DiffEqState

class braincell.quad.DiffEqState

Marker mixin for a state that participates in numerical integration.

A DiffEqState is the unit of work consumed by every solver in braincell.quad. It contributes two slots — derivative and diffusion — that the surrounding solver writes during one ODE/SDE step:

• derivative is the right-hand side \(f(t, y)\) for an ODE \(\dot y = f(t, y)\), or the drift term for an SDE \(dy = f(t, y)\,dt + g(t, y)\,dW\).

• diffusion is the SDE noise coefficient \(g(t, y)\). It stays None for plain ODE systems.

This class is a brainstate.mixin.Mixin, not a brainstate.State. It carries no storage and cannot be instantiated; DiffEqState(value) raises TypeError. Mixing it into something that is not a brainstate.State yields an object no solver will accept. Use state() to allocate, or name DiffEqSingleState / DiffEqGroupState explicitly.

Separating the marker from the storage layout is what lets the two concrete classes be siblings. Solver state selection goes through isinstance(value, DiffEqState) (see braincell.quad._util.split_diffeq_states()), which stays True for both.

Variables:

• derivative (brainstate.typing.PyTree) – Time derivative (or SDE drift) of the state. Set inside DiffEqModule.compute_derivative(). Must carry units that satisfy unit(derivative) * unit(dt) == unit(value).

• diffusion (brainstate.typing.PyTree) – Optional SDE diffusion coefficient. None denotes a deterministic ODE system.

See also

DiffEqSingleState

Concrete ungrouped state, used by SingleCompartment.

DiffEqGroupState

Concrete grouped state, used by Cell.

DiffEqModule

Container that owns and updates the states.

property derivative

Get the derivative of the state.

Returns:

The derivative of the state, used to compute the derivative of the ODE system or the drift of the SDE system.

Return type:

brainstate.typing.PyTree

property diffusion

Get the diffusion of the state.

Returns:

The diffusion of the state, used to compute the diffusion of the SDE system. If it is None, the system is considered as an ODE system.

Return type:

brainstate.typing.PyTree