Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / tsa-4.2.4 / hup.m

diff --git a/octave_packages/tsa-4.2.4/hup.m b/octave_packages/tsa-4.2.4/hup.m
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+function b=hup(C)
+%HUP(C)        tests if the polynomial C is a Hurwitz-Polynomial.
+%      It tests if all roots lie in the left half of the complex
+%      plane 
+%       B=hup(C) is the same as 
+%       B=all(real(roots(c))<0) but much faster.
+%      The Algorithm is based on the Routh-Scheme.
+%      C are the elements of the Polynomial
+%      C(1)*X^N + ... + C(N)*X + C(N+1).
+%
+%       HUP2 works also for multiple polynomials, 
+%       each row a poly - Yet not tested
+%
+% REFERENCES:
+%  F. Gausch "Systemtechnik", Textbook, University of Technology Graz, 1993. 
+%  Ch. Langraf and G. Schneider "Elemente der Regeltechnik", Springer Verlag, 1970.
+
+%      $Id: hup.m 5090 2008-06-05 08:12:04Z schloegl $
+%      Copyright (c) 1995-1998,2008 by Alois Schloegl <a.schloegl@ieee.org>
+%
+%    This program is free software: you can redistribute it and/or modify
+%    it under the terms of the GNU General Public License as published by
+%    the Free Software Foundation, either version 3 of the License, or
+%    (at your option) any later version.
+%
+%    This program is distributed in the hope that it will be useful,
+%    but WITHOUT ANY WARRANTY; without even the implied warranty of
+%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%    GNU General Public License for more details.
+%
+%    You should have received a copy of the GNU General Public License
+%    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+[lr,lc] = size(c);
+
+% Strip leading zeros and throw away.
+       % not considered yet
+%d=(c(:,1)==0);
+
+% Trailing zeros mean there are roots at zero
+b=(c(:,lc)~=0);
+lambda=b;
+
+n=zeros(lc);
+if lc>3
+       n(4:2:lc,2:2:lc-2)=1;
+end;
+while lc>1               
+       lambda(b)=c(b,1)./c(b,2);
+       b = b & (lambda>=0) & (lambda<Inf);
+       c=c(:,2:lc)-lambda(:,ones(1,lc-1)).*(c*n(1:lc,1:lc-1));
+       lc=lc-1;
+end;