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Computation of class numbers of number fields. (Calcul du nombre de classes des corps de nombres.) (French) Zbl 0854.11060
Let $$K/k$$ be an extension of number fields. Assume that the quotient $$\zeta_K/ \zeta_k$$ of the Dedekind zeta-function of $$K$$ and that of $$k$$ is homomorphic in the whole complex plane. Note that this assumption holds as soon as $$K/k$$ is normal. We give an expression for the value $$(\zeta_K/ \zeta_k) (1)$$ as the limit of a rapidly convergent series, which makes it convenient to numerically compute this value $$(\zeta_K/ \zeta_k) (1)$$. Our main purpose is to compute relative class numbers of non-abelian CM-fields $$K$$, taking $$k$$ as the maximal totally real subfield of $$K$$ (here $$K/k$$ is quadratic, thus normal). For example, we explain in detail how to compute the relative class number of a non-normal quartic CM-field, and provide tables of relative class numbers of such CM-fields.
The reader may find other illustrations by example of the method developed in this paper in the following two papers [‘Calcul des nombres de classes relatifs: applications aux corps octiques quaternioniques à multiplication complexe’, C. R. Acad. Sci., Paris, Sér. I 317, 643-646 (1993; Zbl 0795.11059), and ‘Calcul des nombres de classes relatifs de certains corps de classes de Hilbert’, ibid. 319, 321-325 (1994; Zbl 0817.11049)].
Reviewer: S.Louboutin (Caen)

##### MSC:
 11R29 Class numbers, class groups, discriminants 11Y40 Algebraic number theory computations 11R42 Zeta functions and $$L$$-functions of number fields
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