Efficient way to construct outer product matrices in MATLAB?

[member 428835]

Suppose we have two vectors $a = [1,2,3]$ and $b = [4,5]$. I want to construct the matrix of products, i.e. $$
\begin{bmatrix}
1\cdot 4 && 1\cdot 5\\
2\cdot 4 && 2\cdot 5\\
3\cdot 4 && 3\cdot 5
\end{bmatrix} =
\begin{bmatrix}
4 && 5\\
8 && 10\\
12 && 15
\end{bmatrix}
$$
Does anyone know an efficient way to do this?

 

[Orodruin]

a' * b

 

[member 428835]

a' * b

Sweet! I was about to write a loop but thought there must be a more efficient way. Thanks! And bummer, if you hadn't used the code template that may have been the shortest character answer in the history of PF!

 

[Orodruin]

It is just regular matrix multiplication. The ' represents the transposed conjugate and so it becomes
$$
\begin{pmatrix}1\\ 2\\ 3\end{pmatrix}
\begin{pmatrix}4& 5\end{pmatrix}
$$
which is what you wanted. MATLAB was constructed for matrix multiplication and manipulation (MATrix LABoratory).

 

[member 428835]

It is just regular matrix multiplication. The ' represents the transposed conjugate and so it becomes
$$
\begin{pmatrix}1\\ 2\\ 3\end{pmatrix}
\begin{pmatrix}4& 5\end{pmatrix}
$$
which is what you wanted. Matlab was constructed for matrix multiplication.

Yep, I totally agree! Maybe my last response was ambiguous; I wasn't asking about your first response, I was complementing how simple it was.