GitHub user dbtsai opened a pull request:
https://github.com/apache/spark/pull/1425
[SPARK-2479][MLlib] Comparing floating-point numbers using relative error
in UnitTests
Floating point math is not exact, and most floating-point numbers end up
being slightly imprecise due to rounding errors. Simple values like 0.1 cannot
be precisely represented using binary floating point numbers, and the limited
precision of floating point numbers means that slight changes in the order of
operations or the precision of intermediates can change the result. That means
that comparing two floats to see if they are equal is usually not what we want.
As long as this imprecision stays small, it can usually be ignored.
See the following famous article for detail.
http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/
For example:
float a = 0.15 + 0.15
float b = 0.1 + 0.2
if(a == b) // can be false!
if(a >= b) // can also be false!
(ps, not all the tests involving floating point comparisons are changed to
use almostEquals)
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/AlpineNow/spark
SPARK-2479_comparing_floating_point
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/1425.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1425
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commit f4da8f4f8693763b4823e36e3d270b74a7ce67bf
Author: DB Tsai <[email protected]>
Date: 2014-07-14T23:24:11Z
Alpine Data Labs
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