Definition:Eventually Periodic P-adic Expansion
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Definition
Let $\struct {\Q_p, \norm {\,\cdot\,}_p}$ be the $p$-adic numbers for some prime $p$.
Let $x \in \Q_p$.
Let $\ldots d_n \ldots d_2 d_1 d_0 . d_{-1} d_{-2} \ldots d_{-m}$ be the canonical expansion of $x$.
Let there be a finite sequence of $k$ digits of $x$:
- $\tuple {d_{r + k - 1} \ldots d_{r+1} d_r }$
such that $r \ge 0$ and for all $n \in \Z_{\ge 0}$ and for all $j \in \set {0, 2, \ldots, k - 1}$:
- $d_{r + j + n k} = d_{r + j}$
where $k$ is the smallest $k$ to have this property.
That is, let the canonical expansion of $x$ be of the form:
- $\ldots d_{r + k - 1} \ldots d_{r+1} d_r d_{r + k - 1} \ldots d_{r+1} d_r d_{r + k - 1} \ldots d_{r+1} d_r \ldots d_2 d_1 d_0 . d_{-1} d_{-2} \ldots d_{-m}$
That is, $\tuple {d_{r + k - 1} \ldots d_{r+1} d_r }$ repeats.
Then the canonical expansion of $x$ is said to be eventually periodic.
Also see
Sources
- 2007: Svetlana Katok: p-adic Analysis Compared with Real ... (previous) ... (next): $\S 1.6$ The $p$-adic expansion of rational numbers: Theorem $1.38$