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/**           __  __
 *    _____ _/ /_/ /_    Computational Intelligence Library (CIlib)
 *   / ___/ / / / __ \   (c) CIRG @ UP
 *  / /__/ / / / /_/ /   http://cilib.net
 *  \___/_/_/_/_.___/
 */
package net.sourceforge.cilib.functions.continuous.unconstrained;

import net.sourceforge.cilib.functions.ContinuousFunction;
import net.sourceforge.cilib.type.types.container.Vector;

/**
 * f(x*)=0, x*=[0,0,...,0] in [-0.5, 0.5]^n
 * 
 * Reference:
 * 
 * 
 * Suganthan, P. N., Hansen, N., Liang, J. J., Deb, K., Chen, Y., Auger, A., and Tiwari, S. (2005).
 * Problem Definitions and Evaluation Criteria for the CEC 2005 Special Session on Real-Parameter Optimization.
 * Natural Computing, 1-50.
 * 
 */
public class Weierstrass extends ContinuousFunction {
    private double a;
    private double b;
    private int kMax;
    private double constant;

    /**
     * Default constructor.
     */
    public Weierstrass() {
        this.a = 0.5;
        this.b = 3.0;
        this.kMax = 20;

        computeConstant();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Double f(Vector input) {
        double tmp = 0;

        for (int i = 0; i < input.size(); i++) {
            for(int k = 0; k <= kMax; k++) {
                tmp += Math.pow(a, k) * Math.cos(2 * Math.PI * Math.pow(b, k) * (input.doubleValueOf(i) + 0.5));
            }
        }

        return tmp - input.size() * constant;
    }

    /**
     * Sets the kMax parameter.
     * @param kMax
     */
    public void setkMax(int kMax) {
        this.kMax = kMax;
        computeConstant();
    }

    /**
     * Sets the b parameter.
     * @param b
     */
    public void setB(double b) {
        this.b = b;
        computeConstant();
    }

    /**
     * Sets the a parameter.
     * @param a
     */
    public void setA(double a) {
        this.a = a;
        computeConstant();
    }

    /**
     * This computes the second term which is a constant so it can be stored
     * separately and only needs to be computed when the function parameters
     * change.
     */
    private void computeConstant() {
        double tmp = 0.0;

        for(int k = 0; k <= kMax; k++) {
            tmp += Math.pow(a, k) * Math.cos(2 * Math.PI * Math.pow(b, k) * 0.5);
        }

        constant = tmp;
    }
}