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Given a set of matrices

$$M = \left\{\begin{bmatrix}1&a\\0&3\end{bmatrix} \mid a \in \mathbb R\right\},$$

what does the notation $A_a^n, n \in \mathbb N$ mean?

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Stock question: in what book/paper did you see these? – J. M. Apr 19 '11 at 16:27
A Romanian high-school textbook. – Paul Manta Apr 19 '11 at 16:29
Your markup was mostly right, but you tried to use curly braces without escaping them. Curly braces are grouping delimiters in $\TeX$, so you need to escape them with a backslash if you mean them literally. Also, it's better to use \mid for the vertical "such that" bar instead of just |, since it's treated as an operator and gives you the appropriate spacing. – joriki Apr 19 '11 at 16:36
Addendum: bmatrix gives bracketed matrices, which is what you seem to want. – J. M. Apr 19 '11 at 16:37
up vote 4 down vote accepted

$A_a$ seems to be a shorthand for a typical matrix in $M$. Then $A_a^n$ is the $n$-th power of $A_a$.

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Yes, it appears that's what it means. Thanks! – Paul Manta Apr 19 '11 at 16:35

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