Hi Oleg,

The permutations would lead to the same sequence of miller indices, but in the context of an unmerged reflection array (i.e. miller.array.sort_permutation), then the data associated with those miller indices would not necessarily be in the same order. As the dataset is then split into two half-datasets, this difference in sort order leads to a different value of the calculate correlation coefficient between those two half datasets:

https://github.com/cctbx/cctbx_project/blob/master/cctbx/miller/__init__.py#L4700

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
________________________________
From: cctbxbb-bounces@phenix-online.org [cctbxbb-bounces@phenix-online.org] on behalf of oleg@olexsys.org [oleg@olexsys.org]
Sent: 18 November 2016 15:59
To: cctbx mailing list
Subject: Re: [cctbxbb] Unstable platform-dependent sort order for flex.sort_permutation

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@phenix-online.org <cctbxbb-bounces@phenix-online.org> on behalf of richard.gildea@diamond.ac.uk <richard.gildea@diamond.ac.uk>
Sent: 18 November 2016 14:12:29
To: cctbxbb@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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