Solvers

Dummy Solver

# Base Solver¶

class pybamm.BaseSolver(method=None, rtol=1e-06, atol=1e-06, root_method=None, root_tol=1e-06, extrap_tol=0)[source]

Solve a discretised model.

Parameters
• method (str, optional) – The method to use for integration, specific to each solver

• rtol (float, optional) – The relative tolerance for the solver (default is 1e-6).

• atol (float, optional) – The absolute tolerance for the solver (default is 1e-6).

• root_method (str or pybamm algebraic solver class, optional) – The method to use to find initial conditions (for DAE solvers). If a solver class, must be an algebraic solver class. If “casadi”, the solver uses casadi’s Newton rootfinding algorithm to find initial conditions. Otherwise, the solver uses ‘scipy.optimize.root’ with method specified by ‘root_method’ (e.g. “lm”, “hybr”, …)

• root_tol (float, optional) – The tolerance for the initial-condition solver (default is 1e-6).

• extrap_tol (float, optional) – The tolerance to assert whether extrapolation occurs or not. Default is 0.

calculate_consistent_state(model, time=0, inputs=None)[source]

Calculate consistent state for the algebraic equations through root-finding. model.y0 is used as the initial guess for rootfinding

Parameters
• model (`pybamm.BaseModel`) – The model for which to calculate initial conditions.

• time (float) – The time at which to calculate the states

• inputs (dict, optional) – Any input parameters to pass to the model when solving

Returns

y0_consistent – Initial conditions that are consistent with the algebraic equations (roots of the algebraic equations). If self.root_method == None then returns model.y0.

Return type

array-like, same shape as y0_guess

check_extrapolation(solution, events)[source]

Check if extrapolation occurred for any of the interpolants. Note that with the current approach (evaluating all the events at the solution times) some extrapolations might not be found if they only occurred for a small period of time.

Parameters
copy()[source]

Returns a copy of the solver

get_termination_reason(solution, events)[source]

Identify the cause for termination. In particular, if the solver terminated due to an event, (try to) pinpoint which event was responsible. If an event occurs the event time and state are added to the solution object. Note that the current approach (evaluating all the events and then finding which one is smallest at the final timestep) is pretty crude, but is the easiest one that works for all the different solvers.

Parameters
set_up(model, inputs=None, t_eval=None, ics_only=False)[source]

Unpack model, perform checks, and calculate jacobian.

Parameters
• model (`pybamm.BaseModel`) – The model whose solution to calculate. Must have attributes rhs and initial_conditions

• inputs (dict, optional) – Any input parameters to pass to the model when solving

• t_eval (numeric type, optional) – The times (in seconds) at which to compute the solution

solve(model, t_eval=None, external_variables=None, inputs=None, initial_conditions=None, nproc=None, calculate_sensitivities=False)[source]

Execute the solver setup and calculate the solution of the model at specified times.

Parameters
• model (`pybamm.BaseModel`) – The model whose solution to calculate. Must have attributes rhs and initial_conditions

• t_eval (numeric type) – The times (in seconds) at which to compute the solution

• external_variables (dict) – A dictionary of external variables and their corresponding values at the current time

• inputs (dict or list, optional) – A dictionary or list of dictionaries describing any input parameters to pass to the model when solving

• initial_conditions (`pybamm.Symbol`, optional) – Initial conditions to use when solving the model. If None (default), model.concatenated_initial_conditions is used. Otherwise, must be a symbol of size len(model.rhs) + len(model.algebraic).

• nproc (int, optional) – Number of processes to use when solving for more than one set of input parameters. Defaults to value returned by “os.cpu_count()”.

• calculate_sensitivites (list of str or bool) – If true, solver calculates sensitivities of all input parameters. If only a subset of sensitivities are required, can also pass a list of input parameter names

Returns

If type of inputs is list, return a list of corresponding `pybamm.Solution` objects.

Return type

`pybamm.Solution` or list of `pybamm.Solution` objects.

Raises

pybamm.ModelError – If an empty model is passed (model.rhs = {} and model.algebraic={} and model.variables = {})

step(old_solution, model, dt, npts=2, external_variables=None, inputs=None, save=True)[source]

Step the solution of the model forward by a given time increment. The first time this method is called it executes the necessary setup by calling self.set_up(model).

Parameters
• old_solution (`pybamm.Solution` or None) – The previous solution to be added to. If None, a new solution is created.

• model (`pybamm.BaseModel`) – The model whose solution to calculate. Must have attributes rhs and initial_conditions

• dt (numeric type) – The timestep (in seconds) over which to step the solution

• npts (int, optional) – The number of points at which the solution will be returned during the step dt. default is 2 (returns the solution at t0 and t0 + dt).

• external_variables (dict) – A dictionary of external variables and their corresponding values at the current time

• inputs (dict, optional) – Any input parameters to pass to the model when solving

• save (bool) – Turn on to store the solution of all previous timesteps

Raises

pybamm.ModelError – If an empty model is passed (model.rhs = {} and model.algebraic = {} and model.variables = {})