python - 构建 numpy 数组的列 - 为什么第一列仍然全是零？

Question

我不确定在构建数组时我做错了什么。 我做了一些计算，根据这些计算，我完成的数组 z 应该如下所示:

[[  -2.00000000e+000   2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [   2.00000000e+000  -2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]
 [  -2.00000000e+000   2.00000000e+000]]

但我的数组实际上结果是整个第一列为零，如下所示:

[[  5.28650241e-322   2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000  -2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]
 [  0.00000000e+000   2.00000000e+000]]

我不明白我哪里错了。这是我的代码，看起来很简单:

import sys
import numpy as np

def is_class(j, c):
    if j == c:
        return 1
    else: 
        return 0

n = 20
m = 2

weights = np.empty([n,m])
for curr_n in range(n):
    weights[curr_n,:] = 1.0/(n)

beta = np.empty([m,n])
for curr_beta in range(m):
    beta[curr_beta,:] = 1./m

y = np.array([1, 1, 0, 1, 0, 1, 1, 0, 0, 1,1,1,0,0,0,0,0,0,1,1])

# BELOW IS THE PART WHERE THERE MUST BE SOME PROBLEM

for j in range(m):    # computing working responses, z
    z = np.empty([n,m])            
    for i in range(n): 
         # the calculation below is tested and works correctly
         i_class = y[i]
         z[i][j] = (is_class(j,i_class) - beta[j][i])/((beta[j][i])*(1. - beta[j][i]))
         weights[i][j] = beta[j][i]*(1. - beta[j][i]) 
         print z[i,j] # this gives the right value that it ought to have
                      # these values can be compared with the first matrix 
                      # which I put up at the beginning of the question

print "Working responses, z:"
print z # now when I print it out, the first column is suddenly full of zeros

正如您所看到的，我正在计算另一个数组，称为权重，但这似乎没有任何问题。它具有预期的所有行和列。我处理 z 的方式有什么问题？

Answer 1

您将在每个 j 循环步骤中创建一个新数组。所以最后的z只会填最后一行