elliptic curves with prescribed periods

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

Dear PARI users,

Is there a convenient way to build an elliptic curve with prescribed period in
ellinit Weierstrass form ?
g2=elleisnum(om,4,1);
g3=elleisnum(om,6,1); will give you the curve in the form
y^2 = 4*x^3 - g2*x - g3
and then you will have to do a coordinate change before being able to use ellinit,
which is not very convenient.

Cheers,
Bill.