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https://issues.apache.org/jira/browse/SPARK-2599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14070929#comment-14070929
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DB Tsai commented on SPARK-2599:
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I'm the original guy implementing `almostEquals` for my unit-testing, and I
also noticed that it will be suffering when comparing against 0.0. As [~srowen]
pointed out, it's meaningless to comparing against 0.0 (or a really small
number) with relative error. However, people may just want to write unittest
using relative error for even comparing those small numbers. So I purpose the
following APIs.
`a ~== b +- eps` for relative error, and when a or b near zero, let's say
1e-15, it falls back to absolute error.
`a === b +- eps` which is already in scalatest 2.0 for absolute error, but
since we don't use scalatest 2.0 yet, we build the same APIs in mllib for
absolute error.
> almostEquals mllib.util.TestingUtils does not behave as expected when
> comparing against 0.0
> -------------------------------------------------------------------------------------------
>
> Key: SPARK-2599
> URL: https://issues.apache.org/jira/browse/SPARK-2599
> Project: Spark
> Issue Type: Bug
> Components: MLlib
> Reporter: Doris Xin
> Priority: Minor
>
> DoubleWithAlmostEquals.almostEquals, when used to compare a number with 0.0,
> would always produce an epsilon of 1 >> 1e-10, causing false failure when
> comparing very small numbers with 0.0.
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