Dec 6 2005.
  First version of the report

Dec 22, 2005.
  Updated version of the report: a few corrections and minor improvements (Fig.2)

Sep 11, 2007.
  Completely revised version of the report.
  The programs and data are in the "python-programs" subdirecory,
  and in python-programs.zip.
  Outdated versions are kept in the "old" subdirecory.

Apr 11, 2010.
  Updated README. (minor edits)