model = pybamm.lithium_ion.SPM()
parameter_values = pybamm.ParameterValues("Chen2020")
solver = pybamm.IDAKLUSolver()

# works
experiment1 = pybamm.Experiment(
    [
        (
            "Rest for 1 hour",
            "Charge at C/5 until 4.2 V",
            "Hold at 4.2 V until C/20",
        ),
    ]
)
sim1 = pybamm.Simulation(
    model, parameter_values=parameter_values, experiment=experiment1, solver=solver
)
sim1.solve()
sim1.plot()

# fails
experiment2 = pybamm.Experiment(
    [
        ("Rest for 1 hour"),
        (
            "Charge at C/5 until 4.2 V",
            "Hold at 4.2 V until C/20",
        ),
    ]
)
sim2 = pybamm.Simulation(
    model, parameter_values=parameter_values, experiment=experiment2, solver=solver
)
sim2.solve()
sim2.plot()

Relevant log output

KeyError: "Cannot process variable 'Negative particle surface concentration [mol.m-3]' as it was not part of the solve. Please re-run the solve with output_variables set to include this variable."

[kratman]

@rtimms This one is a known issue: #4386

[rtimms]

But here I am not using output_variables, so I think this is slightly different to #4386

[kratman]

Hopefully it is fixed along with the other issue. I think @pipliggins was working on it

[MarcBerliner]

@kratman I believe this is unrelated to #4386

@rtimms this is a bug, but I think we're seeing strange behavior here because the cell is at 100% SOC, and you're charging it in the second step, which instantaneously violates the voltage limit. I can look into this if it's blocking

[rtimms]

Yeah, not a huge blocker. I also think that is what is happening, but it is handled more nicely by the other solvers. Just a random edge case I came across.