   Calculation of output delta's
  Hello,Perhaps someone can shed some light on the delta calculation value.I read James Freeman's book on ANN.The calculation of the delta is : delta = a * (1 - a) * (r  - a) where  a = axon value and r = requested value.But I ran in the problem that whenever the actual/current value is 0 the delta is always 0 too.Is there a better way to calculate the delta's?I cannot be the only person that ran in to this I guess.regards Hans-Peter   
  If I understand correctly,a = 1/(1+exp(some_linear_combination_of_the_inputs))If that's the case, a will be 0 only if the linear combination of the inputs is -infinity, or at least some huge negative number. Stay clear of such numbers and you won't run into trouble. In other words: Perhaps some of your weights are too large.   