X-Message-Number: 8598
Date: Mon, 15 Sep 1997 21:05:25 -0700
From: Peter Merel <>
Subject: Re: CryoNet #8593 - #8595

Thomas Donaldson writes,

>Our nervous system (for some of this you must be a reader of PERIASTRON,
>sorry!) also has a feature which MIGHT be impossible for a Turing machine
>to emulate. The best current ideas about how memory forms (in brains, guys,
>in brains) involve growth of new connections between neurons. This comes
>from actual observations. It may also involve growth of new neurons, including
>in adults (readers of PERIASTRON will know why I say this). 

It occurs to me that you may be confusing the TM concept with another notion,
the Von Neumann machine. I'm very willing to believe there may be biological
mechanisms that a Von Neumann machine can't emulate in reasonable time for
reasons of complexity ... as mentioned previously, there's a whole slew 
of generic problems in NP that we're pretty sure run off the rails on a VN. 
But I'd still need some quantification of the capabilities of the VN in 
question before accepting that a particular computational task would be 
too much for it.

>Question (I'm not fooling, but then I'd want to give this more thought
>before I answered, so I really mean it as a question): the classical Turing
>machine is given a tape, which it moves along marking individual digital
>spaces. If we allow formation of new connections and even new neurons, this
>tape becomes endless not only at both ends but even in the middle. 

Any number of heap management algorithms perform well on infinite 
memories with instantaneous seek times and infinite address spaces :-) But 
your mention of an article on a more general computing model than TMs is 
very interesting - I presume by "floating point" you mean "real", and I
guess this sort of beast might be a model of an Analog Computer. If you can 
dig out a reference, I for one would very much appreciate it.

Peter Merel.

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