                             This is file 2VIEW.HLP


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

     This stand-alone program reads two DirAx output files (Xcode.DX1 and
     Xcode.DX2, where "Xcode" stands for a true crystal name) 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, the cells 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
     yield 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 or
     Pentium(R), but somewhat slower if no co-processor is found.

     2View must know the DirAx output files directory (the Xcode.DX1 and
     Xcode.DX2 files). This directory may be given via the command:

     2VIEW DIR

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

     To operate 2VIEW with the correct directory set 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 a corresponding Xcode.DX2
     file is found too, so make sure to (re)name the DirAx output files
     properly.
     If a message like "no files found" appears you did supply a wrong
     directory or one with no matching Xcode.DX1 Xcode.DX2 pairs in it.

     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.

     Mostly more solutions are found, particularly from symmetry within the
     cell. All solutions are geometrically possible and the crystallographer
     must interpret them crystallographically. 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 also from twinning, and to
     complicate matters: both values may be obtained from the same data. In
     general the solution with the smallest rotation is the most interesting
     .
     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)
     [minor revisions 9 April 1996]

