HyperbolicTangentSigmoid.java

package func.nn.activation;

/**
 * The tanh sigmoid function
 * @author Andrew Guillory gtg008g@mail.gatech.edu
 * @version 1.0
 */
public class HyperbolicTangentSigmoid 
		extends DifferentiableActivationFunction{

   /**
    * @see nn.function.DifferentiableActivationFunction#derivative(double)
    */
	public double derivative(double value) {
		double tanhvalue = value(value);
		return 1 - tanhvalue * tanhvalue;
	}

	/**
	 * @see nn.function.ActivationFunction#activation(double)
	 */
    public double value(double value) {
        double e2x = Math.exp(2 * value);
        if (e2x == Double.POSITIVE_INFINITY) {
            return 1;
        } else {
            return (e2x - 1) / (e2x + 1);
        }
	}
	

}