Why do sigmoid functions work in Neural Nets?

[apj_anshul]

Hi,

I have just started programming for Neural networks. I am currently working on understanding how a Backpropogation (BP) neural net works. While the algorithm for training in BP nets is quite straightforward, I was unable to find any text on why the algorithm works. More specifically, I am looking for some mathematical reasoning to justify using sigmoid functions in neural nets, and what makes them mimic almost any data distribution thrown at them.

Thanks!

 

[Xitami]

http://www.dspguide.com/ch26.htm