[Tex/LaTex] an elegant way of indicating repeating elements in a vector

math-mode

Consider a vector that is made up of N times the same element, stacked next to each other. I am having a hard time coming up with an elegant mathematical notation for indicating the repetitiveness of the elements, and the how often they repeat.

The best I could come up with is:

A vector with repeating elements

\documentclass{article}

\usepackage{mathtools}

\begin{document}
\[
    \underbrace{%
        \begin{pmatrix} 
            \Delta t \mathbf{a}_b &  \Delta t \mathbf{a}_b & \cdots & \Delta t
            \mathbf{a}_b 
        \end{pmatrix}%
     }_{N \times (\Delta t \mathbf{a}_b)} 
\]
\end{document}

Can you propose a way to make this clearer in LaTeX?

Best Answer

This is very similar to another answer.

Since the duplication of elements already suggest repetition, I would merely highlight the number of elements/items in the vector:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}

\[
  \bigl( \underbrace{%
    \Delta t \mathbf{a}_b \quad \Delta t \mathbf{a}_b \quad \cdots \quad \Delta t \mathbf{a}_b
  }_{\text{$N$~elements}} \bigr)
\]

\end{document}
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