Agent

Description

agent = Agent(name, model, controller, T_s, x0, uPrev_0 = zeros(n_u, 1));

An agent handles the actual execution of the simulation of a model and controller. In this sense, it also tracks the simulation history (i.e. state trajectory, inputs and realised disturbances) as well as the current simulation state.

The agent is called by the simulation at three different points. During negotiation between agents (doNegotiation), for the execution of the actual simulation step (doStep) and for eventually storing the simulation results (storeHistory).

The agent derives the optimal input on the modelled system in getOptimalTrajectory, by either calling the controller directly or by performing pareto evaluation on the model and controller.

An agents history and current status, which contains the predictions made in current timestep, are public and accessible by other agents as well as evaluation functions and disturbance prediction functions. That way, agents can make decision based on each other's state, and disturbances and evaluations can be state-aware (across the agents).

As all main PARODIS classes, the Agent class derived off the handle class, meaning that each agent has one unique instance across the simulation, allowing for read and write access from all other agents during the simulation, allowing for complex agent interactions.

Public Properties

Property	Description
controller	A Controller object, used for deriving an optimal input trajectory and for disturbance prediction
model	A model struct, containing the respective model
history	struct containing the simulation history
config	struct containing the agent's configuration
status	struct containing the current status
previousStatus	struct containing the status of the previous timestep
name	string with the agent's name during the simulation
callbackMeasureState	optional callback that can manipulate the agent's history based on other agents, called in measureState()
callbackNegotation	optional callback that is called in doNegotiation to perform negotiation tasks
simulation	Reference to the simulation in which the agent is contained

Configuration

Property	Default value	Description
T_s	[]	Time steps for each step in the prediction horizon, length(T_s) == N_pred
solver	'gurobi'	Solver to be called by YALMIP to solve MPC problem
evalFuns	struct	Struct used for storing evaluation functions, interfaced by addEvalFunction
disturbanceMeasured	false	Whether to set the prediction d(0
debugMode	false	Will toggle YALMIP debug mode and verbosity = 2 and disable use of optimizer
testFeasibility	false	If enabled, every time before actual problem is solved, an empty problem (no objective function, but set constraints) will be solved using optimize() to test if the constraints are infeasible
verboseOptimizer	false	If true, the optimizer flags debug = 1 and verbose = 2 will be set, independently of debugMode
pauseOnError	false	If set to 'on', simulation will pause right after plotting, if solver code returned from getOptimalInput is not 0 (successfully solved). Alternatively, can be set to pause only on specific codes, e.g. pauseOnError = 12 (see solver codes)
solverOptions	{}	List of additional (solver) options that will be passed so sdpsettings when initialising the controller (e.g. {'quadprog.maxIter', 1000})
reuseNegotiationResult	If agent engages in negotiation and has derived an optimal input, if this flag is set to true, this result will be reused in the agent's doStep
doParetoOnlyOnce	false	If the ParetoController is used an this flag is set to true, pareto evaluation will only be done once in a given timestep, meaning that if agent is called multiple times during negotiation, only the first call will result in a pareto evaluation

History

In the agent's history struct, all realised simulation values are stored. This includes the actual state trajectory, the actual applied inputs and disturbances, the values of the configured evaluation functions as well as of the cost functions, and the weights associated with the cost functions.

The history is used to store and access the actual state of the system. Thus, it is updated only within doStep of the agent, when the derived input will be applied to the system together with the actual disturbance. The resulting state is stored into the history, together with the input, disturbance, the value of the evaluation function calculated on this resulting state.

An agent's history is also acccessed by the figures to plot depending plots.

Field	Description
x	Matrix $n_x \times N_{simulation+1}$ containing the realised state trajectory
u	Matrix $n_u \times N_{simulation}$ containing the inputs applied to the system
d	Matrix $n_d \times N_{simulation}$ containing the disturbances applied to the system
evalValues	struct where each field contains a $1 \times N_{simulation}$ vector containing the results of the respective eval function
costs	struct where each field contains a $1 \times N_{simulation}$ vector containing the results of the respective cost function
weights	Matrix $N_{simulation} \times N_{objectives}$ containing the weights of each cost function
simulationTime	Matrix $1 \times N_{simulation}$ containing the agent's simulation time
pareto	struct with pareto history, all fields are empty if pareto evaluation is deactivated
pareto.fronts	Cell array containing the retrieved pareto front at each timestep
pareto.weights	Cell array containing the weights corresponding to the points on the front at each timestep
pareto.utopias	Matrix $N_{simulation} \times N_{objectives}$ containing the utopia points of each front
pareto.nadir	Matrix $N_{simulation} \times N_{objectives}$ containing the nadir points of each front

Status

In the status struct, all predictions and assumed values of the current timestep are stored. The status is first set by doNegotiation, if negotiation is performed. It remains set until right after the actual simulation step is performed and the history updated. Afterwards, alle fields except k are cleared, and k is increased by one.

According to execution order in the negotiation loop (and the main loop for that matter), an agent's status can be used to determine parameter values or disturbance of other agents, and to track progress in the negotiation process.

Since all the predictions become void right after the actual simulation step is performed, the status is cleared of all predictions.

Field	Description
k	Current local simulation step
xPred	Cell array containing predicted state trajectory for each scenario
uPred	Latest derived predicted optimal input trajectory
dPred	Cell array containing predicted disturbances for each scenario
evalPred	struct, each field contains vector containing predicted eval values over horizon
costsPred	struct, each field contains vector containing predicted cost function values over horizon
paramValues	The currently determined parameter values
chosenWeights	The weights chosen for the current timestep
horizonTime	Vector with the simulation times of the current horizon
slackVariables	The determined values of the configured slack variables
pareto	struct with pareto status, all fields are empty if pareto evaluation is deactivated
pareto.front	the current evaluated pareto front
pareto.lastStepWithPareto	the last local time step at which pareto evaluation was performed

Negotiation

If an agent's behaviour is dependent on other agents, this can be mapped using the negotiation functionality. At the beginning of each simulation step, so when all agents' time steps match, the negotiation loop will be initiated. This is either done by defining a static negotiation order in which the agents' doNegotiation() methods will be called, or by calling a completely user-defined negotiation callback, which makes use of doNegotiation() in some way.

Below shows what happens in an agent's doNegotiation method, which should help understand at which point the negotiation callback comes into place and how you can work with it.

function doNegotiation(this)
    % doNegotation    Executes a negotiation step for the agent

    this.measureState();
    this.status.dPred = this.getDisturbance();
    this.setParameterValues();

    this.status.uPred = this.getOptimalTrajectory();
    if ~isempty(this.callbackNegotiation)
        this.callbackNegotiation(this, this.simulation);
    end
end

The negotiation callback will be called with the calling agent and the simulation object of the current simulation. In this simulation object there is a shared struct, which can be used to exchange information between agents during the negotiation loop.

State Measurement

[] = callbackMeasureState(agent, simulation)

State measurement in PARODIS is completely user-defined. If the callback callbackMeasureState is set, it is called in the measureState method of the agent. The callback is not expected to return any data, but instead to directly manipulate the agent's history and/or state.

This callback can be useful to update coupled systems to their actual state after a simulation step.

Pareto Evaluation

The Agent object calls the Pareto object's methods for calculating the Pareto front in three steps:

1. Call the extreme point function for calculating at least n extreme points.
2. Call the Pareto front determination scheme to calculate Pareto-optimal points on the Pareto front.
3. Call either the Interactivity Tool for selecting one Pareto-optimal point or call the selected metric function for automatically choosing a suitable Pareto-optimal point.