Re: [WWdevel] Subtractive cancellation

[Arnold P. <ap...@ma...>]

At 08:56 AM 4/12/2006, P. Gavin LaRose wrote:

Hi Davide,

I would vote for keeping the overhead low and the processing as 
simple and straight forward as possible.  Since perl uses double 
precision, errors are quite rare but certainly not so rare that they 
don't show up.  At least they are reasonably understandable to 
someone who knows a little numerical analysis. It's possible a more 
complicated system, in addition to possibly slowing things down, 
might have unanticipated actions which will be harder for people to decipher.

I very much like your idea of providing a numeric stability test.  I 
think the place to put that test would be on the "Edit" problem page 
(maybe renamed to "Edit and Test").  Prof's should have the option of 
testing a problem with a specific seed (usually errors occur for one 
"bad" seed) and also the option of testing on a chosen number of 
random seeds.  Since I assume to use your tests, the problem has to 
load the parser, you could have a bold message that says "Testing 
methods only available to problems using the parser" if used on an 
old problem.  That way more people might be made aware of the 
availability and use of the parser.

Arnie



Prof. Arnold K. Pizer
Dept. of Mathematics
University of Rochester
Rochester, NY 14627
(585) 275-7767