umontreal.iro.lecuyer.simevents
Class Continuous

java.lang.Object
  umontreal.iro.lecuyer.simevents.Continuous

public abstract class Continuous
extends Object

Represents a variable in a continuous-time simulation. This abstract class provides the basic structures and tools for continuous-time simulation, where certain variables evolve continuously in time, according to differential equations. Such continuous variables can be mixed with events and processes.

Each type of continuous-time variable should be defined as a subclass of Continuous. The instances of these subclasses are the actual continuous-time variables. Each subclass must implement the method derivative which returns its derivative with respect to time. The trajectory of this variable is determined by integrating this derivative. The subclass may also reimplement the method afterEachStep, which is executed immediately after each integration step. By default (in the class Continuous), this method does nothing. This method could, for example, verify if the variable has reached a given threshold, or update a graphical illustration of the variable trajectory.

When creating a class representing a continuous variable, the toString method can be overridden to display information about the continuous variable. This information will be displayed when formating the event list as a string.

Each continuous variable has a linked simulator represented by an instance of the Simulator class. If no simulator is provided explicitly when constructing a variable, the default simulator returned by Simulator.getDefaultSimulator is used.

Constructor Summary

Continuous()
Constructs a new continuous-time variable linked to the default simulator, without initializing it.

Continuous(Simulator sim)
Constructs a new continuous-time variable linked to the given simulator, without initializing it.

Method Summary

void	afterEachStep() This method is executed after each integration step for this Continuous variable.
abstract double	derivative(double t) This method should return the derivative of this variable with respect to time, at time t.
void	init(double val) Initializes or reinitializes the continuous-time variable to val.
static void	selectEuler(double h) Selects the Euler method as the integration method, with the integration step size h, in time units, for the default simulator.
static void	selectRungeKutta2(double h) Selects a Runge-Kutta method of order 2 as the integration method to be used, with step size h.
static void	selectRungeKutta4(double h) Selects a Runge-Kutta method of order 4 as the integration method to be used, with step size h.
void	setSimulator(Simulator sim) Sets the simulator linked to this continuous-time variable.
Simulator	simulator() Returns the simulator linked to this continuous-time variable.
void	startInteg() Starts the integration process that will change the state of this variable at each integration step.
void	startInteg(double val) Same as startInteg, after initializing the variable to val.
void	stopInteg() Stops the integration process for this continuous variable.
double	value() Returns the current value of this continuous-time variable.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Continuous

public Continuous()

Constructs a new continuous-time variable linked to the default simulator, without initializing it.

Continuous

public Continuous(Simulator sim)

Constructs a new continuous-time variable linked to the given simulator, without initializing it.

Parameters:

sim - the simulator associated to this variable.

Method Detail

init

public void init(double val)

Initializes or reinitializes the continuous-time variable to val.

Parameters:

val - initial value of the variable

value

public double value()

Returns the current value of this continuous-time variable.

Returns:

the current value of the variable

simulator

public Simulator simulator()

Returns the simulator linked to this continuous-time variable.

Returns:

the current simulator of the variable

setSimulator

public void setSimulator(Simulator sim)

Sets the simulator linked to this continuous-time variable. This method should not be called while this variable is active.

Parameters:

sim - the simulator of the current variable

startInteg

public void startInteg()

Starts the integration process that will change the state of this variable at each integration step.

startInteg

public void startInteg(double val)

Same as startInteg, after initializing the variable to val.

Parameters:

val - initial value to start integration from

stopInteg

public void stopInteg()

Stops the integration process for this continuous variable. The variable keeps the value it took at the last integration step before calling stopInteg.

derivative

public abstract double derivative(double t)

This method should return the derivative of this variable with respect to time, at time t. Every subclass of Continuous that is to be instantiated must implement it. If the derivative does not depend explicitly on time, t becomes a dummy parameter. Internally, the method is used with t not necessarily equal to the current simulation time.

Parameters:

t - time at which the derivative must be computed

afterEachStep

public void afterEachStep()

This method is executed after each integration step for this Continuous variable. Here, it does nothing, but every subclass of Continuous may reimplement it.

selectEuler

public static void selectEuler(double h)

Selects the Euler method as the integration method, with the integration step size h, in time units, for the default simulator. The non-static method selectEuler in ContinuousState can be used to set the integration method for any given simulator. This method appears here only to keep compatibility with older versions of SSJ; using a non-static Simulator instance rather than the default simulator is recommended.

Parameters:

h - integration step, in simulation time units

selectRungeKutta4

public static void selectRungeKutta4(double h)

Selects a Runge-Kutta method of order 4 as the integration method to be used, with step size h. The non-static method selectRungeKutta4 in ContinuousState can be used to set the integration method for any given simulator. This method appears here only to keep compatibility with older versions of SSJ; using a non-static Simulator instance rather than the default simulator is recommended.

selectRungeKutta2

public static void selectRungeKutta2(double h)

Selects a Runge-Kutta method of order 2 as the integration method to be used, with step size h. The non-static method selectRungeKutta2 in ContinuousState can be used to set the integration method for any given simulator. This method appears here only to keep compatibility with older versions of SSJ; using a non-static Simulator instance rather than the default simulator is recommended.