Re: left-right (up-down) parsing may lead to over/underflow of prod

[Rolf Fabian]

> Datum: Wed, 23 Apr 2008 07:20:33 +0200
> Von: "Jaroslav Hajek" <address@hidden>
> An: "Octave Maintainers List" <address@hidden>
> CC: "David Bateman" <address@hidden>, "Rolf Fabian" <address@hidden>
> Betreff: Re: left-right (up-down) parsing may lead to over/underflow of prod

> I've committed `safeprod' to OctaveForge (main/general).
> 
> -- 
> RNDr. Jaroslav Hajek
> computing expert
> Aeronautical Research and Test Institute (VZLU)
> Prague, Czech Republic
> url: www.highegg.matfyz.cz


You should withdraw and remove 'safeprod.m' as soon as possible
because it is a mess and far away from beeing safe in contradiction
to its name.

1) Its help part is corrupted and not understandable.
2) If input is a row vector no product is formed
3) It returns NaNs where not appropriate
   e.g. safeprod([realmax;2]) |- ans = NaN
   whereas Octave:> prod([realmax;2]) = Inf
   gives already the correct answer whereas
   your 'improvement' fails!
   Similar for e.g. :> safeprod([realmax;2i]) |- ans = NaN
   whereas prod gives correct ans = 0 + Infi   
4) It is easy to construct input which leads to
   under/overflow of your 'safeprod' function.
   Hence it is not 'safe'.
5) Weird things may be returned from 'safeprod'
   for complex input containing some Inf, -Inf, Infi
   entries.

I summarize that your function seems to be a nice little
trial to work around the prod bug, but unfortunately it
is not able to remove it completely and thus useless.

R:


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