CasadiSolver

PyBaMM’s CasadiSolver uses the CasADi symbolic framework and SUNDIALS integrators to solve ODE and DAE battery models. It supports event detection through a configurable “mode” parameter.

pybamm.CasadiSolver wraps the CasADi integrator (backed by SUNDIALS CVODES/IDA) and adds battery-specific logic for event detection and step-and-check integration.

Constructor

pybamm.CasadiSolver(
    mode="safe",
    rtol=1e-6,
    atol=1e-6,
    root_method="casadi",
    root_tol=1e-6,
    max_step_decrease_count=5,
    dt_max=None,
    extrap_tol=None,
    on_extrapolation=None,
    extra_options_setup=None,
    extra_options_call=None,
    return_solution_if_failed_early=False,
    perturb_algebraic_initial_conditions=None,
    integrators_maxcount=100,
)

mode · str · default: "\"safe\""

Integration strategy. See Modes below.

rtol · float · default: "1e-6"

Relative tolerance for the integrator.

atol · float · default: "1e-6"

Absolute tolerance for the integrator.

root_method · str · default: "\"casadi\""

Method for computing consistent initial conditions for DAE systems. "casadi" uses CasADi’s Newton rootfinder. Any valid scipy.optimize.root method string (e.g. "lm", "hybr") is also accepted.

root_tol · float · default: "1e-6"

Tolerance for the root-finding step.

max_step_decrease_count · int · default: "5"

Maximum number of times the step size may be halved before raising an error.

dt_max · float | None · default: "600"

Maximum global step size (seconds) in "safe" mode. Defaults to 600 s when None.

extrap_tol · float | None · default: "0"

Tolerance for detecting extrapolation beyond the solved interval.

on_extrapolation · str · default: "\"error\""

Behaviour when extrapolation is detected: "error", "warn", or "ignore".

extra_options_setup · dict | None · default: "{}"

Options forwarded to the CasADi integrator at creation time. Useful keys include "max_num_steps" and "print_stats". See the CasADi docs for the full list.

extra_options_call · dict | None · default: "{}"

Options forwarded to the CasADi integrator at call time.

return_solution_if_failed_early · bool · default: "false"

If True, return a partial Solution when the solver fails mid-simulation instead of raising an error.

perturb_algebraic_initial_conditions · bool | None · default: "None"

Whether to perturb algebraic initial conditions to avoid singularities. Defaults to True in "safe" mode, False otherwise.

integrators_maxcount · int · default: "100"

LRU cache size for compiled CasADi integrators. Set to 0 for unbounded caching.

---

Modes

Mode	Description	Recommended for
"safe"	Step-and-check in global steps of dt_max, detecting events	Full charge/discharge cycles
"fast"	Direct integration; events are not tracked	Drive cycles, no cut-off events
"fast with events"	Direct integration then retroactively locates events (experimental)	Testing
"safe without grid"	Step-by-step without pre-building the time grid (experimental)	Memory-constrained runs

---

Examples

Discharge with events

import pybamm

model = pybamm.lithium_ion.DFN()
param = pybamm.ParameterValues("Chen2020")

solver = pybamm.CasadiSolver(mode="safe", rtol=1e-6, atol=1e-6)

sim = pybamm.Simulation(model, parameter_values=param, solver=solver)
sol = sim.solve([0, 3600])
print(sol["Terminal voltage [V]"].entries[-1])

"fast with events" and "safe without grid" modes are experimental and may change without notice.