Solved by KFrank in post #6 
              
              
                Hi Simon! 

Okay, this makes more sense. 
The input and target passed to binary_cross_entropy() 
are both supposed to be probabilities, that is, numbers between 
0 and 1 (with singularities occurring at 0 and 1). 
Your target contains negative numbers, which are not valid 
probabilities. 
(Because y…