Function: gcharnewprec
Section: number_fields
C-Name: gcharnewprec
Prototype: Gp
Help: gcharnewprec(gc): given a Grossencharacter group \kbd{gc}, recomputes
 its invariants to ensure accurate results to current precision.
Doc: $\var{gc}$ being a Grossencharacter group output by \kbd{gcharinit},
 recomputes its archimedean components ensuring accurate computations to
 current precision.

 It is advisable to increase the precision before computing several
 values at large ideals.
