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<p>我正在实现一个机器学习算法,它将一个矩阵近似为另外两个矩阵的倍数:V~=WH。W和H是随机初始化的,并且迭代更新,使得WH更像V</p>
<p>在我的代码中,在每次迭代中,我想(I)更新W和H,以及(ii)基于W和H的新值计算一个分数</p>
<p>我的问题是:我用来评分的函数应该只计算一个分数-它<strong>不应该影响V、W或H-但它似乎是这样做的!我不知道为什么函数会影响全局变量-我认为只有在声明<code>global foo</code>等形式时才会发生这种情况。结果是,根据是否在每次迭代时计算得分,计算出的W和H之间存在<strong>小差异</strong>,这没有意义。你知道吗</p>
<p>下面是一些我已经尽可能精简的代码-它没有实现我的算法或做任何有意义的事情,它只是再现了问题,这是有一个小的差异,在计算W的基础上,你是否注释掉了计算分数的行。你知道吗</p>
<p>有人知道为什么这会改变结果吗?你知道吗</p>
<pre><code>import numpy as np
# TRUE, GLOBAL VALUE OF V - should remain the same throughout
V = np.array([[0.0, 4.0, 0.0, 4.0],
[0.0, 0.0, 1.0, 0.0],
[4.0, 0.0, 0.0, 3.0]]).astype(float)
# RANDOM INITIALIZATIONS for two matrices, which are then updated by later steps
W = np.array([[ 1.03796229, 1.29098839],
[ 0.49131664, 0.79759996],
[ 0.66055735, 0.48055734]]).astype(float)
H = np.array([[ 0.06923306, 0.53105902, 1.1715193, 0.58126684],
[ 1.71226543, 0.54797385, 0.70978869, 1.58761463]]).astype(float)
# A small number, which is added at some steps to prevent zero division errors/overflows
min_no = np.finfo(np.float32).eps
# A function which calculates SOME SCORE based on V_input - below is the simplest example that reproduces the error
# This function should ONLY calculate and return a score - IT SHOULD NOT UPDATE GLOBAL VARIABLES!
def score(V_input):
V_input[V_input == 0] = min_no # I believe that THIS LINE may be UPDATING GLOBAL V - but I don't understand why
scr = np.sum(V_input)
return scr
# This function UPDATES the W matrix
def W_update(Vw, Ww, Hw):
WHw = np.matmul(Ww, Hw)
WHw[WHw == 0] = min_no
ratio = np.matmul(np.divide(Vw, WHw), np.transpose(Hw))
return np.multiply(Ww, ratio)
# Repeated update steps
for it in range(10):
# Update step
W = W_update(V, W, H)
# SCORING STEP - A SCORE IS CALCULATED - SHOULD NOT UPDATE GLOBAL VARIABLES
# HOWEVER, IT APPEARS TO DO SO - SMALL DIFFERENCES BETWEEN FINAL W WHEN COMMENTED OUT/NOT COMMENTED OUT
score_after_iteration = score(V)
# THE OUTPUT PRINTED HERE IS DIFFERENT DEPENDING ON WHETHER OR NOT THE SCORING STEP IS COMMENTED OUT - WHY?
print(W[:2,:2]) # Just a sample from W after last iteration
</code></pre>