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| author | cmiller@zippy.cornsilk.net <> | 2006-12-22 15:37:37 -0500 |
|---|---|---|
| committer | cmiller@zippy.cornsilk.net <> | 2006-12-22 15:37:37 -0500 |
| commit | 50726b2322edac8e93489fcb5ef75a5634222d44 (patch) | |
| tree | 1192dea3a5bbb9777291296b2e70e43c87d40abd /BitKeeper | |
| parent | 7aa1e7190d133dd9bbd9ed7e8ef2923497de1167 (diff) | |
| download | mariadb-git-50726b2322edac8e93489fcb5ef75a5634222d44.tar.gz | |
Bug#22555: STDDEV yields positive result for groups with only one row
When only one row was present, the subtraction of nearly the same number
resulted in catastropic cancellation, introducing an error in the
VARIANCE calculation near 1e-15. That was sqrt()ed to get STDDEV, the
error was escallated to near 1e-8.
The simple fix of testing for a row count of 1 and forcing that to yield
0.0 is insufficient, as two rows of the same value should also have a
variance of 0.0, yet the error would be about the same.
So, this patch changes the formula that computes the VARIANCE to be one
that is not subject to catastrophic cancellation.
In addition, it now uses only (faster-than-decimal) floating point numbers
to calculate, and renders that to other types on demand.
Diffstat (limited to 'BitKeeper')
| -rw-r--r-- | BitKeeper/etc/collapsed | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/BitKeeper/etc/collapsed b/BitKeeper/etc/collapsed index ddaafba882c..837a8997495 100644 --- a/BitKeeper/etc/collapsed +++ b/BitKeeper/etc/collapsed @@ -19,3 +19,4 @@ 454f8960jsVT_kMKJtZ9OCgXoba0xQ 4554a95d7txO1DuO9G3nAizI3SkFAA 4554b3722d71SbPiI2Gx-RhbZjmuIQ +45771031yRCoM_ZfONdYchPvVEgLRg |