Github user cestella commented on the issue: https://github.com/apache/incubator-metron/pull/257 The issue around the `StellarScientificTest` change is that merging t-digests is not precisely the same as adding the same data to one t-digest. Whether this is a bug in the t-digest code or whether it's an artifact of the theory, I don't know. Because this test is using low amounts of data, it's prone to a bit of jitter it seems and the compression level specified before isn't sufficient to ensure that the epsilon chosen (1e-2) is sufficient for repeated runs. I tightened up the compression level to 150 (which is still quite sensible) to make sure we can support at least 1e-2 accuracy for normally distributed data across 100 runs of 1000 elements.
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