Add row vector to column vector

[Jonathan Seidel]

Hello,
I am starting to learn octave. However I stumbled across the following:

I defined a as a row-vector and b as a column vector. Then I added a + b and 
expected some sort of error message, because the vectors down have the same 
format. However, I received the following answer. Why ?

>> a = [1 2 3]; b = [1; 2; 3];
>> a + b
ans =

   2   3   4
   3   4   5
   4   5   6

Thanks in advance for your help.
Greetings,
Jonathan