GitHub user ankurdave opened a pull request:
https://github.com/apache/spark/pull/2439
[SPARK-3578] Fix upper bound in GraphGenerators.sampleLogNormal
GraphGenerators.sampleLogNormal is supposed to return an integer strictly
less than maxVal. However, it violates this guarantee. It generates its return
value as follows:
```scala
var X: Double = maxVal
while (X >= maxVal) {
val Z = rand.nextGaussian()
X = math.exp(mu + sigma*Z)
}
math.round(X.toFloat)
```
When X is sampled to be close to (but less than) maxVal, then it will pass
the while loop condition, but the rounded result will be equal to maxVal, which
will fail the test. For example, if maxVal is 5 and X is 4.9, then X < maxVal,
but `math.round(X.toFloat)` is 5.
Instead of rounding X to the nearest integer, this PR rounds X down using
`math.floor(X).toInt`. This is necessary to enable negative bounds.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/ankurdave/spark SPARK-3578
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/2439.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 #2439
----
commit 16385984ae25e23309d3c5de7cf106a520a4a88d
Author: Ankur Dave <[email protected]>
Date: 2014-09-17T23:14:35Z
Round down in sampleLogNormal to guarantee upper bound
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