```
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.
% This library is free software; you can redistribute it and/or
% modify it under the terms of the GNU Library General Public
% License as published by the Free Software Foundation; either
% Version 2 of the License, or (at your option) any later version.
%
% This library 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
% Library General Public License for more details.
%
% You should have received a copy of the GNU Library General Public
% License along with this library; If not, see <http://www.gnu.org/licenses/>.
% Version 2.43
% 23.April 1998
% Copyright (c) 1995-1998 by Alois Schloegl <a.schloegl@ieee.org>
[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;
```

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