python - "Divide by zero encountered in log" when not dividing by zero

Question

When I do:

summing += yval * np.log(sigmoid(np.dot(w.transpose(), xi.transpose()))) + (1-yval)* np.log(1-sigmoid(np.dot(w.transpose(), xi.transpose())))

where there is no division, why do I get a "divide by zero encountered in log" error? As a result, summing becomes [nan].

Answer 1

That's the warning you get when you try to evaluate log with 0:

>>> import numpy as np
>>> np.log(0)
__main__:1: RuntimeWarning: divide by zero encountered in log

I agree it's not very clear.

So in your case, I would check why your input to log is 0.

PS: this is on numpy 1.10.4