function [A,B,Q,Z] = qzswitch(i,A,B,Q,Z)
%function [A,B,Q,Z] = qzswitch(i,A,B,Q,Z)
%
% Takes U.T. matrices A, B, orthonormal matrices Q,Z, interchanges
% diagonal elements i and i+1 of both A and B, while maintaining
% Q'AZ' and Q'BZ' unchanged. If diagonal elements of A and B
% are zero at matching positions, the returned A will have zeros at both
% positions on the diagonal. This is natural behavior if this routine is used
% to drive all zeros on the diagonal of A to the lower right, but in this case
% the qz transformation is not unique and it is not possible simply to switch
% the positions of the diagonal elements of both A and B.
% Original file downloaded from:
% http://sims.princeton.edu/yftp/gensys/mfiles/qzswitch.m
% Copyright (C) 1993-2007 Christopher Sims
% Copyright (C) 2008-2011 Dynare Team
%
% This file is part of Dynare.
%
% Dynare 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.
%
% Dynare 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 Dynare. If not, see .
realsmall=sqrt(eps)*10;
%realsmall=1e-3;
a = A(i,i); d = B(i,i); b = A(i,i+1); e = B(i,i+1);
c = A(i+1,i+1); f = B(i+1,i+1);
% A(i:i+1,i:i+1)=[a b; 0 c];
% B(i:i+1,i:i+1)=[d e; 0 f];
if (abs(c)