Solved by KFrank in post #2 
              
              
                Hello An! 

I haven’t checked the arithmetic precisely, but I believe the following 
is going on: 
A torch.tensor by default uses single-precision (32-bit) floating 
point numbers.  These have approximately 7 decimal places of 
precision.  Your small number, 5.9e-8, is (relative to 1) just on 
the e…