Example 4.3 [035L]
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Example 4.3
Let be the split multiplicative torus of rank with coordinates . Then a point of could be visualized by the coordinates and the multiplicative seminorm corresponding to is given by for every Laurent polynomial on . Conversely, every field extension with an absolute value extending the given absolute value on and every give rise to a point by . Note that and are not uniquely determined by .
In particular, we get an inclusion of into . For every , we have . However, there can be also other points with . If , then precisely the points of type 1 (i.e. the -rational points) and the points of type 4 satisfy (see [Be90], 1.4.4).
Returning to the case , there are some distinguished points of which behave completely different than -rational points. For positive real numbers , we define the associated weighted Gauss norm on by
for every Laurent polynomial . It follows from the Gauss Lemma that the weighted Gauss norm is a multiplicative seminorm giving rise to a point . The set is called the skeleton of . Every point satisfies (see [Du12], (0.12) and (0.13)).