python - 在日志中遇到无效值
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python - invalid value encountered in log
提问by helix
I have the following expression:
log = np.sum(np.nan_to_num(-y*np.log(a+ 1e-7)-(1-y)*np.log(1-a+ 1e-7)))
我有以下表达式：
log = np.sum(np.nan_to_num(-y*np.log(a+ 1e-7)-(1-y)*np.log(1-a+ 1e-7)))
it is giving me the following warning:
它给了我以下警告：
RuntimeWarning: invalid value encountered in log
log = np.sum(np.nan_to_num(-y*np.log(a+ 1e-7)-(1-y)*np.log(1-a+ 1e-7)))
I don't understand what might be the invalid value or why am I getting it. Any and every help is appreciated.
我不明白什么可能是无效值或为什么我会得到它。任何和每一个帮助表示赞赏。
NOTE: This is a cross-entropy cost function where I added 1e-7to avoid having zeros inside log. y& aare numpy arrays and numpyis imported as np.
注意：这是一个交叉熵成本函数，我在其中添加1e-7以避免日志中出现零。y&a是 numpy 数组并numpy作为np.
回答by Elad Joseph
You probably still have negative values inside the log, which gives nan with real numbers.
您可能在日志中仍然有负值，这为 nan 提供了实数。
aand yshould represent probability between 0 to 1, So you need to check why do you have smaller/larger values there. Adding 1e-7 shows there is something fishy, because np.log(0)gives -inf, which I think is the value you want.
a并且y应该代表 0 到 1 之间的概率，所以你需要检查为什么你有更小/更大的值。添加 1e-7 表明有些可疑，因为np.log(0)给出了-inf，我认为这是您想要的值。
回答by WANG.Zhongzhi
You can use math.log()replacing numpy.log(), which could raise error
您可以使用math.log()替换numpy.log()，这可能会引发错误
>>> import numpy
>>> numpy.log(0)
-inf
>>> numpy.__version__
'1.3.0'
>>> import math
>>> math.log(0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: math domain error
