Java-在新方法中实现伯努利数

Question

我在编辑具有Bernoulli numbers的Java中BigRational helper class的现有实现时遇到问题。最初的实现将伯努利数的计算放在Main方法中。我做了一个新课程来返回个别伯努利数的计算。我做错了什么？

import java.math.BigInteger;

public class Bernoulli {

    public static void main(String[] args) {
        int N = 20;
        System.out.println(bern(N));

    }

    public static BigRational bern(int N) {
        BigInteger[][] binomial = new BigInteger[N+1][N+1];
        for (int n = 1; n <= N; n++) binomial[0][n] = BigInteger.ZERO;
        for (int n = 0; n <= N; n++) binomial[n][0] = BigInteger.ONE;
        for (int n = 1; n <= N; n++)
            for (int k = 1; k <= N; k++)
                binomial[n][k] = binomial[n-1][k-1].add(binomial[n-1][k]);

        BigRational[] bernoulli = new BigRational[N+1];
        bernoulli[0] = new BigRational(1, 1);
        bernoulli[1] = new BigRational(-1, 2);
        for (int k = 2; k < N; k++) {
            bernoulli[k] = new BigRational(0, 1);
            for (int i = 0; i < k; i++) {
                BigRational coef = new BigRational(binomial[k + 1][k + 1 - i], 
                        BigInteger.ONE);
                bernoulli[k] = bernoulli[k].minus(coef.times(bernoulli[i]));
            }
            bernoulli[k] = bernoulli[k].divides(new BigRational(k+1, 1));
        }
        return bernoulli[N];
    }
}

我希望这样做才能计算偶数的Zeta function。

我创建的测试方法通过BigDecimal计算此等式的分母。我看到即将出现的问题，我需要将Bernoulli BigRational转换为BigDecimal吗？我可能需要调整我找到的BigRational class。

import java.math.BigDecimal;
import java.math.BigInteger;

public class Test {
    public static void main(String[] args) {
        int N = Integer.parseInt("20");

        // precompute binomial coefficients
        BigInteger[][] binomial = new BigInteger[N+1][N+1];
        for (int n = 1; n <= N; n++) binomial[0][n] = BigInteger.ZERO;
        for (int n = 0; n <= N; n++) binomial[n][0] = BigInteger.ONE;

        // bottom-up dynamic programming
        for (int n = 1; n <= N; n++)
            for (int k = 1; k <= N; k++)
                binomial[n][k] = binomial[n-1][k-1].add(binomial[n-1][k]);


        // now compute Bernoulli numbers
        BigRational[] bernoulli = new BigRational[N+1];
        bernoulli[0] = new BigRational(1, 1);
        bernoulli[1] = new BigRational(-1, 2);
        for (int k = 2; k < N; k++) {
            bernoulli[k] = new BigRational(0, 1);
            for (int i = 0; i < k; i++) {
                BigRational coef = new BigRational(binomial[k + 1][k + 1 - i], 
                        BigInteger.ONE);
                bernoulli[k] = bernoulli[k].minus(coef.times(bernoulli[i]));
            }
            bernoulli[k] = bernoulli[k].divides(new BigRational(k+1, 1));
        }
        BigDecimal n = new BigDecimal(6);
        BigDecimal two = new BigDecimal(2);
        System.out.println(fac(n).multiply(two));
        System.out.println("\u03A0^2");


    }

    public static BigDecimal fac(BigDecimal n) {
        if (n.equals(BigDecimal.ZERO)) {
            return BigDecimal.ONE;
        }
        return n.multiply(fac(n.subtract(BigDecimal.ONE)));
    }

}