Subvector matrix notation Is there any notation indicating a subvector of a matrix ? I need to know the correct way of showing it in an academic paper.
i.e: 
Let
$$
A=\begin{bmatrix}
 2& -10 & 0 & 4\\ 
 5&  11 & 8 & -5\\ 
 -9& 3 & -3 & 19
\end{bmatrix}
$$
What's the notation of a vector indicates the first row of matrix A:
$$
??=\begin{bmatrix}
 2& -10 & 0 & 4\\
\end{bmatrix}
$$
And also the notation of a vector indicates the first column of matrix A:
$$
??=\begin{bmatrix}
 2&\\ 
 5&\\ 
 -9&
\end{bmatrix}
$$
 A: Uhm.. In such a case you can just write as following.
Let's say that you want to write down the $i-$ row and the $j-$ column of matrix $A$. Then you can write:


*

*$e_i^T \cdot A,$ where $e_i^T$ is the $i-$ row of the identity matrix.

*$A\cdot e_j$, where $e_j$ is the $j-$ column of the identity matrix. 
A: One notation I have seen uses commas to separate the start and end index and a semi-colon to separate the indices of other dimensions. So in your case
$$
A_{1;1,4} = \begin{bmatrix} 2 & -10 & 0 & 4 \end{bmatrix}
$$
$$
A_{1,3;1} = \begin{bmatrix} 2 \\ 5 \\ 9 \end{bmatrix}
$$
But you could also do something as follows
$$
A_{2,3;2,4} = \begin{bmatrix} 11 & 8 \\ 3 & -3 \end{bmatrix}
$$
Other examples of a similar notation can be seen in this question and here, which seem to add square brackets around the subscript, and omitting the brackets implies that you keep the matrix but with the specified indices removed.
But it is not very common that people need this notation, so if you would use this then it would be good practice to specify what it means according to the notation you used.
