We describe improvements to the subexponential methods for computing the ideal class
group, the regulator and a system of fundamental units in number fields under the
generalized Riemann hypothesis. We use sieving techniques adapted from the number
field sieve algorithm to derive relations between elements of the ideal class group, and
-adic
approximations to manage the loss of precision during the computation of units.
These improvements are particularly efficient for number fields of small degree for
which a speedup of an order of magnitude is achieved with respect to the standard
methods.
Keywords
number fields, ideal class group, regulator, units, index
calculus, subexponentiality