function alph=oct_get_alpha(mask,nband,refinecoeff);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Create a parameter (alpha) such that it is 1 at
% the open boundaries and 0 after nband points.
% The all 4 boundaries are considerate open; this
% is the landmask that defines the closed boundaries.
%
% alpha is set to 1 for the 2 first oct_parent points
% for the 2 way nesting
%
%  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) 2004-2006 by Pierrick Penven and Laurent Debreu
%  e-mail:Pierrick.Penven@ird.fr  
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
agulhas=0; %1 :longer sponge on the east boundary
%
[M,L]=size(mask);
[imat,jmat]=meshgrid((1:L),(1:M));
dist=0*mask+inf;

for j=1:M
  if mask(j,1)==1 
    dist=min(cat(3,dist,sqrt((imat-1).^2+(jmat-j).^2)),[],3);
  end
  if mask(j,L)==1
    if  agulhas==1
      dist=min(cat(3,dist,0.3*sqrt((imat-L).^2+(jmat-j).^2)),[],3);
    else
      dist=min(cat(3,dist,sqrt((imat-L).^2+(jmat-j).^2)),[],3);
    end
  end
end
for i=1:L
  if mask(1,i)==1 
    dist=min(cat(3,dist,sqrt((imat-i).^2+(jmat-1).^2)),[],3);
  end
  if mask(M,i)==1 
    dist=min(cat(3,dist,sqrt((imat-i).^2+(jmat-M).^2)),[],3);
  end
end
%
% identical oct_parent grid bathymetry in the first 2 oct_parent cells
%
%nbandfixed = 1+2*refinecoeff;
nbandfixed = 1.5+1.5*refinecoeff;
nbandtot = nbandfixed+nband;
%
% Cosine or linear alpha variations
%
%alph=0.5*(cos(pi*(dist-nbandfixed)/nband)+1);
alph=(nbandtot-dist)/nband;
%
alph(dist<nbandfixed)=1;
alph(dist>nbandtot)=0;
%
return