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From: d83_sven_a@tekno.chalmers.se (Sven (Sciz) Axelsson)
Newsgroups: comp.ai.neural-nets
Subject: PDP programs not working for large nets?
Message-ID: <539@tekno.chalmers.se>
Date: 9 Feb 89 12:01:00 GMT
Organization: Chalmers Univ. of Technology, Gothenburg, Sweden
Lines: 48

I and a college of mine are trying to learn something about neural networks
and PDP, and so we wanted to use the PDP programs from 'Explorations...
(PDP Book 3)' as a starting point. 
Instead of running the extremely trivial examples discussed in the books, we
wanted to go for something a little less trivial, using the PA program on a
network 360 units and initial settings as defined as below:

When run (on an IBM AT with 2.5MB memory) this produces the error message

	error 2100: Floating point error: Invalid
	
after which the program exits to DOS. We have assumed that this is caused by
the algoritms used not handling the calculations for nets of this size very
well, or have we done anything wrong? This is what the network definition
looks like:

	definitions:
	nunits 360
	ninputs 180
	noutputs 180
	end
	network:
	%r  180 180 0 180
	end

and we then use a set-up file as the one below where we set lrate to a size
of about 1/180 as suggested in 'Explorations...'

	get network ournet.net
	set dlevel 3
	set lflag 1
	set mode cs 1
	set nepochs 1
	set param lrate .005
	set step cycle

When we excercise ptrain or strain using a suitable training-pattern, we get
the aformentioned error message after a few seconds of processing.
We would very much appreciate if someone could give some explanation of why
this doesn't work or at least confirm that it cannot work. Please answer
promptly, as we must have this information as soon as possible.

+-------------------------+--------------------------------+------------------+
|   Sven Axelsson         |  d83_sven_a@tekno.chalmers.se  |                  |
|   dep:t of Linguistics  |          (^^ best ^^)          |                  |
|   univ. of Gothenburg   |        dlv_sa@hum.gu.se        |                  |
|   SWEDEN                |      usdsa@seguc21.bitnet      |                  |
+-------------------------+--------------------------------+------------------+