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Kevin Cowtan wrote:
It seems XPLOR/CNS has only one definition: "from all symmetry
equivalent indices take the one that maximizes H*1024**2 + K*1024 + L"
Yes, I heard this from George Sheldrick, and though it was very elegant.
So to summarise, I like the CNS rule and am happy for it to be used in
files. But I think properly designed software shouldn't care, and may be
subject to other criteria which are more important.
In my Siena tutorial which I think Kevin is quoting, I used a slighlty
more complicated method (so that it would not be thrown by reflections
indices greater than 1023!) but it would have the same effect in practice.
I would like to echo Kevin's last sentence. All SHELX programs use this
method internally but accept reflections in any order, and allow
equivalent reflections and systematic absences to be present. Making a
unique list at the start of the program is a quick and trivial task and
is much more robust than relying on the user to provide a sorted unique
reflection list! If anyone is interested on how to do this I can provide
a copy of my Siena tutorial.
George
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
