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

[oleg at olexsys.org]

Hi Richard,


it is a bug only if the permutations do not lead to the same sequence. Otherwise you cannot expect to get the same sorting permutations for collections with redundant data on different platforms or even between different versions of compilers.


Cheers,

Oleg.

________________________________
From: cctbxbb-bounces at phenix-online.org <cctbxbb-bounces at phenix-online.org> on behalf of richard.gildea at diamond.ac.uk <richard.gildea at diamond.ac.uk>
Sent: 18 November 2016 14:12:29
To: cctbxbb at phenix-online.org
Subject: [cctbxbb] Unstable platform-dependent sort order for flex.sort_permutation

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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