java标准偏差数组（我的算法错误）

Question

我是一个初学者，学习如何编程

public static void main()
{
    int array[] = {1,-2,4,-4,9,-6,16,-8,25,-10};
    System.out.print(stdev(array));
}
public static double stdev(int array[])
{
    int stdev = 0;
    int average = 0;
    for(int i = 0; i<array.length;i++)
    {
        average = average+array[i];
    }
    average = average/array.length;
    for(int i = 0; i <array.length;i++)
    {
        stdev = stdev +(array[i]- average)*(array[i]- average);
    }
    return Math.sqrt((double) stdev/(array.length));
}

}

在我的教科书中，它说返回值是11.237，但我得到了10.672。请检查我的java代码。提前谢谢

Answer 1

平均值和标准差应该是双倍的，而不是整数

average = average/array.length;

否则，您将使用int除法，该除法返回一个截断的数字

---

不同之处在于，您的计算应使用Wikipedia article中的“校正标准偏差”。平方根中的分子应为数组的长度-1：

public static double stdev(int array[]) {
  double sum = 0.0;
  for (int i = 0; i < array.length; i++) {
     sum += array[i];
  }
  double average = sum / array.length;

  double sumOfSquares = 0.0;
  for (int i = 0; i < array.length; i++) {
     sumOfSquares += (array[i] - average) * (array[i] - average);
  }

  // **** the issue is below   you need to subtract 1 from array.length ******
  return Math.sqrt(sumOfSquares / (array.length - 1));
}