umontreal.iro.lecuyer.examples.PreyPred Maven / Gradle / Ivy

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SSJ is a Java library for stochastic simulation, developed under the direction of Pierre L'Ecuyer, in the Département d'Informatique et de Recherche Opérationnelle (DIRO), at the Université de Montréal. It provides facilities for generating uniform and nonuniform random variates, computing different measures related to probability distributions, performing goodness-of-fit tests, applying quasi-Monte Carlo methods, collecting (elementary) statistics, and programming discrete-event simulations with both events and processes.

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import umontreal.iro.lecuyer.simevents.*;

public class PreyPred {
   double r  = 0.005,      c  = 0.00001,
          s  = 0.01,       d  = 0.000005,     h = 5.0;
   double x0 = 2000.0,     z0 = 150.0;
   double horizon = 501.0;
   Simulator sim = new Simulator();
   Continuous x;
   Continuous z;

   public static void main (String[] args) { new PreyPred(); }

   public PreyPred() {
      x = new Preys(sim);
      z = new Preds(sim);
      sim.init();
      new EndOfSim(sim).schedule (horizon);
      new PrintPoint(sim).schedule (h);
      (sim.continuousState()).selectRungeKutta4 (h);
      x.startInteg (x0);
      z.startInteg (z0);
      sim.start();
   }

   public class Preys extends Continuous {
      public Preys(Simulator sim) { super(sim); }

      public double derivative (double t) {
         return (r * value() - c * value() * z.value());
      }
   }

   public class Preds extends Continuous {
      public Preds(Simulator sim) { super(sim); }

      public double derivative (double t) {
         return (-s * value() + d * x.value() * value());
      }
   }

   class PrintPoint extends Event {
      public PrintPoint(Simulator sim) { super(sim); }
      public void actions() {
         System.out.println (sim.time() + "  " + x.value() + "  " + z.value());
         this.schedule (h);
      }
   }

   class EndOfSim extends Event {
      public EndOfSim(Simulator sim) { super(sim); }
      public void actions() { sim.stop(); }
   }
}