Does backprop need the derivative ??

[Marwan Jabri]

As the intention of the inquirer is the analog implementation of
backprop, I see two problems: 1- the question whether the derivative can
be replaced by a constant, and more importantly 2- whether the precision
of the analog implementation will be high enough for backprop to work.

Regarding (1), it is likely as Scott Fahlman suggested any derivative that
"preserves" the error sign may do the job. The question however is the
implication in terms of convergence speed, and the comparison thereof with
perturbation type training methods.

Regarding (2), there has been several reports indicating that
backpropagation simply does not work when the number of bits is reduced
towards 6-8 bits! 

	Marwan

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Marwan Jabri			       Email: marwan at sedal.su.oz.au
Senior Lecturer				      Tel: (+61-2) 692-2240
SEDAL, Electrical Engineering,		      Fax:         660-1228
Sydney University, NSW 2006, Australia     Mobile: (+61-18) 259-086