COSET: a program for deriving and testing merohedral and pseudo-merohedral twin laws

Abstract

COSETis a program written in ISO C99 with POSIX extensions which uses left coset decompositions to determine possible merohedral and pseudo-merohedral twin laws. In addition to a stand-alone program, the code may be compiled as a Python extension module. The program can createSHELXLinstruction files which incorporate the appropriate TWIN and BASF instructions for the possible twin law(s).COSETmay also be directed to execute a locally installed copy of theSHELXLbinary executable to test the candidate twin laws in trial refinements. This facilitates the quick screening and assessment of possible twin laws.