org.opensourcephysics.numerics
Interface StateEvent

All Superinterfaces:

MultiVarFunction

public interface StateEvent
extends MultiVarFunction

StateEvent defines an event consisting in that a given numeric value changes sign from positive to negative. This numeric value usually consists in an expression of the variables of an ODE. Every valid model state must (in principle) provide a value f(t)>=+tolerance at every instant of time, where tolerance is a (small positive) number prescribed by the user. However, values in the range (-tolerance,+tolerance) are still accepted. The event really happens when the value at the next instant of time satisfies f(t+dt)<=-tolerance. Then, finding the moment when the event takes place corresponds to finding a root of f(t). More precisely, and because of numerical approximation, a root is considered to be found when -tolerance=+tolerance) or, if this is not true, at least the state at the next instant t+dt will not trigger an event (i.e. f(t+dt)>-tolerance). (If this rule is violated an infinite loop may be caused.)

Author:

Francisco Esquembre (Feb 2004, corrected May 2005)

Method Summary

boolean	action() What to do when the event has taken place.
double	evaluate(double[] state) Returns the value f(t) for a given state of the model.
double	getTolerance() Returns the tolerance for the event.

Method Detail

getTolerance

double getTolerance()

Returns the tolerance for the event.

Returns:

the tolerance

evaluate

double evaluate(double[] state)

Returns the value f(t) for a given state of the model. The values returned by this method will be used by the solver to find the exact time at which the event took place.

Specified by:

evaluate in interface MultiVarFunction

Parameters:

state - The current state of the ODE

Returns:

the value for this state

action

boolean action()

What to do when the event has taken place. The return value tells the solver wether it should stop the computation at the exact moment of the event or continue solving the ODE for the rest of the prescribed dt.

Returns:

true if the solver should return at this instant of time, false otherwise.