Ankur Dave created SPARK-3578:
---------------------------------
Summary: GraphGenerators.sampleLogNormal sometimes returns
too-large result
Key: SPARK-3578
URL: https://issues.apache.org/jira/browse/SPARK-3578
Project: Spark
Issue Type: Bug
Affects Versions: 1.2.0
Reporter: Ankur Dave
Assignee: Ankur Dave
Priority: Minor
GraphGenerators.sampleLogNormal is supposed to return an integer strictly less
than maxVal. However, it violates this guarantee. It generates its return value
as follows:
{code}
var X: Double = maxVal
while (X >= maxVal) {
val Z = rand.nextGaussian()
X = math.exp(mu + sigma*Z)
}
math.round(X.toFloat)
{code}
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.
A solution is to truncate X instead of rounding it.
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