Function: bnrclass
Section: number_fields
C-Name: bnrclass0
Prototype: GGD0,L,
Help: bnrclass(bnf,ideal,{flag=0}): given a big number field as output by
 bnfinit (only) and an ideal or a 2-component row vector formed by an ideal
 and a list of R1 zeros or ones representing a module, finds the ray class
 group structure corresponding to this module. flag is optional, and can be
 0: default, 1: compute data necessary for working in the ray class group,
 for example with functions such as bnrisprincipal or bnrdisc, without
 computing the generators of the ray class group, or 2: with the generators.
 When flag=1 or 2, the fifth component is the ray class group structure
 obtained when flag=0

