function [var_rho]=psi2rho(var_psi)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  Transfert a field at psi points to the rho points
%
%  Further Information:  
%  http://www.croco-ocean.org
%  
%  This file is part of CROCOTOOLS
%
%  CROCOTOOLS 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 of the License,
%  or (at your option) any later version.
%
%  CROCOTOOLS 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 this program; if not, write to the Free Software
%  Foundation, Inc., 59 Temple Place, Suite 330, Boston,
%  MA  02111-1307  USA
%
%  Copyright (c) 2002-2006 by Pierrick Penven 
%  e-mail:Pierrick.Penven@ird.fr  
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[M,L]=size(var_psi);
Mp=M+1;
Lp=L+1;
Mm=M-1;
Lm=L-1;
var_rho=zeros(Mp,Lp);
var_rho(2:M,2:L)=0.25*(var_psi(1:Mm,1:Lm)+var_psi(1:Mm,2:L)+...
                       var_psi(2:M,1:Lm)+var_psi(2:M,2:L));
var_rho(1,:)=var_rho(2,:);
var_rho(Mp,:)=var_rho(M,:);
var_rho(:,1)=var_rho(:,2);
var_rho(:,Lp)=var_rho(:,L);
return