OCST update

[A. Scottedward Hodel]

While putting together a short course on controls I've found a few
annoying bugs in the Octave Control Systems Toolbox, which have been
fixed.  An updated toolbox is available at 

    ftp://ftp.eng.auburn.edu/pub/hodel/OCST-ss-981104.tar.gz

This will be the last update to the OCST (I hope) until I finish a rewrite 
that makes use of the list data type in Octave (functions added by John Eaton 
in v. 2.1.8).  The use of lists will aid in an object-oriented interface to
the system data structure, which should make the OCST easier to use and to 
maintain.

Changes to the OCST since the last snapshot are:
    polyout: properly handles complex-coefficients in the input vector
    tf2ss: improved argument checking, fixed row vs column vector bug
    tf2zp: cosmetic changes
    tzero: cosmetic changes
    zgfmul, zgfslv: (used in tzero): rewritten for improved speed; fixed 
        computational bug that sometimes causes balancing (zgpbal) to fail 
        to converge.
    zginit: rewritten for improved speed
    zgpbal: added test for failed convergence.  If generalized CG iteration 
        fails to converge, then zgpbal uses brute force least-squares solution.
    zgsgiv: no longer used in tzero calculations; documentation updated.  Kept 
in
        OCST for backward compatibility.
    zgshsr: checks for length 1 vectors so that zgfslv doesn't have to.
    zp2ssg2: (used in zp2ss, zp2tf): fixed bug in location of complex conjugate 
        pairs and in extraction of two real roots.
    zp2tf: modified to call zp2ssg2; fixes existing bug in zp2tf.

A S Hodel Assoc. Prof. Dept Elect Eng, Auburn Univ,AL  36849-5201
On leave at NASA Marshall Space Flight Center (205) 544-1426