Compute BigDecimal e^x to a given scale by the Taylor series. - Java java.math

Java examples for java.math:BigDecimal Calculation

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Description

Compute BigDecimal e^x to a given scale by the Taylor series.

Demo Code

/*/*from  ww  w.  ja va  2  s  . co m*/
 * Copyright 2013 Valentyn Kolesnikov
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.java2s;
import java.math.BigDecimal;

public class Main {
    /**
     * Compute e^x to a given scale by the Taylor series.
     * 
     * @param x
     *            the value of x
     * @param scale
     *            the desired scale of the result
     * @return the result value
     */
    private static BigDecimal expTaylor(BigDecimal x, int scale) {
        BigDecimal factorial = BigDecimal.valueOf(1);
        BigDecimal xPower = x;
        BigDecimal sumPrev;

        // 1 + x
        BigDecimal sum = x.add(BigDecimal.valueOf(1));

        // Loop until the sums converge
        // (two successive sums are equal after rounding).
        int i = 2;
        do {
            // x^i
            xPower = xPower.multiply(x).setScale(scale,
                    BigDecimal.ROUND_HALF_EVEN);

            // i!
            factorial = factorial.multiply(BigDecimal.valueOf(i));

            // x^i/i!
            BigDecimal term = xPower.divide(factorial, scale,
                    BigDecimal.ROUND_HALF_EVEN);

            // sum = sum + x^i/i!
            sumPrev = sum;
            sum = sum.add(term);

            ++i;
            Thread.yield();
        } while (sum.compareTo(sumPrev) != 0);

        return sum;
    }
}

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