                             This is file 2VIEW.HLP


                               The Program 2View
                              ===================

     This autonomous program reads two DirAx output files (Xcode.DX1 and
     Xcode.DX2) and looks for rotational relations between the direct lattices.
     If the cell volumes are equal but the cells are not congruent, or if the
     larger cell volume is a multiple of the smaller, they are made congruent
     by a linear transformation. The latter often occurs with DirAx results
     from twins: a main lattice is found from one part of the reflections while
     the rest may give a reciprocal super lattice.

                                Operating 2View
                               -----------------

     You place 2VIEW.EXE in the same directory as DIRAX.EXE by:
     COPY A:2VIEW.EXE C:\DRX\2VIEW.EXE
     The program runs with any type of 80x86/80x87 (co-)processor, but somewhat
     slower if no co-processor is found.

     2View must know the directory for the DirAx output files (the Xcode.DX1
     and Xcode.DX2 files). This is achieved by the command:

     2VIEW DIR

     The program then asks for the directory: as a rule the same you installed
     with DIRAX CHANGE DEFAULTS for the output files, but you may choose
     another containing the relevant files (put there by copying, for example).

     To operate 2View simply type:

     2VIEW

     A list of DirAx Xcode.DX1 output files appears from which you select one.
     Only those Xcode.DX1 files are shown for which an Xcode.DX2 file is found
     as well, so make sure to (re)name the DirAx output files properly.
     If a message like "no files found" appears check if there are no pairs of
     files indeed or supply the correct directory by:

     2VIEW DIR

     The output is rather self-explanatory:
     If necessary A and B are swapped and made congruent first, by transforming
     the cell B to B'. The transformation is expressed by relations between
     (a',b',c') and (a,b,c).
     The rotation axis connecting A and B' is given as components in XYZ, as
     HKL (reciprocal space, a*b*c*) and as uvw (direct space, abc), the
     rotation angle in degrees.
     The relations between HKL in system A and B' are given too.
     NOTE: in earlier versions than the one you are reading now these relations
     were not always correct.

     Sometimes more solutions are found (particularly from symmetry within the
     cell), all geometrically possible, the crystallographer must interpret
     them and decide. Rotation angles of (almost) 180 degrees  m a y  indicate
     twinning with a common axis, small rotations  m a y  originate from two
     fragments, but from twinning too, and to complicate things: both values
     may be obtained from the same data. The solution with the smallest
     rotation is the most interesting, in general.
     A file 2VIEW.LOG is created in the current directory. (You could run the
     program again with a print-out of 2VIEW.LOG within reach.)

     For demonstration you could take the output from EX09 (files EX09.DX1 and
     EX09.DX2), or from EX05 .

     For a guaranteed and quick response:
     e-mail: DUISENBERG@CHEM.RUU.NL

     ---------------------------------------------------------------------
     26 October 1993 - (AJMD)

