John Cremona on Tue, 02 Dec 2008 18:27:21 +0100

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Dear pari,

The function idealstar(k,I) for an ideal I in a number field k,
returns an abstract representation of the group (Z_K/I) together with
generators.  using this I can easily form the map from the abstract
group to the concrete one, but what about the inverse?  In other
words, given an element of Z_K coprime to I, how can I express it in
terms of the abstract generators?  is there a function for this, or
has someone else implemented it?

I fully realise that one special case of this is the discrete log
problem for Z/pZ, and am not asking for anything which is very fast,
but I hope I will not have to kist all the lements and check them one
by one.


John Cremona