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From: adamsf@turing.cs.rpi.edu (Frank Adams)
Newsgroups: comp.ai,talk.philosophy.misc,sci.philosophy.tech
Subject: Re: Algorithms, Turing, Semantics
Message-ID: <-*SBB$@rpi.edu>
Date: 18 Jan 90 05:43:32 GMT
References: <12883@phoenix.Princeton.EDU> <91Eq02wy7eX=01@amdahl.uts.amdahl.com> <4593@convex.UUCP>
Reply-To: adamsf@turing.cs.rpi.edu (Frank Adams)
Organization: RPI CS Dept.
Lines: 28

In article <4593@convex.UUCP> cash@convex.COM (Peter Cash) writes:
>For example, a topographical map can be said to correspond to the terrain
>(I can't bring myself to say that it "approximates" the terrain).  But by
>no stretch of the imagination do the cartographers "algorithms" (his
>procedures and methods), correspond to the terrain.  

Of course they do not.  But then, neither do the maps correspond to my
automobile.

More generally, an algorithm does not, I think, correspond to any particular
object.  It is in the nature of an algorithm to be general.  But an algorithm
plus data can correspond to some physical system, with a more precise
correspondence than just the data has.  For example, consider the programs
meteorologists use, which are fed huge amounts of data, and do even more
computation, producing predictions about the weather.  The data alone
corresponds to the current state of the weather; the data plus program
corresponds to the behavior of the weather.

(As an aside, if one may speak of an algorithm as a process with the
specifics of the situation factored out, as I think one can; and if by
the behavior of a system we mean how it acts in general, not in a particular
instance, which is one of the possible meanings of behavior; then it is
quite legitimate to speak of an algorithm as corresponding to the behavior
of a system.)

Finally, note that when one speaks of a "computer program", one is not
necessarily just talking about [the implementation of] an algorithm; as
much data as desired can be incorporated into the program.