Hi, I read a text about crystallography where matrices were designated in the form: (S2 O S1) Where S1 is input coordinate system, S2 is output coordinate system and O is the operator corresponding to the matrix. I found this designation is often more useful than the usual designation by capital letter (which omits information about coordinate systems). Does anyone know whether this designation is used only in crystallography or is it common in mathematics? Does it have a name? Please provide links if possible.