[cctbxbb] Unstable platform-dependent sort order for flex.sort_permutation

[richard.gildea at diamond.ac.uk]

Hi,

I've been trying to diagnose why the miller array cc_anom calculations seem to be platform dependent. I've narrowed this down to a variation in the sort order returned by flex.sort_permutation which is called from within miller.array.sort("packed_indices"). The following code demonstrates the problem and the different output I get on mac and Linux:

Mac:
>>> from scitbx.array_family import flex
>>> a = flex.size_t([7, 1, 1, 5, 1, 3, 3, 7, 1, 7, 3, 3, 5, 7, 5, 5, 5, 1, 1, 1])
>>> print list(flex.sort_permutation(a))
[1, 2, 4, 8, 17, 18, 19, 5, 6, 10, 11, 3, 12, 14, 15, 16, 0, 7, 9, 13]

Linux:
>>> from scitbx.array_family import flex
>>> a = flex.size_t([7, 1, 1, 5, 1, 3, 3, 7, 1, 7, 3, 3, 5, 7, 5, 5, 5, 1, 1, 1])
>>> print list(flex.sort_permutation(a))
[19, 1, 2, 18, 4, 17, 8, 11, 10, 6, 5, 12, 14, 15, 16, 3, 9, 7, 13, 0]

Is it known/expected for the sort order to be platform dependent, or is this a bug?

Here is the relevant code for flex.sort_permutation():

https://github.com/cctbx/cctbx_project/blob/master/scitbx/array_family/sort.h

Cheers,

Richard

Dr Richard Gildea
Data Analysis Scientist
Tel: +441235 77 8078

Diamond Light Source Ltd.
Diamond House
Harwell Science & Innovation Campus
Didcot
Oxfordshire
OX11 0DE

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