function [k0] = polschur(a,dega)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% [k0]=polschur(a,dega)                                 %
%                                                       %
% MATLAB FUNCTION stabpol IS STABILITY TEST             %
% FOR POLYNOMIAL  a.                                    %
% THE NONZERO POLYNOMIAL  a  IS STABLE IF AND           %
% ONLY IF  k0=0.                                        %
%                                                       %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% S. Pejchova, May  9th,  1994                          %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% preliminary steps and initialization                  %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

k=dega;
k0=0;

if k== -inf
   error('stabpol: Input is zero polynomial');
end

AR=a;
ALF=zeros(2,k+1);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% computing k0                                          %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

for i=1:k
    n=length(AR);
    ALF(1,:)=AR;
    ALF(2,:)=AR(1,n:-1:1);
    al=ALF(1,n)/(ALF(2,n));
    AR=ALF(1,:)-al*(ALF(2,:));

    if AR(1,n) > 1e-15
       error('stabpol: computing error');
    end

    if AR == zeros(1,n)
       break
    end

    AR=AR(1,1:n-1);
    ALF=ALF(:,1:n-1);

    if abs(al) >= 1
       k0=k0+1;
    end
end