[Scilab-Dev] Directed rounding, please

[Eric WALTER]

I would like Scilab to provide us with three command lines:

the first of them would order subsequent rounding to be carried out 
towards +infinity,
the second one would order subsequent rounding to be carried out 
towards -infinity
and the last one would restore standard rounding to the closest double.

This should not be too much work, as all IEEE-754 compliant processors 
feature these types of rounding. It would allow Scilab users to get an 
(admittedly rough) idea of the quality of what they are computing. If 
the results with rounding towards +infinity are about the same as with 
rounding towards -infinity, this of course does not prove that 
everything is OK, but if the results differ widely, then for sure there 
is some trouble brewing. Under some simplifying hypotheses, it is even 
possible to infer an (again rough) estimate of the number of significant 
digits in the results from the magnitude of the discrepancy.

By implementing this simple suggestion, Scilab would go a long way 
towards helping its users assess the quality of their results, and 
improve the way they evaluate critical results if need be. As Matlab 
does not provide its users with such a facility, this would also give 
Scilab another competitive advantage over its main competitor.

Regards,

Eric Walter

PS: Thanks for the nice ScilabTec 2013 Users Day