function [ i, j, more ] = index_box2_next_2d ( n1, n2, ic, jc, i, j, more )
%*****************************************************************************80
%
%% INDEX_BOX2_NEXT_2D produces index vectors on the surface of a box in 2D.
%
% Discussion:
%
% The box is has center at (IC,JC), and has half-widths N1 and N2.
% The index vectors are exactly those which are between (IC-N1,JC-N1) and
% (IC+N1,JC+N2) with the property that at least one of I and J
% is an "extreme" value.
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 11 June 2004
%
% Author:
%
% John Burkardt
%
% Input:
%
% integer N1, N2, the half-widths of the box, that is, the
% maximum distance allowed between (IC,JC) and (I,J).
%
% integer IC, JC, the central cell of the box.
%
% integer I, J, the output value of I and J on the previous call.
% Input values ignored on first call.
%
% logical MORE, set this to 0 on the first call, and therafter,
% set it to its output value on the previous call.
%
% Output:
%
% integer I, J, the next index set.
%
% logical MORE, is FALSE (or 0) if there are no more indices
% to return, and TRUE otherwise.
%
if ( ~ more )
more = true;
i = ic - n1;
j = jc - n2;
return
end
if ( i == ic + n1 && j == jc + n2 )
more = false;
return
end
%
% Increment J.
%
j = j + 1;
%
% Check J.
%
if ( jc + n2 < j )
j = jc - n2;
i = i + 1;
elseif ( j < jc + n2 && ( i == ic - n1 || i == ic + n1 ) )
return
else
j = jc + n2;
return
end
return
end