计算Pi

程序：

package pai;

import java.math.BigDecimal;

public class ComplexPi {
    BigDecimal result;

    public ComplexPi(int count) {
        result=new BigDecimal(0);

        for(int i=1;i<=count;i++) {
            result=result.add(getAddedPart(i));
        }
    }

    private BigDecimal getAddedPart(int n) {
        BigDecimal retval=new BigDecimal(1).divide(new BigDecimal(2*n-1), 20, BigDecimal.ROUND_HALF_UP);

        if(n % 2==0) {
            retval=retval.multiply(new BigDecimal(-1));
        }

        return retval;
    }

    public String getPi() {
        return result.multiply(new BigDecimal(4)).toString();
    }

    public static void main(String[] args) {
        ComplexPi cp=new ComplexPi(100000);
        System.out.println(cp.getPi());
    }
}

输出：

3.14158265358979349008

另一个程序：

package pai;

public class SimplePiComputer {
    public static void main(String[] args) {
        double piDivideByFour = 0;

        for(int i = 1;i <= 100000;i++)
        {
            piDivideByFour += Math.pow(-1, i+1) / (2 * i - 1);

        }

        System.out.println("The PI is " + piDivideByFour * 4);
    }
}

结果：

The PI is 3.1415826535897198

参考网页：

1.https://blog.csdn.net/xjlovewjh/article/details/104313648

2.https://www.jianshu.com/p/683b2406342f