OCTOBER, 1988
RECENT MODIFICATIONS IN DYNAMICS

Last June, I decided to bring out a new revision of the
program and documentation, but additional features begged to be
added.

The program now works in color on EGA and VGA screens and
on CGA screens, but for CGA there are only two colors in
addition to black and white. To make full use of the color, you
must have 640 KB memory, though it should run with 512 KB. The
pictures can be stored in color on disk in less space than the
monocrome version reqires.

The menus have been reworked with the goal of putting
simpler information in front of the user by user more menus. As a
result some of the documentation is inaccurate in the description
of the menus. The command descriptions are however hopefully
correct. If a command that you want is not in the menu, then try
it anyway. It is probably still there.

Documentation has been updated drastically, including more
examples and details on how to change the maps and differential
equations (though you must have a Microsoft C compiler).

The stable and unstable manifold routines have been made
more robust as a result of a great deal of detailed study. The
straddle orbit routines have been revised about once a month since
Nusse and I now have algorithms that are both efficient and (in
nice cases) rigorously justifiable. These stable and unstable
routines and straddle routines and basin routines are quite basic
to dynamics would be reasonable material for sophomore dynamics
courses.

Eric Kostelich has put a great deal of effort to make the
source code compatible with UNIX. The UNIX version still has some
rough spots. For example, it is monochrome only, and you cannot
yet store pictures on disk. It has not been thoroughly tested. It
is set up to work in two windows, one a text window for commands
and one a graphics window. The mouse is used only for pointing to
a window. It must point to the graphics window to recognize the
keyboard.

The source code compiles on UNIX computers provided
XWindows Version 11 is available. Some minor changes must be made
in the file YC.H so that it knows X11 commands are appropriate
instead of MS (Microsoft) That includes many SUNS and UNIX
Microvaxes. No support is available yet for mice and the Unix
version does not allow color.

The goal is not to finish the program but to have a
program that can be extended by the user. Since it is constantly
undergoing change, bugs can creep into places that were bug free.
Please report all problems with as much detail as possible,
including the circumstances. I would also like recommendations for
changes. Within the next year I expect it to be published (at low
cost), probably by SIAM. People getting this version are acting as
testors, and their comments would be helpful, though do not expect
a direct response.

Computer programs for studying nonlinear dynamics have
been advertised for $600. I view this program differently, as a
package of ideas that I want to make available to the scientific
community, to as many students and faculty and scientists as
possible. I cannot give help in individual cases. I view this
package of programs and documentation as the equivalent of a
research publication and I would like to request that papers that
use it should acknowledge it as a publication. Others will then
learn about it and will be able to benefit from its use.
Acknowledgements to the program should be in the the references
section and referred to as a book would be. For example,

J.A. Yorke, DYNAMICS, A PROGRAM FOR IBM PC CLONES, University of
Maryland, College Park, 1988.

Several scientists have told me that it is stupid to make
the source code available, but I hope that they miss the point. I
will permit parts of the source code to be included free of charge
in other programs provided permission is obtained in writing from
me and provided acceptable acknowledgements of authorship and
copywrites are included in the new program. I also look foreward
to others writing modules for inclusion in the program, with
acknowlegements of course. In the next version more documentation
will be available for those who want to adapt the program to very
different kinds of projects. For the moment, peruse all the .DOC
files included.

James A. Yorke