weird statistics bug in wp34s - Printable Version +- HP Forums (https://archived.hpcalc.org/museumforum) +-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html) +--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html) +--- Thread: weird statistics bug in wp34s (/thread-245252.html) |
weird statistics bug in wp34s - Andrew Nikitin - 06-19-2013 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 number-specific. Many numbers are breaking it, but many numbers pass through. Without that -3.265E-10 it does not give error.
Re: weird statistics bug in wp34s - Walter B - 06-19-2013 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 - 06-19-2013 For each accumulation you made, the value in Y was unchanged so sy should be zero. However, the problem is due to a rounding error during the calculation of sy. Sigma y2 - 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 - 06-19-2013 And what are the robust formulas? Re: weird statistics bug in wp34s - Paul Dale - 06-19-2013 Formulas for variance. Specifically, the on-line algorithm. Recovering the various summation terms we had to support isn't trivial -- people expect the usual sums: x, x2, y, y2, 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 - 06-20-2013 Thanks for the link Paul. I have been looking for robust algorithms to calculate the mean and standard deviation.
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