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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.
untwinit Read a MULIST and calculate the twin fraction,
untwinit 0.02 Read a MULIST and calculate the twin fraction,