weird statistics bug in wp34s  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: weird statistics bug in wp34s (/thread245252.html) 
weird statistics bug in wp34s  Andrew Nikitin  06192013 Statistics subsystem does not like certain numbers in Y. For example, 350.33050223 ENTERAttempt to calculate s (standard deviation) gives domain error. This time, the effect is reproducible on emulator.
This is highly numberspecific. Many numbers are breaking it, but many numbers pass through. Without that 3.265E10 it does not give error.
Re: weird statistics bug in wp34s  Walter B  06192013 FWIW, it does return 1.581 and not give any error on the real thing (2.2 2738).
d:)
Re: weird statistics bug in wp34s  Paul Dale  06192013 For each accumulation you made, the value in Y was unchanged so s_{y} should be zero. However, the problem is due to a rounding error during the calculation of s_{y}. Sigma y^{2}  n * (sigma y)^{2} ends up being slightly negative. I'd have preferred to use the robust formulas for this but was hamstrung by the need for backwards compatibility. I've committed a fix which will be in the next firmware revision.
Edited: 19 June 2013, 2:08 a.m.
Re: weird statistics bug in wp34s  Andrew Nikitin  06192013 And what are the robust formulas? Re: weird statistics bug in wp34s  Paul Dale  06192013 Formulas for variance. Specifically, the online algorithm. Recovering the various summation terms we had to support isn't trivial  people expect the usual sums: x, x^{2}, y, y^{2}, xy and all the logarithmic variations. Far easier to just use the traditional method, albeit in double precision for some of the summations.
Re: weird statistics bug in wp34s  Namir  06202013 Thanks for the link Paul. I have been looking for robust algorithms to calculate the mean and standard deviation.
