function y=chsign(x,flag)

% CHSIGN    Change the sign of even or odd indexed samples 
%           in sequence x. The sign of samples in x is changed 
%           alternatively starting with the first sample if 
%           flag=1, and starting with the second one if flag=0.           
%
%           See also: CALHPF

%--------------------------------------------------------
% Copyright (C) 1994, 1995, 1996, by Universidad de Vigo 
%                                                      
%                                                      
% Uvi_Wave 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 2, or (at your option) any      
% later version.                                                           
%                                                                          
% Uvi_Wave 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 Uvi_Wave; see the file COPYING.  If not, write to the Free    
% Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.             
%                                                                          
%       Author: Nuria Gonzalez Prelcic
%       e-mail: Uvi_Wave@tsc.uvigo.es
%--------------------------------------------------------

lx=length(x);
if (flag==1)
   y=(-1).^(1:lx).*x;
else
   y=-(-1).^(1:lx).*x;
end