/*
  hakank: This is my take of the Sigmoid function.

  For more about Sigmoid function, see
  http://en.wikipedia.org/wiki/Sigmoid_function
    P(t) = 1/ (1+exp(-t))

  I just copied the org.jgap.gp.function.Log and changed
  accordingly...

*/


import org.jgap.*;
import org.jgap.gp.*;
import org.jgap.gp.impl.*;
import org.jgap.util.*;

/**
 * Returns the Sigmoid of a double value.
 *
 * @author Hakan Kjellerstrand
 */
public class Sigmoid
    extends MathCommand implements ICloneable {
    
    public Sigmoid(final GPConfiguration a_conf, Class a_returnType)
        throws InvalidConfigurationException {
        super(a_conf, 1, a_returnType);
    }
    
    public String toString() {
        return "sigmoid &1";
    }
    
    /**
     * @return textual name of this command
     *
     * @author Hakan Kjellerstrand (based on Klaus Meffert's Log file)
     */
    public String getName() {
        return "Sigmoid";
    }
    
    public float execute_float(ProgramChromosome c, int n, Object[] args) {
        float f = c.execute_float(n, 0, args);
        return (float) 1.0f/(1.0f + (float)Math.exp(-f));
    }
    
    public double execute_double(ProgramChromosome c, int n, Object[] args) {
        double d = c.execute_double(n, 0, args);
        return 1.0d/(1.0d + Math.exp(-d));
    }
    
    public Object execute_object(ProgramChromosome c, int n, Object[] args) {
    return ( (Compatible) c.execute_object(n, 0, args)).execute_sigmoid();
    }
    
  protected interface Compatible {
      public Object execute_sigmoid();
  }
    /**
     * Clones the object. Simple and straight forward implementation here.
     *
     * @return cloned instance of this object
     *
     * @author Hakan Kjellerstrand (based on Klaus Meffert's Log file)
     */
    public Object clone() {
        try {
            Sigmoid result = new Sigmoid(getGPConfiguration(), getReturnType());
            return result;
        } catch (Exception ex) {
            throw new CloneException(ex);
        }
    }
}