HyperbolicTangentContrast.java

package shared.filt.ica;

/**
 * A log hyperbolic cosine contrast function
 * (the first derivative is hyperbolic tangent)
 * @author Andrew Guillory gtg008g@mail.gatech.edu
 * @version 1.0
 */
public class HyperbolicTangentContrast implements ContrastFunction {

    /**
     * @see shared.filt.ica.ContrastFunction#g(double)
     */
    public double g(double value) {
        double e2x = Math.exp(2 * value);
        if (e2x == Double.POSITIVE_INFINITY) {
            return 1;
        } else {
            return (e2x - 1) / (e2x + 1);
        }
    }

    /**
     * @see shared.filt.ica.ContrastFunction#gprime(double)
     */
    public double gprime(double value) {
        double tanhvalue = g(value);
        return 1 - tanhvalue * tanhvalue;
    }

}