Function: mfisCM
Section: modular_forms
C-Name: mfisCM
Prototype: G
Help: mfisCM(F): Tests whether the eigenform F is a CM form. The answer
 is 0 if it is not, and if it is, either the unique negative discriminant
 of the CM field, or the pair of two negative discriminants of CM fields,
 this latter case occurring only in weight 1 when the projective image is
 D2=C2xC2, i.e., coded 4 by mfgaloistype.
Doc: Tests whether the eigenform $F$ is a CM form. The answer
 is $0$ if it is not, and if it is, either the unique negative discriminant
 of the CM field, or the pair of two negative discriminants of CM fields,
 this latter case occurring only in weight $1$ when the projective image is
 $D_{2}=C_{2}\times C_{2}$, i.e., coded $4$ by \kbd{mfgaloistype}.
 \bprog
 ? F = mffromell(ellinit([0,1]))[2]; mfisCM(F)
 %1 = -3
 ? mf = mfinit([39,1,-39],0); F=mfeigenbasis(mf)[1]; mfisCM(F)
 %2 = Vecsmall([-3, -39])
 ? mfgaloistype(mf)
 %3 = [4]
 @eprog
