Documentation of fstab

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Function Synopsis

B = fstab(A);

Help text

FSTAB  FSTAB(A) stabilizes a MONIC polynomial with respect to the
   unit circle, i.e. roots whose magnitudes are greater than
   one are reflected into the unit circle.  The result is a monic
   polynomial as well.

Cross-Reference Information

	This function is called by
	armax bj inival iv4 ivar ivstruc oe rarmax rbj roe rpem search searchax searchbj searchoe

Listing of function fstab

function B = fstab(A);

%   L.Ljung 2-10-92
%   Copyright (c) 1986-98 by The MathWorks, Inc.
%   $Revision: 2.3 $  $Date: 1997/12/02 03:43:45 $

if length(A)==1,B=A;return,end
v = roots(A); ind=(abs(v)>eps);
vs = 0.5*(sign(abs(v(ind))-1)+1);
v(ind) = (1-vs).*v(ind) + vs./ (conj(v(ind)));
B = poly(v);
if ~any(imag(A)),B=real(B);end