/*
  Copyright 2012 by Sean Luke
  Licensed under the Academic Free License version 3.0
  See the file "LICENSE" for more information
*/


package ec.app.regression.func;
import ec.*;
import ec.app.regression.*;
import ec.gp.*;
import ec.util.*;

/* 
 * NegExp.java
 * 
 * Created: Mon Apr 23 17:15:35 EDT 2012
 * By: Sean Luke

 
This function appears in the Vladislavleva-B and Vladislavleva-C function sets, and is e^(-x)
 
E. Vladislavleva, G. Smits, and D. Den Hertog. Order of Nonlinearity as a Complexity Measure for Models Generated by Symbolic Regression via Pareto Genetic Programming. IEEE Trans EC, 13(2):333-349, 2009. */

/**
 * @author Sean Luke
 * @version 1.0 
 */

public class NegExp extends GPNode
    {
    public String toString() { return "negexp"; }

    public int expectedChildren() { return 1; }

    public void eval(final EvolutionState state,
        final int thread,
        final GPData input,
        final ADFStack stack,
        final GPIndividual individual,
        final Problem problem)
        {
        RegressionData rd = ((RegressionData)(input));

        children[0].eval(state,thread,input,stack,individual,problem);
        rd.x = Math.exp(0 - rd.x);
        }
    }