PendelErzwODE

package odend;

import Jama.*;

/**
 * ODE describing a mathematical pendulum with friction,<br>
 * driven by a harmonically varying force
 */
public class PendelErzwODE extends ODE {
  
  protected double  lambda = 5.0/10.0;       // friction coefficient
  protected double  A      = 12.0/10.0;      // amplitude 
  protected double  omega  = 6667.0/10000.0;    // frequency
  
  /**
   * construct from given initial conditions phi(t0), phi'(t0)
   */
  public PendelErzwODE(double phi0, double phidot0, double t0) {
    super(new Matrix(2,1), t0);	
    x0.set(0,0, phi0);
    x0.set(1,0, phidot0);
  }

  /**
   * r.h.s. giving the forced damped pendulum
   */
  public Matrix f(Matrix x, double t) {
    Matrix result = new Matrix(2,1);
    
    result.set(0,0, x.get(1,0));   // x(0)' = x(1) = v
    result.set(1,0, -lambda * x.get(1,0) - Math.sin(x.get(0,0)) +
	       A * Math.cos(omega * t));
    return result;
  }

  /**
   * set the amplitude of the external force
   */
  public void setA(double A) {
    this.A = A;
  }

  /**
   * set the friction coefficient of the pendulum
   */
  public void setLambda(double lambda) {
    this.lambda = lambda;
  }

  /**
   * set the angular frequency of the external force
   */
  public void setOmega(double omega) {
    this.omega = omega;
  }
}