Notation for constant array.

Question

Consider an array whose elements are all the parameter $a$. I can represent it by $(a_i;i \in [1,8])$, but that doesn't really convey that it is a constant matrix. Does this notation make sense $(a;i \in [1,8])$? Also, this notation is too bulky for my work. I was wondering what you think of the very concise notation $a_{[1,8]}$ or even $a_{[8]}$. I'd like to generalize this to constant arrays whose elements might be ordered sets. For example, $(1,b)_{[1,8]}$ would be an array whose elements are all $(1,b)$. What do you think?

Answer 1

Here's one of mathematics' big secrets - you can use whatever notation you like, as long as it's clearly defined and doesn't cause confusion.

As pointed out in a comment, it is common to use $\mathbf{1}_n$ to represent a vector consisting of $n$ elements that are all equal to 1, so writing $a \mathbf{1}_n$ or $a \cdot \mathbf{1}_n$ would work, but even in a formal mathematical paper it wouldn't be taken for granted and so the author would define it before using it. For example,

Let $\mathbf{a}_n = a \cdot \mathbf{1}_n = (a, a, \ldots, a)$ be a vector containing $n$ repetitions of the value $a$.