TITLE: How do you write / represent the 'all ones matrix'?
QUESTION [6 upvotes]: Is there a convention to write the all ones matrix in formulas? I'm going to write about the following formular:
$$
A = B + XD + DX + N
$$
Where D is a diagonal matrix and X the all ones matrix:
$$
X = \begin{pmatrix}
  1 & 1 & \cdots & 1 \\
  1 & 1 & \cdots & 1 \\
  \vdots & \vdots & \ddots & \vdots \\
  1 & 1 & \cdots & 1
 \end{pmatrix}
$$
Is there a greek letter or other convention?

REPLY [5 votes]: Yes, I have seen the $n\times n$ all-ones matrix denoted $J_n$.  I think this is somewhat conventional in algebraic combinatorics, but I have no idea whether it is commonly used elsewhere.