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The discriminant of a local field $K$ is the square of the determinant of the matrix $\left( \begin{array}{ccc} \sigma_1(\beta_1) & \cdots & \sigma_1(\beta_n) \\ \vdots & & \vdots \\ \sigma_n(\beta_1) & \cdots & \sigma_n(\beta_n) \\ \end{array} \right)$ where $\sigma_1,..., \sigma_n$ are the embeddings of $K$ into an algebraic closure $\overline{\mathbb{Q}}_p$, and $\{\beta_1, \ldots, \beta_n\}$ is an integral basis for the ring of integers of $K$.

The discriminant of $K$ is an element of $\mathbb{Z}_p$ which is well-defined up to the square of a unit. Thus, it is of the form $p^c u$ where $u$ is a unit. The value $c$ is the discriminant exponent for $K$. Together with the discriminant root field of $K$, it determines the discriminant of $K$ (up to the square of a unit).

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• Last edited by John Cremona on 2018-05-23 14:43:50
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