State vector entries for composite electrode

PyBaMM Q&A Models
1

What do the last two entries in the state vector represent for an SPM/SPMe with a composite anode?

var_pts = {
    "x_n": 20,
    "x_s": 20, 
    "x_p": 20,
    "r_n": 20,
    "r_n_prim": 20,
    "r_n_sec": 20,
    "r_p": 20
}

When using an SPM with the var_pts above and single-phase electrode, the length of y is 42 (throughput capacity, discharge capacity, 20 x 2 for particle concentrations).

When adding "particle phases": ('2', "1"), the length is now 64. There are 20 more entries for the 20 secondary concentrations, but there are also two new entries right at the end, which weren’t present before.

2

When you run the code below, the extra two entries at the end have entries which are zero (which indicate that those are not related to initial concentration or stoichiometries). So, I guess, the two entries are the ghost entries at the edges for internal PyBaMM calculations. @Marc, any thoughts on this?

sim = pybamm.Simulation(var_pts=var_pts)

sim.build()

# — Access symbolic entries —

entries = sim.built_model.concatenated_initial_conditions.entries

# — Print symbolic variables —

print(“Index | PyBaMM Symbolic Variable”)

print(“-”*60)

for i, var in enumerate(entries):

print(f"{i:2d} | {var}")