TWIN

Tells the program TWIN commands will be given below:


TWIN_nam Name of the TWIN model

Name of the twin model


TWIN_spg  Space Group of domains

Space Group symbol for systematic absences of domain contributions


TWIN_typ  itwin


Type of twin matrices


ITWIN=1

The domains contributing to an observation have indices obtained from the input (h,k,l) by multiplying the vector (hkl) by a real  matrix P, so that (hkl)n = P (hkl). The number of the domains contributing to each observation depends if the resulting indices (hkl)n are integers.


ITWIN=2

The input indices are given w.r.t. the super-lattice. It is supposed that a sub-lattice exist and the orientation of the superlattice could have different orientational domains. Each domain is entered as a matrix relating the superlattice direct cell to the parent sub-lattice.


ITWIN=3

The input indices correspond to the first domain. The orientation of the first domain with respect to a cartesian frame is given by the user as for the other domains. Each domain is given by the orientation in the cartesian frame of each cell parameter a,b, c. Only the direction is needed. The program calculates internally the director cosinus.




Whatever the TWIN model the final matrices act on (hkl) as for ITWIN=1. For ITWIN=2,3 the angular position of the motors are tested for an eventual contribution even if the resulting indices are not integer.


TWIN_mat t11 t12 t13 t21 t22 t...

Matrices (one per domain) describing the domains


TWIN_ubm ubm11 ubm12 ubm13 ubm21..

UB-matrix, needed only for precise determination if itwin=2,3.

Comparison of measured angle positions with calculated for the nearest reflections of other domains (In test stage at present).


TWIN_trf tr11 tr12 tr13 tr21 ...

Transfomation matrix for UB =>  UB-new = UB . TR


TWIN_mac  Name of diffractometer

D9, 6T2,...


TWIN_end

Tells the program that no more twin commands are needed





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