Updates:
Status: Fixed
Labels: -Milestone-Unplanned Milestone-Release2.18
Comment #3 on issue 982 by [email protected]: Optimize the computation of
standard deviations
https://code.google.com/p/ganeti/issues/detail?id=982
Issue 982 asks to improve the computation of the standard
deviation with respect to precission. First note, that the
"usual" statistics for the standard deviation (count, sum,
sum of squares) is less precise than going over the sample
twice: first to compute the mean and then to compute the
sum of the squared differences. (The "usual" statistics
has the problem small differences of large number in the
"sum of squares minus sum squared" part.) However, what
_can_ be improved is the way the summation is made: for
our use, the values to be summed up usually differ only very
little; hence summing them up in a balanced way can improve
precision over linearly summing up. This is what is done
in this patch series.
Klaus Aehlig (4):
Add a utility function to divide lists
Add a balanced version of sum
Change standard deviation by balanced summing
Improve sum statistics
src/Ganeti/Utils.hs | 34 +++++++++++++++++++++++-----------
src/Ganeti/Utils/Statistics.hs | 27 ++++++++++++---------------
2 files changed, 35 insertions(+), 26 deletions(-)
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