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Old 01-31-2014, 06:33 AM   #2
rskr
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Location: Santa Fe, NM

Join Date: Oct 2010
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Good numerical analysts and mathematicians do delta epsilon proofs to figure out what a mathematically undefined quantity should be in specific cases to provide continuity, then redefine the definition in a specific instance. For example a correlation between two sets with zero variance, isn't defined, division by zero, but it's pretty obvious that a value of 1.0 or perfect correlation makes the most sense when doing hierarchical clustering.

A more general issue is that using fold changes is likely to amplify noise.
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