ffmap: embedding of final fields

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

Dear PARI developers,

We have added new functions for dealing with extensions of finite
fields:

For example to embed F_3^5 in F_3^10:

a = ffgen([3,5],'a);
b = ffgen([3,10],'b);
m = ffembed(a, b);

m is a map from F_3^5 to F_3^10

You can use ffmap to apply it (recursively to vectors and polynomials):

minpoly(ffmap(m,a))==minpoly(a)

It is possible to compute the reverse (partial) map using ffinvmap:

r = ffinvmap(m);
ffmap(r,ffmap(m,a)) == a

ffmap(r,b) return [] when it is not defined

It is also possible to compose maps using ffcompomap.

Please test!

Cheers,
Bill