org.gicentre.utils.network.traer.physics
Class Attraction

java.lang.Object
  org.gicentre.utils.network.traer.physics.AbstractForce
      org.gicentre.utils.network.traer.physics.TargetedForce
          org.gicentre.utils.network.traer.physics.TwoBodyForce
              org.gicentre.utils.network.traer.physics.Attraction

All Implemented Interfaces:

Force

public class Attraction
extends TwoBodyForce

This class implements TwoBodyForce to represent an inverse-square law force with a force constant and minimal distance. The minimal distance is necessary to avoid numerical instability associated with division by very small values. Providing a positive k creates an attractive force, a negative k creates a repulsive force

A typical use of attraction would be to implement planetary gravitation. The gravitational force G*m_1*m_2 / r^2 could be implemented as simply as supplying G (scaled appropriately to mass and distance units used elsewhere in the system), and an appropriate minimal separation to the scale of the problem.

Author:

Jeffrey Traer Bernstein, Carl Pearson and minor modifications by Jo Wood.

Nested Class Summary

Nested classes/interfaces inherited from class org.gicentre.utils.network.traer.physics.TwoBodyForce

TwoBodyForce.ForcePair

Constructor Summary

Attraction(Particle oneEnd, Particle theOtherEnd, float k, float distanceMin)
Creates an Attraction between oneEnd and theOtherEnd, with scale k and minimum distance distanceMin.

Method Summary

protected TwoBodyForce.ForcePair	forcePair() Implements the Attraction force calculation.
float	getMinimumDistance() Reports the minimum separation distance above which the attraction is applied.
float	getStrength() Reports the strength of this Attraction.
Attraction	setMinimumDistance(float d) Sets the minimum separation distance above which the attraction is applied.
Attraction	setStrength(float k) Sets the strength of this Attraction.

Methods inherited from class org.gicentre.utils.network.traer.physics.TwoBodyForce

apply, equalAndOpposite, getOneEnd, getTheOtherEnd, setOneEnd, setTheOtherEnd, specifyBoth, turnOff, turnOn, turnOn

Methods inherited from class org.gicentre.utils.network.traer.physics.TargetedForce

apply

Methods inherited from class org.gicentre.utils.network.traer.physics.AbstractForce

isOff, isOn

Methods inherited from class java.lang.Object

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

Constructor Detail

Attraction

public Attraction(Particle oneEnd,
                  Particle theOtherEnd,
                  float k,
                  float distanceMin)
           throws java.lang.NullPointerException,
                  java.lang.IllegalArgumentException

Creates an Attraction between oneEnd and theOtherEnd, with scale k and minimum distance distanceMin.

Parameters:

oneEnd - The particle at one end.

theOtherEnd - The particle at the other end.

k - the force scale between the two particles.

distanceMin - the minimum distance between particles above which the force acts.

Throws:

java.lang.NullPointerException - if either particle is null.

java.lang.IllegalArgumentException - if distanceMin is <=0.

Method Detail

getMinimumDistance

public final float getMinimumDistance()

Reports the minimum separation distance above which the attraction is applied.

Returns:

the minimum separation distance

setMinimumDistance

public final Attraction setMinimumDistance(float d)
                                    throws java.lang.IllegalArgumentException

Sets the minimum separation distance above which the attraction is applied.

Parameters:

d - the new minimum distance

Returns:

this Attraction with the new minimum distance setting.

Throws:

java.lang.IllegalArgumentException - if d<=0

setStrength

public final Attraction setStrength(float k)

Sets the strength of this Attraction. Positive k is an attractive force, negative k a repulsive one.

Parameters:

k - the strength of the Attraction.

Returns:

this Attraction with the new attractive force.

getStrength

public final float getStrength()

Reports the strength of this Attraction.

Returns:

the strength of this Attraction; positive for attractive forces, negative for repulsive forces.

forcePair

protected TwoBodyForce.ForcePair forcePair()

Implements the Attraction force calculation.

Specified by:

forcePair in class TwoBodyForce

Returns:

the ForcePair to act on oneEnd and theOtherEnd