U and 3 indices
ASSUMPTIONS MADE:
If no U card is provided, the typical reflection
indices are taken to be 13,11,10. These have the property
of being all positive, with .
DETAILS:
The indices are used by routine SYMUNI to select which
of the possible asymmetric units it will choose. SYMUNI
finds one unit, then transforms it using the space group
symmetry until it contains the given
.
This means that must be properly inside a unit, not on a
face or edge. Routine TRYUNI will give an error if this is
not so.
Note that, although in general the provision of a U card will force the asymmetric unit which you intended, in some cases, notably for tetragonal groups, there are (at least) two ways of chopping reciprocal space into asymmetric units, and the user will not be able to impose one if the program has chosen the other.
EXAMPLE:
U -1,4,5
ROUTINES WHICH READ THE CARDS:
INPUTU reads one U card, and is called by SYMUNI