repmat(matrix, [repeat_y, repeat_x])

Horizontal

repmat([1 2 3],[1,4])

ans =
 
     1     2     3     1     2     3     1     2     3     1     2     3

Vertical

repmat([1; 2; 3],[4,1])

ans =

     1
     2
     3
     1
     2
     3
     1
     2
     3
     1
     2
     3