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From: ogden@seal.cis.ohio-state.edu (William F Ogden)
Newsgroups: comp.software-eng
Subject: Re: Reusability considered harmful??(!!)
Message-ID: <88689@tut.cis.ohio-state.edu>
Date: 20 Feb 91 18:38:28 GMT
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Reply-To: William F Ogden <ogden@cis.ohio-state.edu>
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Lee writes:
  .....
>Error tolerances will normally be expressed in terms of average or
>RMS and worst-case errors.  They are _not_ going to tell you, "By
>the way, the worst-case negative error is at 44 degrees and the
>worst-case positive error at 46 degrees."  If you are concerned about
>values near 45 degrees, this may well be a problem.  ....

I don't believe that anyone has set out any standards for specifying
reusable numerical software, but it seems unlikely that anything as
simple as worst-case or RMS tolerances would be deemed adequate. Surely
you'd want at least to know an error bound for a sin_approx(x) component as
a function of x. Then you wouldn't have the nasty surprise at 45 degrees.

Numerical software is clearly a domain where you can't pretend that the
names of operations ( e.g. cos, log, etc. ) tell a potential client all
he really needs to know about what they do and where they work. Some
sort of specification standard for this type of software is needed
which takes into account the normal uses of such software -- such as
composing basic operations to make more complex ones. If we don't
figure out how to spec things adequately and just leave potential 
clients to test things out to see what they really do, then they'll
always find it easier to roll their own and reuse will never happen.
/Bill