TITLE: Mathematical Notation to Represent Cumulative Sum
QUESTION [8 upvotes]: If I have a vector $x$
$$ x = [x_1, x_2, x_3, \ldots, x_N]$$
Is there any proper mathematical notation that best represents the cumulative sum?
$$ y = [x_1, x_1+x_2, x_1+x_2+x_3, \ldots, x_1+x_2+x_3+\ldots+x_N]$$

REPLY [6 votes]: $y=Ax$ where
\begin{equation}
A=
\begin{bmatrix}
1&0&0&...&0&0 \\
1&1&0&...&0&0 \\
1&1&1&..&0&0  \\
\vdots&\vdots&\vdots&\vdots&\vdots&\vdots \\
1&1&1&...&1&0 \\
1&1&1&...&1&1
\end{bmatrix}
\end{equation}