SFTOOLS has a random number generator that produces a uniform
distribution between 0 and 1, which you can than use in different ways.
You could then select all non-centric reflections and asign their phase
as RanU*360.
For the centric reflections you can first set them to the P-variable in
the CALC command which substitutes the restricted phase value for
centric reflections (0 or 90 degrees). Next you can use the random
number to add 180 degrees to half of the centric reflections.
READ in.mtz
CALC col RanU = RAN_U
SELECT NOT CENTRO
CALC P col Phase = col RanU 360 *
SELECT INVERT
CALC col Phase = P
SELECT col RanU > 0.5
CALC col Phase = 180 +
SELECT ALL
WRITE out.mtz
This is clearly advanced use of the CALC/SELECT commands and even I had
to check the help pages, but I thought it was a nice example of the
flexibility.
Bart
Eleanor Dodson wrote:
You can do that to some extent by scattering random atoms about and
calculating phases from them..
Then the centrics will be sensible.
That is how some direct methods programs get their "random starting set"
of phases..
Depends on how flat you want the starting map to be
Eleanor
David Briggs wrote:
Hi y'all.
Excuse that rather "noddy" question, but I've been googling this for
hours now and I've finally lost patience...
How can I generate a random phase set for either a .mtz or .hkl (cns
format) reflection file (if possbile with sensible values for centric
reflections).
That's it.
Thanks in advance,
Dave
--
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David Briggs, PhD.
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www.dbriggs.talktalk.net <http://www.dbriggs.talktalk.net>
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University of Alberta
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