Question

标题对我的问题非常自我解释。

我正在尝试编写一个程序来计算用户输入的一组数字的标准偏差这比我预想的要困难得多，为它编写算法一直很痛苦非常感谢任何帮助！

import java.util.Scanner;

public class StandardDeviation {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        double num;
        double total;
        int n;

        System.out.print("First Number: ");
        num = input.nextDouble();

        n = 0;
        total = 0;

        while ( num != -1 ) {

            n++;
            total += num;
            System.out.print("Next Number: ");
            num = input.nextDouble();
        }

        double mean;
        double dev;
        double devn;
        double sqrt;

        mean = total/n;
        dev = (total - mean);
        devn = dev/n;
        sqrt = Math.sqrt(devn);

        System.out.println("N= " +n);
        System.out.println("Total= " +total);
        System.out.println("Mean= " +mean);
        System.out.println("Deviation= " +dev);

        System.out.print("The standard deviation is: " +sqrt);
    }
}

Answer 1

那是因为你的算法错了。您不能通过单独累积样本来计算标准偏差。你还必须积累他们的方格。

像这样：

    n = 0;
    total = 0;
    total_squared = 0;

    while ( num != -1 ) {

        n++;
        total += num;
        total_squared += num*num;
        System.out.print("Next Number: ");
        num = input.nextDouble();
    }

您的解决方案将是：

    mean = total/n;
    stddev = sqrt(total_squared/n - mean*mean);

Answer 2

以下是使用某些样本数据计算标准偏差的方法。

double[] a = {10, 20, 30};
double total = 0;

for (double i : a) {
    total += i;
}

double mean = total/a.length;

double sqTot = 0;
for (double i : a) {
    sqTot += Math.pow((i-mean), 2);
}

System.out.println("Standard deviation " + Math.sqrt(sqTot/a.length));

Answer 3

标准差的公式是错误的。这样做：

n = 0;
total = 0;
total_sq = 0;

while ( num != -1 ) {
    n++;
    total += num;
    total_sq += num*num;
    System.out.print("Next Number: ");
    num = input.nextDouble();
}

对于人口标准差：

mean = total/n;
dev_p = sqrt(total_sq/n - mean*mean);

样本标准偏差：

dev_s = dev_p * n/(n-1);

无法编写标准差Java Code

3 个答案: