function [ row, col] = randinterval( matrix, count, key) 
[ m, n] = size( matrix) ;
interval1 = floor( m* n /count) + 1;
interval2 = interval1 - 2;
if interval2 == 0  error( '载体太小不能将秘密信息隐藏进去! ') ;
end
rand('seed' , key) ;
a = rand( 1, count) ; 
row = zeros( [ 1 count] ) ;
col = zeros( [ 1 count] ) ; 
r = 1;
c =1;
row( 1, 1) = r;
col( 1, 1) = c;
for i = 2:count
     if a( i) >=0.5
    c = c + interval1;
     else
    c = c + interval2;
     end
  if c > n
    r = r +1;
         if r > m     
             error( '载体太小不能将秘密信息隐藏进去! ') ;
        end
    c = mod( c, n);
     if c ==0
c = 1;
     end
  end
row( 1, i) = r;
col( 1, i) = c;
end