[SciPy-User] int32 overflow and sqrt of -ve number in scipy.stats.wilcoxon

Simon Baldwin simonb@google....
Fri Mar 22 07:43:42 CDT 2013


I have run into two distinct but possibly connected failure modes in
scipy.stats.wilcoxon.  Before bug-reporting, I'd appreciate any
thoughts on these.

The first is an int32 overflow that occurs where a count of data ties
exceeds 46341.  This occurs in my real data set, comprising around
0.7M samples.  The cause is 32-bit counts returned by dfreps() in
futilmodule.c.  Minimal failing demonstration:

import numpy
import scipy.stats
numpy.seterr(all='raise')
# Raises: FloatingPointError: overflow encountered in int_scalars,
morestats.py, line 1242
scipy.stats.wilcoxon([0.1] * 46341)  # 46341^2 > 2^31-1

The second arises from an attempt to take sqrt of a negative number.
Again, this is in wilcoxon data tie handling and occurs in real data.
Demonstration:

import numpy
import scipy.stats
numpy.seterr(all='raise')
# Raises: FloatingPointError: invalid value encountered in sqrt,
morestats.py, line 1244
scipy.stats.wilcoxon([0.1] * 10)

Both on scipy version 0.9, the latest I have access to.  I've taken a
quick look at the 0.11 code for wilcoxon, and didn't notice any
visible functional change.

Thanks.

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