abcd — state-space matrices
[A,B,C,D]=abcd(sl)
linear system (syslin list) in state-space or transfer form
real matrices of appropriate dimensions
returns the A,B,C,D matrices from a linear system Sl.
Utility function. For transfer matrices Sl is converted
into state-space form by tf2ss.
The matrices A,B,C,D are the elements 2 to 5 of
the syslin list Sl, i.e. [A,B,C,D] = Sl(2:5) .