nd4j-common/src/main/java/org/nd4j/linalg/util/BigDecimalMath.java
static public BigDecimal sin(final BigDecimal x) {
        if (x.compareTo(BigDecimal.ZERO) < 0) {
            return sin(x.negate()).negate();
        } else if (x.compareTo(BigDecimal.ZERO) == 0) {
            return BigDecimal.ZERO;
        } else {
            /* reduce modulo 2pi
             */
            BigDecimal res = mod2pi(x);
            double errpi = 0.5 * Math.abs(x.ulp().doubleValue());
            int val = 2 + err2prec(FastMath.PI, errpi);
            MathContext mc = new MathContext(val);
            BigDecimal p = pi(mc);
            mc = new MathContext(x.precision());
            if (res.compareTo(p) > 0) {
                /* pi<x<=2pi: sin(x)= - sin(x-pi)
                 */
                return sin(subtractRound(res, p)).negate();
            } else if (res.multiply(new BigDecimal(2)).compareTo(p) > 0) {
                /* pi/2<x<=pi: sin(x)= sin(pi-x)
                 */
                return sin(subtractRound(p, res));
            } else {
                /* for the range 0<=x<Pi/2 one could use sin(2x)=2sin(x)cos(x)
                 * to split this further. Here, use the sine up to pi/4 and the cosine higher up.
                 */
                if (res.multiply(new BigDecimal(4)).compareTo(p) > 0) {
                    /* x>pi/4: sin(x) = cos(pi/2-x)
                     */
                    return cos(subtractRound(p.divide(new BigDecimal(2)), res));
                } else {
                    /* Simple Taylor expansion, sum_{i=1..infinity} (-1)^(..)res^(2i+1)/(2i+1)! */
                    BigDecimal resul = res;
                    /* x^i */
                    BigDecimal xpowi = res;
                    /* 2i+1 factorial */
                    BigInteger ifac = BigInteger.ONE;
                    /* The error in the result is set by the error in x itself.
                     */
                    double xUlpDbl = res.ulp().doubleValue();
                    /* The error in the result is set by the error in x itself.
                     * We need at most k terms to squeeze x^(2k+1)/(2k+1)! below this value.
                     * x^(2k+1) < x.ulp; (2k+1)*log10(x) < -x.precision; 2k*log10(x)< -x.precision;
                     * 2k*(-log10(x)) > x.precision; 2k*log10(1/x) > x.precision
                     */
                    int k = (int) (res.precision() / Math.log10(1.0 / res.doubleValue())) / 2;
                    MathContext mcTay = new MathContext(err2prec(res.doubleValue(), xUlpDbl / k));
                    for (int i = 1;; i++) {
                        /* TBD: at which precision will 2*i or 2*i+1 overflow?
                         */
                        ifac = ifac.multiply(BigInteger.valueOf(2 * i));
                        ifac = ifac.multiply(BigInteger.valueOf(2 * i + 1));
                        xpowi = xpowi.multiply(res).multiply(res).negate();
                        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 set by the error in x itself.
                     */
                    mc = new MathContext(res.precision());
                    return resul.round(mc);
                }
            }
        } /* sin */
    }
static public BigDecimal sin(final BigDecimal x) {
        if (x.compareTo(BigDecimal.ZERO) < 0) {
            return sin(x.negate()).negate();
        } else if (x.compareTo(BigDecimal.ZERO) == 0) {
            return BigDecimal.ZERO;
        } else {
            /* reduce modulo 2pi
             */
            BigDecimal res = mod2pi(x);
            double errpi = 0.5 * Math.abs(x.ulp().doubleValue());
            int val = 2 + err2prec(FastMath.PI, errpi);
            MathContext mc = new MathContext(val);
            BigDecimal p = pi(mc);
            mc = new MathContext(x.precision());
            if (res.compareTo(p) > 0) {
                /* pi<x<=2pi: sin(x)= - sin(x-pi)
                 */
                return sin(subtractRound(res, p)).negate();
            } else if (res.multiply(new BigDecimal(2)).compareTo(p) > 0) {
                /* pi/2<x<=pi: sin(x)= sin(pi-x)
                 */
                return sin(subtractRound(p, res));
            } else {
                /* for the range 0<=x<Pi/2 one could use sin(2x)=2sin(x)cos(x)
                 * to split this further. Here, use the sine up to pi/4 and the cosine higher up.
                 */
                if (res.multiply(new BigDecimal(4)).compareTo(p) > 0) {
                    /* x>pi/4: sin(x) = cos(pi/2-x)
                     */
                    return cos(subtractRound(p.divide(new BigDecimal(2)), res));
                } else {
                    /* Simple Taylor expansion, sum_{i=1..infinity} (-1)^(..)res^(2i+1)/(2i+1)! */
                    BigDecimal resul = res;
                    /* x^i */
                    BigDecimal xpowi = res;
                    /* 2i+1 factorial */
                    BigInteger ifac = BigInteger.ONE;
                    /* The error in the result is set by the error in x itself.
                     */
                    double xUlpDbl = res.ulp().doubleValue();
                    /* The error in the result is set by the error in x itself.
                     * We need at most k terms to squeeze x^(2k+1)/(2k+1)! below this value.
                     * x^(2k+1) < x.ulp; (2k+1)*log10(x) < -x.precision; 2k*log10(x)< -x.precision;
                     * 2k*(-log10(x)) > x.precision; 2k*log10(1/x) > x.precision
                     */
                    int k = (int) (res.precision() / Math.log10(1.0 / res.doubleValue())) / 2;
                    MathContext mcTay = new MathContext(err2prec(res.doubleValue(), xUlpDbl / k));
                    for (int i = 1;; i++) {
                        /* TBD: at which precision will 2*i or 2*i+1 overflow?
                         */
                        ifac = ifac.multiply(BigInteger.valueOf(2 * i));
                        ifac = ifac.multiply(BigInteger.valueOf(2 * i + 1));
                        xpowi = xpowi.multiply(res).multiply(res).negate();
                        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 set by the error in x itself.
                     */
                    mc = new MathContext(res.precision());
                    return resul.round(mc);
                }
            }
        } /* sin */
    }
Trigonometric sine.

@param x The argument in radians.
@return sin(x) in the range -1 to 1.