Content-type: text/html Man page of X-GEN

X-GEN

Section: X-GEN Commands (1)
Updated: April 2005
Index Return to Main Contents
 

NAME

X-GEN - untwinit  

SYNOPSIS

untwinit [interval]  

DESCRIPTION

"untwinit" is a program to calculate the twinning percentage on an

allegedly merohedrally twinned dataset. It currently works in point group 321, where the twins are (hkl) and (khl). It operates at the level of an X-GEN MULIST.

It calculates the percentage of reflections for which J(hkl) = [ I(hkl) * (1-x) + I(khl) * x ] / (1 - 2 * x) is negative; in varying the twinning-fraction value x, we look a point at which the curve takes off. See R.G.Fisher & R.M.Sweet, _Acta Cryst._ 36: 755 (1980). The MULIST may come in in any order but it's assumed to have only h >=0, k>=0, l >=0. We sort it on sin(theta) so we never have to look very far around a reflection to find its mate.

The program begins by assuming the maximum possible twin fraction is 0.5 and calculates how many J values are negative for each twin fraction between 0 and that maximum fraction. The interval between tested values of x is, by default, 0.005. If the user wishes to use a finer or coarser value, he or she can do so: see below.

interval The interval between twin-fraction values.

The default value is 0.005, so 101 counts are done.
 

EXAMPLES

untwinit Read a MULIST and calculate the twin fraction,

using an interval of 0.005 between calculations of the twin fraction. Thus 101 counts will be performed.

untwinit 0.02 Read a MULIST and calculate the twin fraction,

using an interval of 0.02 between calculations of the twin fraction. Thus 26 calculations will be performed.
 

REPORTING BUGS

Report bugs to Andy Howard at howard@iit.edu or 312-567-5881.  

COPYRIGHT

Copyright © 2002, Illinois Institute of Technology. See the file 'LICENSE' for information on usage and redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES


 

Index

NAME
SYNOPSIS
DESCRIPTION
EXAMPLES
REPORTING BUGS
COPYRIGHT

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Time: 02:08:09 GMT, October 03, 2005