Scala arange Flaky test

[lanking520]

Currently, I received several reports from contributors about the failed test they got from CI:

�[31m- arange *** FAILED ***�[0m
�[31m  NaN was not less than or equal to 1.0E-4 (NDArraySuite.scala:353)�[0m

Some problems appeared in the CI:

http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-gpu/detail/PR-14365/7/pipeline/281

http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-gpu/detail/PR-14359/7/pipeline

Thanks @haojin2 @yuxihu reporting these issues

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[andrewfayres]

Likely related to #13816. I'm trying to reproduce it locally.

[andrewfayres]

Reproduces locally by increasing the number of iterations to 10k. Both of the tests that were added will intermittently fail. Looks like start isn't being passed to NDArray.arrange but it's a required parameter.

Tagging the author of the PR @kiendang for his input on this.

[kiendang]

Sorry. I'm taking a look at this.

Looks like start isn't being passed to NDArray.arrange but it's a required parameter.

The value of stop was passed to start in both tests. Those two tests were added to test situations where no value is passed to stop (stop = None). The intended behavior would be what happens when start = 0 and stop = Some(<value passed to start>) as whatever was , e.g NDArray.arange(5) should be the same as NDArray.arange(0, Some(5)).
/~https://github.com/apache/incubator-mxnet/blob/30b1cbc1d862f8c5c1f91d0a9f048aef5771f9de/src/operator/tensor/init_op.h#L202-L205

[kiendang]

Found the issue. The reason is if the two compared arrays are both like [0f] and [0f] then diff and norm will be near 0 resulting in division by zero.
/~https://github.com/apache/incubator-mxnet/blob/6aa8c27a69cafc65eb97c4e077cb399462b617e2/scala-package/core/src/test/scala/org/apache/mxnet/CheckUtils.scala#L27-L32
Solution is if diff is near 0f, i.e < Float.MinPositiveValue just return it instead of dividing by norm