negative variance possible since 826ec949084d67926ca81292f575c8138f49ad9a

[shawnlaffan]

Since commit 826ec94, PDL::Stats can return negative variance, and stdev of NA, for some cases due to floating point precision.

perl -MPDL -MPDL::Stats -E'my $x = pdl [(0.001) x 6]; say $x->var; say $x->stdv'
-1.41172157875717e-22
NaN

The easiest solution is to set the variance to zero when it is negative.

Unless there is a better way I'll prep a PR with tests in the next few days.

[mohawk2]

Thanks for the report! Released as 0.855. Adding a test for that behaviour showed that on MacOS (and probably clang) even the previous code was giving stdv of NaN, so I set it to 0 if < 0.