ucb.proj2

Class Physics

java.lang.Object

ucb.proj2.Physics

public class Physics
extends Object

Methods for computing collision times and effects on round equal-sized moving objects in 2D. Don't change this class.

For the purposes of this package, we represent the state of an object as a four-element double[] containing [x, y, vx, vy]: the coordinates of the object's center, and the x- and y-components of its velocity.

The vector-manipulating routines add, len2, len, and ip operate on 2-element segments of arrays of doubles. To specify such a segment, you supply an array and the index of the first element of the segment. Thus, if A, V, and C are 4-element arrays, then add (C, 0, A, 0, t, V, 2) adds (A[0], A[1]) + t * (V[2], V[3]) and places the result in C[0], C[1]. In comments, we use the notation X[i:i+1] to refer to one of these two-element segments.

The computations are not exactly physical (especially when the objects interpenetrate slightly due to round-off), but they should do for this project.

Constructor Summary

Constructors

Constructor and Description
Physics()

Method Summary

Methods

Modifier and Type	Method and Description
static double[]	add(double[] Z, int iz, double[] X, int ix, double[] Y, int iy) Same as add (Z, IZ, 1.0, X, IX, 1.0, Y, IY).
static double[]	add(double[] Z, int iz, double[] X, int ix, double ay, double[] Y, int iy) Same as add (Z, IZ, 1.0, X, IX, AY, Y, IY).
static double[]	add(double[] X, int ix, double ay, double[] Y, int iy) Same as add (NZ, 0, 1.0, X, IX, AY, Y, IY), where NZ is a new double[2].
static double[]	add(double[] Z, int iz, double ax, double[] X, int ix, double ay, double[] Y, int iy) Set Z[IZ : IZ+1] to AX*X[IX : IX+1] + AY*Y[IY : IY+1], returning Z.
static double[]	add(double ax, double[] X, int ix, double ay, double[] Y, int iy) Same as add (NZ, 0, AX, X, IX, AY, Y, IY), where NZ is a new double[2].
static double	collide(double[] p0, double[] p1, double r) Given two objects with radius R with states P0 and P1 (see the class documentation for ucb.proj2.Physics, above), compute the time at which they next collide, assuming that initially, they are separated by a distance of >= 2R.
static double	ip(double[] X, int ix, double[] Y, int iy) The inner product X[IX] * Y[IY] + X[IX+1] * Y[IY+1].
static double	len(double[] X, int ix) The length of X[IX : IX+1]
static double	len(double[] X, int ix, double[] Y, int iy) The length of X[IX : IX+1] - Y[IY : IY+1].
static double	len2(double[] X, int ix) The squared length of X[IX : IX+1].
static double	len2(double[] X, int ix, double[] Y, int iy) The squared length of X[IX : IX+1] - Y[IY : IY+1].
static void	rebound(double[] p0, double[] p1) Given two objects with P0 and P1 (see the class documentation for ucb.proj2.Physics, above) that are in collision with each other, (destructively) modify their velocities as a result of that collision.

Methods inherited from class java.lang.Object

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

Constructor Detail

Physics

public Physics()

Method Detail

collide

public static double collide(double[] p0,
             double[] p1,
             double r)

Given two objects with radius R with states P0 and P1 (see the class documentation for ucb.proj2.Physics, above), compute the time at which they next collide, assuming that initially, they are separated by a distance of >= 2R. Objects that will not collide return a result of positive infinity (Double.POSITIVE_INFINITY). Objects whose centers are moving away from each others are taken not to collide.

rebound

public static void rebound(double[] p0,
           double[] p1)

Given two objects with P0 and P1 (see the class documentation for ucb.proj2.Physics, above) that are in collision with each other, (destructively) modify their velocities as a result of that collision. The objects are assumed to be spherical and of equal radius, the collision is assumed to be elastic (kinetic- energy preserving), and the material is assumed to be extremely stiff and slippery.

add

public static double[] add(double[] Z,
           int iz,
           double ax,
           double[] X,
           int ix,
           double ay,
           double[] Y,
           int iy)

Set Z[IZ : IZ+1] to AX*X[IX : IX+1] + AY*Y[IY : IY+1], returning Z.

add

public static double[] add(double[] Z,
           int iz,
           double[] X,
           int ix,
           double[] Y,
           int iy)

Same as add (Z, IZ, 1.0, X, IX, 1.0, Y, IY).

add

public static double[] add(double[] Z,
           int iz,
           double[] X,
           int ix,
           double ay,
           double[] Y,
           int iy)

Same as add (Z, IZ, 1.0, X, IX, AY, Y, IY).

add

public static double[] add(double ax,
           double[] X,
           int ix,
           double ay,
           double[] Y,
           int iy)

Same as add (NZ, 0, AX, X, IX, AY, Y, IY), where NZ is a new double[2].

add

public static double[] add(double[] X,
           int ix,
           double ay,
           double[] Y,
           int iy)

Same as add (NZ, 0, 1.0, X, IX, AY, Y, IY), where NZ is a new double[2].

ip

public static double ip(double[] X,
        int ix,
        double[] Y,
        int iy)

The inner product X[IX] * Y[IY] + X[IX+1] * Y[IY+1].

len2

public static double len2(double[] X,
          int ix)

The squared length of X[IX : IX+1].

len

public static double len(double[] X,
         int ix)

The length of X[IX : IX+1]

len2

public static double len2(double[] X,
          int ix,
          double[] Y,
          int iy)

The squared length of X[IX : IX+1] - Y[IY : IY+1].

len

public static double len(double[] X,
         int ix,
         double[] Y,
         int iy)

The length of X[IX : IX+1] - Y[IY : IY+1].