solve_sudoku_init(I)

function simple = solve_sudoku_init(I)
% Function: solve_sudoku_init
%           used for initially solving 9x9 sudoku puzzle
%           basically I split the whole solving procedure into two stages
%           this function is used for the 1st stage
%
% Input: I = 9x9 sudoku puzzle
%        for example: 
%          I = [0 0 0 3 0 1 7 0 0 ; 
%               1 0 0 0 4 0 0 2 0 ;
%               0 6 0 0 0 0 0 5 0 ;
%               9 0 0 4 0 5 0 0 0 ;
%               0 0 6 0 0 0 1 0 0 ;
%               0 0 0 2 0 6 0 8 9 ;
%               0 7 0 0 0 0 4 9 0 ;
%               0 8 0 0 5 0 0 0 2 ;
%               0 0 9 0 0 7 0 0 0 ;]
% Output: simplifier = 9x9 initial solution leaving unsolved grids zeros
%         for example:   
%           simplifier = [0 0 0 3 0 1 7 0 0 ;
%                         1 0 0 5 4 0 0 2 0 ;
%                         0 6 0 0 0 0 0 5 1 ;
%                         9 0 0 4 0 5 2 0 0 ;
%                         0 0 6 0 0 0 1 0 0 ;
%                         0 0 0 2 0 6 0 8 9 ;
%                         0 7 0 0 0 0 4 9 0 ;
%                         0 8 0 0 5 4 0 7 2 ;
%                         0 0 9 0 0 7 0 0 0 ;]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% This is a sub-function of the main function sudoku_yue
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% All copyrights reserved
% By Yue Wu
% 10/05/2009
% ECE Dept, Tufts Univ.
% MA, Medford 02155
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
done = 0;
pre = I;
count = 1;
while ~done
    simple = sudoku_single(pre);
    ind = find(simple==0); %
    test = pre == simple;
    if isempty(ind) == 1 || sum(test(:)) == 81
        done = 1;
    end
    pre = simple;
%     display(['iteration ' num2str(count)]);
%     display(simple);
    count = count+1;
end