Subject: Re: CCL:Parity checking RAM in PCs

From: [email-masked] (Hinsen Konrad)
Date: Wed, 30 Aug 1995 09:00:04 -0400

The bottom line is this: if you run a calculation on one of the new PCs,
   some number of bits _might_ have been randomly flipped.  My question is
   this:  Is it legitimate to report calculations done on such a computer in a
   scientific journal?

It would be nice to have more accurate data on the probability of
memory errors, but assuming that the numbers you quote are of the
right order of magnitute, I'd probably be willing to take that risk,
and also the other hardware-related stochastic risks, like errors in
disk access. In most situations I can think of, several calculations
of rather similar systems would be done and a large error due to a
stochastic source would be visible (in contrast to errors caused by
systematic hardware failures such as the infamous Pentium bug).

However, one should consider making a statement about hardare (and
software!) used for published work oligatory. It would only add one
sentence to each article and at least give readers a chance to spot
dubious results due to hardware/software problems, even if they are
discovered only much later.

-------------------------------------------------------------------------------
Konrad Hinsen                     | E-Mail: [email-masked]
Departement de chimie             | Tel.: +1-514-343-6111 ext. 3953
Universite de Montreal            | Fax:  +1-514-343-7586
C.P. 6128, succ. A                | Deutsch/Esperanto/English/Nederlands/
Montreal (QC) H3C 3J7             | Francais (phase experimentale)
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From: <[email-masked]>
Date: Wed, 30 Aug 1995 19:14:00 -0400

---------------------------------- Forwarded ----------------------------------
From: Matthew Harbowy at 2812NJLP
Date: 8/30/95 6:49PM
To: [email-masked] at INTERNET
Subject: Re: CCL:Parity checking RAM in PCs
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> this:  Is it legitimate to report calculations done on such a computer in a 
     
             Anyone that has run a long computation can sympathize with the 
             concern that the computation may need to be replicated to show that 
             no error has occured.  However, I am not sure that anyone that has 
             spent long hours in the lab to verify that their experiments are 
             valid will sympathize.  As an experimentalist turned computational, 
             I find it odd that computational people generally believe that the 
             computer hardware, software and the users's design are so perfect 
             that one does not need to replicate an experiment to verify the 
             conclusions.  I know replicating computations can be expensive and 
             boring (so are laboratory experiments), but this is the scientific 
             method.  The only answer that I see is replication, not only for 
             parity errors, but software errors, user errors, Murphy's Law and 
             cosmic rays. Then when you report the hardware, software and error 
             found in the experiment, colleagues might have a clue how to try 
             and duplicate this work.
             
             ------------------------------------
             
             Even if an experiment is performed in duplicate, it is not like 
             experimental work where you might take an 'average' over replicates 
             to determine variation. Sadly, computation work is 'supposed' to be 
             exact- perhaps this says a lot for using monte-carlo approaches 
             where a certain degree of randomness is necessary.
             
             An approach i've only toyed with is parallel monte-carlo where for 
             iterations, you don't force parallel calcualtions running on 
             separate processors to all finish to update a matrix: you update as 
             the results come back and start iterations with partially updated 
             matrices. A well-disciplined algorithm might then take advantage of 
             the inherent randomness of processor assignments across a 
             multi-user, massively parallel supercomputer as a way of bringing 
             'true' randomness into a calculation.
             
             I don't have the whereabouts to run with the idea: It's free to a 
             good home.
             
             matt
             who doesn't speak for the thomas j. lipton company