dgh@dgh.Eng.Sun.COM (David Hough) (05/29/91)
The late Derrick Lehmer, emeritus professor at UC Berkeley, was a computer
architect, system designer, system implementer, application programmer and
end user before any of these terms were defined, and in fact before at
least half of the people on comp.arch were born. I audited half a course
from him twenty years ago; I remember that he was a very funny guy but that
most of the undergraduates missed most of the humor.
Anyway instead of complaining about what other people hadn't provided in
hardware or software he provided for himself.
The following reminiscences were posted to the na-net newsletter:
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From: Robert D. Silverman <bs@faron.mitre.org.
David L. Elliott <delliott@CEC2.WUSTL.EDU>
Jim Roth <jroth@allvax.enet.dec.com>
Date: Thu, 23 May 1991 01:49:49 GMT
Subject: D. H. Lehmer
It is with a very great deal of sadness that I must report that D. H. Lehmer
passed away last night.
I am deeply saddened by this loss as Professor Lehmer's work has been a
source of personal inspiration for me. I consider him to be the father
of computational number theory; my major field of interest.
Bob Silverman
Mitre Corporation
Professor Lehmer worked on (among other things) the solution of sets of linear
Diophantine equations via Chinese Remainder Theorem. This involved building
a special-purpose computer which had many "delay lines" (recirculating loops)
of prime-integer length. When the numbers in all of the loops lined up (as in
a Las Vegas slot machine hitting a jackpot) a bell would ring and the data
would be dumped and printed out, then re-loaded into the loops. The first of
these machines was purely mechanical; later on (1965?) he bought surplus
radar delay lines and worked out a purely electronic number-theory machine
along the above lines, which he talked about at UCLA. He claimed that his
technique got answers hundreds of times faster than an IBM 704 would have.
Does anyone know whether he ever got a special VLSI chip built for
such purposes?
David L. Elliott
Washington University
There is a photograph and explanation of Dr. Lehmer's factoring machine
in the Dover book "Recreations in the Theory of Numbers" by Albert Beiler.
This machine had many gear driven wheels which would be halted when sets of
holes in them lined up, triggered by a photocell. It was called a
photoelectric number sieve.
Apparently it was an amazing, though tempermental, device, and was
inadvertantly "jammed" by a local Ham radio operator whose transmissions
triggered the photocell at times.
The book also mentions Lehmer's first factoring machine - a bicycle
sprocket and chain contraption!
Will future generations look back similarly at our current massively
parallel computers doing quantum chromodynamics calculations?
Jim Roth
Digital Equipment Corporation
David.Hough@Eng.Sun.COM dgh@validgh.com na.hough@na-net.ornl.gov