Function: elleisnum
Section: elliptic_curves
C-Name: elleisnum
Prototype: GLD0,L,p
Help: elleisnum(om,k,{flag=0}): om=[om1,om2] being a 2-component vector
 giving a basis of a lattice L and k an even positive integer, computes the
 numerical value of the Eisenstein series of weight k. When flag is non-zero
 and k=4 or 6, this gives g2 or g3 with the correct normalization

