Example usage for java.math BigDecimal round

Introduction

In this page you can find the example usage for java.math BigDecimal round.

Prototype

public BigDecimal round(MathContext mc) 

Source Link

Document

Returns a BigDecimal rounded according to the MathContext settings.

Usage

From source file:org.nd4j.linalg.util.BigDecimalMath.java

/**
 * The hyperbolic cosine./*  w  ww  . ja  v a  2s  .c  om*/
 *
 * @param x The argument.
 * @return The cosh(x) = (exp(x)+exp(-x))/2 .
 */
static public BigDecimal cosh(final BigDecimal x) {
    if (x.compareTo(BigDecimal.ZERO) < 0) {
        return cos(x.negate());
    } else if (x.compareTo(BigDecimal.ZERO) == 0) {
        return BigDecimal.ONE;
    } else {
        if (x.doubleValue() > 1.5) {
            /* cosh^2(x) = 1+ sinh^2(x).
             */
            return hypot(1, sinh(x));

        } else {
            BigDecimal xhighpr = scalePrec(x, 2);
            /* Simple Taylor expansion, sum_{0=1..infinity} x^(2i)/(2i)! */
            BigDecimal resul = BigDecimal.ONE;
            /* x^i */
            BigDecimal xpowi = BigDecimal.ONE;
            /* 2i factorial */
            BigInteger ifac = BigInteger.ONE;
            /* The absolute error in the result is the error in x^2/2 which is x times the error in x.
             */

            double xUlpDbl = 0.5 * x.ulp().doubleValue() * x.doubleValue();
            /* The error in the result is set by the error in x^2/2 itself, xUlpDbl.
             * We need at most k terms to push x^(2k)/(2k)! below this value.
             * x^(2k) < xUlpDbl; (2k)*log(x) < log(xUlpDbl);
             */

            int k = (int) (Math.log(xUlpDbl) / Math.log(x.doubleValue())) / 2;
            /* The individual terms are all smaller than 1, so an estimate of 1.0 for
             * the absolute value will give a safe relative error estimate for the indivdual terms
             */
            MathContext mcTay = new MathContext(err2prec(1., xUlpDbl / k));

            for (int i = 1;; i++) {
                /* TBD: at which precision will 2*i-1 or 2*i overflow?
                 */
                ifac = ifac.multiply(new BigInteger("" + (2 * i - 1)));
                ifac = ifac.multiply(new BigInteger("" + (2 * i)));
                xpowi = xpowi.multiply(xhighpr).multiply(xhighpr);
                BigDecimal corr = xpowi.divide(new BigDecimal(ifac), mcTay);
                resul = resul.add(corr);

                if (corr.abs().doubleValue() < 0.5 * xUlpDbl) {
                    break;
                }

            } /* The error in the result is governed by the error in x itself.
              */
            MathContext mc = new MathContext(err2prec(resul.doubleValue(), xUlpDbl));

            return resul.round(mc);

        }
    }
}

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From source file:org.nd4j.linalg.util.BigDecimalMath.java

/**
 * The inverse trigonometric sine./*from   w  ww.j  a  v a  2s. c  o  m*/
 *
 * @param x the argument.
 * @return the arcsin(x) in radians.
 */
static public BigDecimal asin(final BigDecimal x) {
    if (x.compareTo(BigDecimal.ONE) > 0 || x.compareTo(BigDecimal.ONE.negate()) < 0) {
        throw new ArithmeticException("Out of range argument " + x.toString() + " of asin");

    } else if (x.compareTo(BigDecimal.ZERO) == 0) {
        return BigDecimal.ZERO;
    } else if (x.compareTo(BigDecimal.ONE) == 0) {
        /* arcsin(1) = pi/2
         */
        double errpi = Math.sqrt(x.ulp().doubleValue());
        MathContext mc = new MathContext(err2prec(3.14159, errpi));

        return pi(mc).divide(new BigDecimal(2));

    } else if (x.compareTo(BigDecimal.ZERO) < 0) {
        return asin(x.negate()).negate();

    } else if (x.doubleValue() > 0.7) {
        final BigDecimal xCompl = BigDecimal.ONE.subtract(x);
        final double xDbl = x.doubleValue();
        final double xUlpDbl = x.ulp().doubleValue() / 2.;
        final double eps = xUlpDbl / 2. / Math.sqrt(1. - Math.pow(xDbl, 2.));

        final BigDecimal xhighpr = scalePrec(xCompl, 3);
        final BigDecimal xhighprV = divideRound(xhighpr, 4);
        BigDecimal resul = BigDecimal.ONE;
        /* x^(2i+1) */
        BigDecimal xpowi = BigDecimal.ONE;
        /* i factorial */
        BigInteger ifacN = BigInteger.ONE;
        BigInteger ifacD = BigInteger.ONE;

        for (int i = 1;; i++) {
            ifacN = ifacN.multiply(new BigInteger("" + (2 * i - 1)));
            ifacD = ifacD.multiply(new BigInteger("" + i));

            if (i == 1) {
                xpowi = xhighprV;
            } else {
                xpowi = multiplyRound(xpowi, xhighprV);
            }
            BigDecimal c = divideRound(multiplyRound(xpowi, ifacN),
                    ifacD.multiply(new BigInteger("" + (2 * i + 1))));
            resul = resul.add(c);
            /* series started 1+x/12+... which yields an estimate of the sums error
             */

            if (Math.abs(c.doubleValue()) < xUlpDbl / 120.) {
                break;
            }

        }
        /* sqrt(2*z)*(1+...)
         */
        xpowi = sqrt(xhighpr.multiply(new BigDecimal(2)));
        resul = multiplyRound(xpowi, resul);
        MathContext mc = new MathContext(resul.precision());
        BigDecimal pihalf = pi(mc).divide(new BigDecimal(2));
        mc = new MathContext(err2prec(resul.doubleValue(), eps));

        return pihalf.subtract(resul, mc);

    } else {
        /* absolute error in the result is err(x)/sqrt(1-x^2) to lowest order
         */
        final double xDbl = x.doubleValue();
        final double xUlpDbl = x.ulp().doubleValue() / 2.;
        final double eps = xUlpDbl / 2. / Math.sqrt(1. - Math.pow(xDbl, 2.));
        final BigDecimal xhighpr = scalePrec(x, 2);
        final BigDecimal xhighprSq = multiplyRound(xhighpr, xhighpr);
        BigDecimal resul = xhighpr.plus();
        /* x^(2i+1) */
        BigDecimal xpowi = xhighpr;
        /* i factorial */
        BigInteger ifacN = BigInteger.ONE;
        BigInteger ifacD = BigInteger.ONE;

        for (int i = 1;; i++) {
            ifacN = ifacN.multiply(new BigInteger("" + (2 * i - 1)));
            ifacD = ifacD.multiply(new BigInteger("" + (2 * i)));
            xpowi = multiplyRound(xpowi, xhighprSq);
            BigDecimal c = divideRound(multiplyRound(xpowi, ifacN),
                    ifacD.multiply(new BigInteger("" + (2 * i + 1))));
            resul = resul.add(c);

            if (Math.abs(c.doubleValue()) < 0.1 * eps) {
                break;
            }

        }
        MathContext mc = new MathContext(err2prec(resul.doubleValue(), eps));

        return resul.round(mc);

    }
}

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