Returns the inverse (arc) hyperbolic sine of a double. - Java java.lang

Java examples for java.lang:Math Trigonometric Function

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Description

Returns the inverse (arc) hyperbolic sine of a double.

Demo Code

/*//  w  ww  .  j  a  v  a  2  s . c  o m
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//package com.java2s;

public class Main {
    private static final double ASINH_COEF[] = {
            -.12820039911738186343372127359268e+0,
            -.58811761189951767565211757138362e-1,
            .47274654322124815640725249756029e-2,
            -.49383631626536172101360174790273e-3,
            .58506207058557412287494835259321e-4,
            -.74669983289313681354755069217188e-5,
            .10011693583558199265966192015812e-5,
            -.13903543858708333608616472258886e-6,
            .19823169483172793547317360237148e-7,
            -.28847468417848843612747272800317e-8,
            .42672965467159937953457514995907e-9,
            -.63976084654366357868752632309681e-10,
            .96991686089064704147878293131179e-11,
            -.14844276972043770830246658365696e-11,
            .22903737939027447988040184378983e-12,
            -.35588395132732645159978942651310e-13,
            .55639694080056789953374539088554e-14,
            -.87462509599624678045666593520162e-15,
            .13815248844526692155868802298129e-15,
            -.21916688282900363984955142264149e-16,
            .34904658524827565638313923706880e-17 };

    /**
     * Returns the inverse (arc) hyperbolic sine of a double.
     * 
     * @param x
     *            A double value.
     * @return The arc hyperbolic sine of x. If x is NaN, the result is NaN.
     */
    static public double asinh(double x) {
        double ans;
        double y = Math.abs(x);

        if (Double.isNaN(x)) {
            ans = Double.NaN;
        } else if (y <= 1.05367e-08) {
            // 1.05367e-08 = Math.sqrt(EPSILON_SMALL)
            ans = x;
        } else if (y <= 1.0) {
            ans = x * (1.0 + csevl(2.0 * x * x - 1.0, ASINH_COEF));
        } else if (y < 94906265.62) {
            // 94906265.62 = 1/Math.sqrt(EPSILON_SMALL)
            ans = Math.log(y + Math.sqrt(y * y + 1.0));
        } else {
            ans = 0.69314718055994530941723212145818 + Math.log(y);
        }
        if (x < 0.0)
            ans = -ans;
        return ans;
    }

    static double csevl(double x, double coef[]) {
        double b0, b1, b2, twox;
        int i;
        b1 = 0.0;
        b0 = 0.0;
        b2 = 0.0;
        twox = 2.0 * x;
        for (i = coef.length - 1; i >= 0; i--) {
            b2 = b1;
            b1 = b0;
            b0 = twox * b1 - b2 + coef[i];
        }
        return 0.5 * (b0 - b2);
    }
}

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