[SystemSafety] Accuracy of COVID modeling code

paul_e.bennett at topmail.co.uk paul_e.bennett at topmail.co.uk
Fri May 22 13:10:20 CEST 2020

On 5/22/2020 at 10:36 AM, "Olwen Morgan" <olwen at phaedsys.com> wrote:
>I agree that choice of algorithm is much more important than 
>compiler optimisations. Indeed, a reliance on compiler optimisations is 
>often, in my experience, a sign of underlying ignorance of relevant 
>numerica algorithms. This is particularly visible when, using an iterative 
>numerical method, one does not pay sufficient - or as is often the 
>case absolutely no - attention to getting good starting values. Another 
>mortal sin is to forget about strict error bounds. Chebyshev 
>always insisted on them and he was one of the founders of modern 
>approximation theory.
>And as regards summing numbers in ascending order of magnitude, 
>yes, it is better than summing them in no particular order, but there 
>still pitfalls for the unwary even when ascending order is used. The 
>best short text on this is, IMHO:
>/Rounding Errors in Algebraic Processes/, J. H. Wilkinson, Dover 
>though it's hard to get hold of and can cost an arm and a leg even 
>when you can find it.

I always found the book "Approximations for Digital Computers" by
C. H. Hastings a handy reference also. ISBN 0-691-07914-5


Paul E. Bennett IEng MIET
Systems Engineer
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