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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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 */
package jhplot.math.num.special;

/**
 * Utility class that provides methods related to the trigonometric functions.
 * 
 * @since 1.1
 * @version $Revision: 1.2 $ $Date: 2007/10/25 04:44:14 $
 */
public final class Trigonometric {

    /**
     * Default constructor.
     */
    private Trigonometric() {
        super();
    }

    /**
     * Returns the  inverse
     * hyperbolic cosine of x.
     * 
     * @param x double value for which to find the inverse hyperbolic cosine
     * @return cosh-1(x)
     * @since 1.2
     */
    public static double acosh(double x) {
        double ret;

        if (x < 1.0 || Double.isNaN(x)) {
            ret = Double.NaN;
        } else {
            ret = Math.log(x + Math.sqrt(x * x - 1.0));
        }

        return ret;
    }

    /**
     * Returns the  inverse
     * hyperbolic sine of x.
     * 
     * @param x double value for which to find the inverse hyperbolic sine
     * @return sinh-1(x)
     * @since 1.2
     */
    public static double asinh(double x) {
        double ret;

        if (Double.isNaN(x)) {
            ret = Double.NaN;
        } else {
            ret = Math.log(x + Math.sqrt(x * x + 1.0));
        }

        return ret;
    }

    /**
     * Returns the 
     * inverse hyperbolic tangent of x.
     * 
     * @param x double value for which to find the inverse hyperbolic tangent
     * @return tanh-1(x)
     * @since 1.2
     */
    public static double atanh(double x) {
        double ret;

        if (x < -1.0 || x > 1.0 || Double.isNaN(x)) {
            ret = Double.NaN;
        } else if (x == 1.0) {
            ret = Double.POSITIVE_INFINITY;
        } else if (x == -1.0) {
            ret = Double.NEGATIVE_INFINITY;
        } else {
            ret = 0.5 * (Math.log(1.0 + x) - Math.log(1.0 - x));
        }

        return ret;
    }

    /**
     * Returns the 
     * hyperbolic cosine of x.
     * 
     * @param x double value for which to find the hyperbolic cosine
     * @return cosh(x)
     */
    public static double cosh(double x) {
        double e = Math.exp(x);
        return (e + 1.0 / e) / 2.0;
    }

    /**
     * Returns the 
     * hyperbolic sine of x.
     * 
     * @param x double value for which to find the hyperbolic sine
     * @return sinh(x)
     */
    public static double sinh(double x) {
        double e = Math.exp(x);
        return (e - 1.0 / e) / 2.0;
    }

    /**
     * Returns the  hyperbolic
     * tangent of x.
     * 
     * @param x double value for which to find the hyperbolic sine
     * @return sinh(x)
     */
    public static double tanh(double x) {
        double e = Math.exp(x * 2.0);
        return (e - 1.0) / (e + 1.0);
    }
}