>> x = [1, 2, 3]
>> y = [4, 5, 6]
// appending matrix 'y' on the right from matrix 'x' is possible if the two matrices have
// the same number of rows:
>> z1 = [x, y]
matrix columns 1 thru 6
           1             2             3             4             5             6
// stacking matrix 'y' below the matrix 'x' is possible if the two matrices have
// the same number of columns:
>> z2  = [x; y]
           1             2             3
           4             5             6
>>