Class Projectile

src/csm/ch03/Projectile.java:19–95

Projectile models the dynamics of a projectile and forms a template for other simulations. @author Wolfgang Christian, Jan Tobochnik, Harvey Gould @version 1.0 05/16/05

 * @version 1.0  05/16/05
 */
public class Projectile implements Drawable, ODE {
  static final double g = 9.8;
  double[] state = new double[5]; // {x,vx,y,vy,t}
  int pixRadius = 6;              // pixel radius for drawing of projectile
  EulerRichardson odeSolver = new EulerRichardson(this);

  public void setStepSize(double dt) {
    odeSolver.setStepSize(dt);
  }

  /**
   * Steps (advances) the time.
   *
   * @param dt the time step.
   */
  public void step() {
    odeSolver.step(); // do one time step using selected algorithm
  }

  /**
   * Sets the state.
   *
   * @param x
   * @param vx
   * @param y
   * @param vy
   */
  public void setState(double x, double vx, double y, double vy) {
    state[0] = x;
    state[1] = vx;
    state[2] = y;
    state[3] = vy;
    state[4] = 0;
  }

  /**
   * Gets the state.  Required for ODE interface.
   * @return double[] the state
   */
  @Override
public double[] getState() {
    return state;
  }

  /**
   * Gets the rate.  Required for ODE inteface
   * @param state double[] the state
   * @param rate double[]  the computed rate
   */
  @Override
public void getRate(double[] state, double[] rate) {
    rate[0] = state[1]; // rate of change of x
    rate[1] = 0;        // rate of change of vx
    rate[2] = state[3]; // rate of change of y
    rate[3] = -g;       // rate of change of vy
    rate[4] = 1;        // dt/dt = 1
  }