MOP is designed to compute upper bounds for the modality of the action of parabolic subgroups P the Lie algebra of the unipotent radical of P, for simple algebraic groups G.

© Ulf Jürgens, Gerhard Röhrle, October 2001

MOP runs only under GAP 3.4; it is not compatible with GAP 4. It requires the Chevie package.

If you have any questions or problems please email Gerhard Röhrle.


A complete description of what is available in the package can be found in the postscript manual (128 kB).


First you must obtain the file mop-1.1b.tar.gz (81 kB). Once you have this file you can unpack it with the commands

  1. gunzip mop-1.1.tar.gz
  2. tar -xfv mop-1.1.tar

  3. When you do this you should find the following files in a directory called ``pkg/mop'':
    doc/         -MOP documentation
    mop.g        -GAP source
    init.g       -initialization file
    Ideally, MOP should be installed in the GAP packages directory, however, it can be installed anywhere. If MOP is not installed in the GAP packages directory then include suitably edited versions of the following lines
    Add(PKGNAME, "/path/to/directory/containing/pkg/");
    in your .gaprc file in your home directory (create such a file with these lines if you don't already have one).
MOP is now installed and ready to use:
gap> RequirePackage("mop");
gap> r:=Modality("A", 5, []);

Modality analysis for type A5, J = [  ]
A5    1 - 2 - 3 - 4 - 5
416 strings analyzed
205 splittings
72 induction list matches
0 already done
119 occurrences of rank condition
1 J-Height criterion invoked
1 extended operations
1 unresolved strings
characteristic restrictions: [  ]
The modality of P is at most 1.