dynode

A framework for modelling and simulation of dynamical systems in the form of ordinary differential equations.

class dynode.Recorder

Generic recorder functor.

Can be used as an observer in conjunction with a Simulation.

property results

The recorded results

Returns

The recorded results as a dict

Return type

dict

store(system: Type[dynode.system.SystemInterface], attribute: str, alias: Optional[str] = None) → None

Register a variable/parameter of a system for storing.

Parameters

• system (Type[SystemInterface]) – System that owns this variable/parameter

• attribute (str) – A string of the form x.y.z pointing to the variable/parameter to be stored

• alias (Optional[str], optional) – A string under which the stored attribute will be available at. Defaults to None.

Raises

AttributeError – If the provided attribute does not exist on system

class dynode.Simulation

A simulation.

Representing a set of connected or unconnected dynamical systems that can be stepped forward in time by a numerical integration scheme.

add_observer(observer: Callable) → None

Add an observer to the simulation.

An observer is a callable of the form:

def observer(t : int, states : np.ndarray) -> None:

An observer can return True to signal that the simulation should break early:

def observer(t : int, states : np.ndarray) -> bool:
    return True

Parameters

observer (Callable) – A callable that will be called every observer_dt.

Raises

ValueError – If observer has already been added to the simulation.

Returns

A de-registering function. By calling this, observer

will be removed from the list of observers.

Return type

Callable

add_system(system: Type[dynode.system.SystemInterface]) → None

Adds a system to the simulation.

Parameters

system (Type[SystemInterface]) – The system to add, adhering to the interface provided by SystemInterface.

Raises

ValueError – If system has already been added to the simulation.

simulate(t: float, observer_dt: float, fixed_step: bool = False, integrator: str = 'dopri5', **kwargs) → int

Perform simulation.

Step the collection of systems forward in time, t seconds while informing any observer`s about the progress every `observer_dt interval. If fixed_step=True, observer_dt is also used as the internal step size of the solver, leaving the user in charge of choosing a reasonable step size for the problem at hand.

Parameters

• t (float) – Total time to progress

• observer_dt (float) – Timestep with which the observers will be invoked.

• fixed_step (bool, optional) – If True, observer_dt is used as the internal step size of the solver. Defaults to False.

• integrator (str, optional) – Which solver to use, this argument is directly forwarded to scipy.integrate.ode. Defaults to “dopri5”.

Raises

• RuntimeError – If there are no systems added to the simulation

• RuntimeError – If there are no states/ders to be integrated

• RuntimeError – The solver fails due to numerical instabilities

Returns

The current time of the simulation.

Return type

int

property systems

Systems part of this simulation

Returns

A list of the systems added to this simulation

Return type

List[SystemInterface]

class dynode.SystemInterface

Abstract Base Class (ABC) defining the System Interface.

A child class must implement the do_step method.

add_post_connection(connection_func: Callable, dependees: Optional[List[Callable]] = None) → Callable

Add a post-connection to the system.

connection_func is a callable of the form:

def connection_func(system : SystemInterface, time : int):
    pass

Parameters

• connection_func (Callable) – The connection function to add

• dependees (Optional[List[Callable]], optional) – A list of dependees that connection_func depends on. A topological sort will be performed to ensure all post-connections are executed in the correct order. Defaults to None.

Raises

ValueError – If connection_func has already been added.

Returns

A de-registering function. By calling this, connection_func

will be removed from the list of post-connections.

Return type

Callable

add_pre_connection(connection_func: Callable, dependees: Optional[List[Callable]] = None) → Callable

Add a pre-connection to the system.

connection_func is a callable of the form:

def connection_func(system : SystemInterface, time : int):
    pass

Parameters

• connection_func (Callable) – The connection function to add

• dependees (Optional[List[Callable]], optional) – A list of dependees that connection_func depends on. A topological sort will be performed to ensure all pre-connections are executed in the correct order. Defaults to None.

Raises

ValueError – If connection_func has already been added.

Returns

A de-registering function. By calling this, connection_func

will be removed from the list of pre-connections.

Return type

Callable

add_subsystem(sub_system: Type[dynode.system.SystemInterface]) → None

Add a subsystem to this system

Parameters

sub_system (Type[SystemInterface]) – The subsystem to add

Raises

ValueError – If the subsystem is self

property connections

All connection callbacks registered to this system.

Sorted in topological order

Returns

Sorted list of connection callbacks

Return type

List[Callable]

property ders

The derivatives of this system

Readable and writeable as both attributes and keys. Must be of scalar or sequence type!

Returns

Derivatives of this system

Return type

VariableContainer

abstract do_step(time: float)

Abstract method to be implemented by child classes!

Parameters

time (float) – Current simulation time

property inputs

The inputs of this system

Readable and writeable as both attributes and keys. Can be any type.

Returns

Inputs of this system

Return type

ParameterContainer

property outputs

The outputs of this system

Readable and writeable as both attributes and keys. Can be any type.

Returns

Outputs of this system

Return type

ParameterContainer

property states

The states of this system

Readable and writeable as both attributes and keys. Must be of scalar or sequence type!

Returns

States of this system

Return type

VariableContainer

property subsystems

The subsystems of this system

Returns

A list of subsystems adhering to the

SystemInterface interface

Return type

List[Type[SystemInterface]]

dynode.connect_signals(first: Union[dynode.containers.VariableContainer, dynode.containers.ParameterContainer], first_key: str, second: Union[dynode.containers.VariableContainer, dynode.containers.ParameterContainer], second_key: str) → Callable

Explicitly connect two variables/parameters.

Returns a callable that connects first_key of first to second_key of second. The callable can be used as a pre-step and/or post-step connection. Connecting state x on sys1 to input a on sys2:

sys1.add_post_connection(
    connect_signals(sys1.states, "x", sys2.inputs, "a")
)

Parameters

• first (Union[VariableContainer, ParameterContainer]) – The container to connect from

• first_key (str) – The variable name in first to connect from

• second (Union[VariableContainer, ParameterContainer]) – The container to connect to

• second_key (str) – The variable name in second to connect to

Returns

A connection callable

Return type

Callable