This distribution of galrep includes the following files:

    galrep.c              C source code
    galrep.h              C header file
    galrep_ecdata.dat     Binary datafile
    galrep_gl2data.dat    Binary datafile

The functionality provided by galrep.c is briefly described in
the header file galrep.h.  For some background on the algorithm,
see http://math.mit.edu/~drew/ImageOfGalois.pdf.  This software
only addresses the problem of computing the mod ell Galois image
of an elliptic curve defined over Q, where ell is prime.  Support
for prime powers and even composite moduli may (or may not) be
added in a future release.

The source code is licensed under GPL version 2.0 or later.

The datafile galrep_ecdata.dat contains precomputed data for elliptic
curves over finite fields of prime order p for p < 4096.  This is not
enough information to reliably compute mod ell galois images for every
elliptic curve over Q, but it will handle most cases and should always be
enough when the mod ell image is surjective.  If there are not enough
primes p available to determine the mod ell Galois within the error
probability specified, the error code GALREP_OUT_OF_PRIMES (-10) will
be returned.  In this case you should either reduce the value of
errbnd (the default is 50, indicating a heuristic error rate of 1 in 2^50),
or better, download galrep_ecdata_big.dat, which contains elliptic curve
data for p < 32768, which has, in every case tested to date, always been
sufficient to achieve an error probability of less than 1 in 2^100.

The datafile galrep_gl2data.dat contains precomputed data relating
to conjugacy classes of subgroups of GL(2,Z/ellZ) for primes ell up to 37.
It has been conjectured that every curve over Q without CM has a surjective
mod ell Galois image for all ell > 37.  If you are interested in computing
mod ell Galois images for ell > 37 (e.g. for curves with CM), you can
doonwload galrep_gl2data_big.dat, which contains data for ell up to 59.

Please send questions and/or bug reports to drew@math.mit.edu.

