function [v,l,r] = fperron(w,f)
%FPERRON Perron-Frobenius eigenvalues
%       and left and right Perron-Frobenius eigenvectors.
%
%       [V,L,R] = FPERRON(W,F) 
%       V = FPERRON(W,F)
%
%       where V contains the P-F eigenvalues of abs(F), L the left P-F 
%       eigenvectors, and R the right P-F eigenvectors. F is an MVFR
%       matrix, and W the associated frequency vector. Each row 
%       in L or R is an eigenvector. V,L and R each have as many rows
%       as there are frequencies in W.

%       P. Phaal, November 1987. Modified by J.M.Maciejowski, 1 Dec 87
%       and 10 Dec 1987.
% Copyright (c) 1987 by GEC Engineering Research Centre & Cambridge Control Ltd

nargs = nargin;
nout = nargout;
error(nargchk(2,4,nargs));
[m,n]=fsize(w,f);
if m~=n,
  error('System is not square. (FPERRON)')
end

x = abs(f);
if nout == 1
  v = fmax(w,feig(w,x));
else
  v = [];  l = [];  r = [];
  nf = length(w);
  [rt,vt] = feig(w,x);
  for i = 1:nf
    [e,index] = sort(diag(fgetf(w,vt,i)));
    v = [v;e(m)];
    rti = fgetf(w,rt,i);        
    r = [r; rti(:,index(m)).'];
    lti = real(inv(rti)); % This should be real.(JMM)
    l = [l;lti(index(m),:)];
  end
end