Sigmoid函数不同于Matlab的结果

Question

如何在Java中编写sigmoid函数？我的hx = [0.51,0.51,0.51,0.51,0.51]输出为sigmoid =[1.6,1.6,1.6,1.6,1.6]，当我在Matlab中执行时，sigmoid的值为[ 0.6248 ,0.6248, 0.6248, 0.6248]：

public double[] sigmoidFunction() {
    int i;
    double[] sigmoid = new double[x_theta.length];
    for(i=0;i<x_theta.length; i++)
        sigmoid[i] = 1 / 1 + StrictMath.exp(-x_theta[i]);

    return sigmoid;
}

Answer 1

你忘记了括号：

sigmoid[i] = 1 / 1 + StrictMath.exp(-x_theta[i]);

相当于

sigmoid[i] = (1 / 1) + StrictMath.exp(-x_theta[i]);

等等

sigmoid[i] = 1 + StrictMath.exp(-x_theta[i]);

，而你似乎需要

sigmoid[i] = 1 / ( 1 + StrictMath.exp(-x_theta[i]) );