hill cipher encryption way 1x3 plaintext matrix Can someone help me with a Hill cipher?

When do I have to use: 


1x3 plain text matrix (p1, p2, p3) * 3x3 key matrix 
3x3 key matrix * 3x1 plain text matrix


Or they are both correct?

I tried to search the internet, but found nothing useful.
Both representations are essentially equivalent.  If

$$
\begin{bmatrix} c_1 \\ c_2 \\ c_3 \end{bmatrix}
= \begin{bmatrix} k_{11} &amp; k_{12} &amp; k_{13} \\ k_{21} &amp; k_{22} &amp; k_{23} \\ k_{31} &amp; k_{32} &amp; k_{33} \end{bmatrix}
\cdot \begin{bmatrix} p_1 \\ p_2 \\ p_3 \end{bmatrix},
$$

then, equivalently

$$
\begin{bmatrix} p_1 &amp; p_2 &amp; p_3 \end{bmatrix}
\cdot \begin{bmatrix} k_{11} &amp; k_{21} &amp; k_{31} \\ k_{12} &amp; k_{22} &amp; k_{32} \\ k_{13} &amp; k_{23} &amp; k_{33}
\end{bmatrix}
= \begin{bmatrix} c_1 &amp; c_2 &amp; c_3 \end{bmatrix}.
$$

This is a special case of the general rule that

$$ c = K p \iff p^\top K^\top = c^\top, $$

where $M^\top$ denotes the transpose of the matrix $M$.