Function: mfatkin
Section: modular_forms
C-Name: mfatkin
Prototype: GGGb
Help: mfatkin(mf,F,Q): computes F|W_Q. Instead of the
 primitive divisor Q | N, one can input a pair [M,A] from mfmatatkin(mf, Q).
Doc: given a modular form space \kbd{mf} and a modular form $F$, returns
 the modular form $F|W_Q$, where $W_Q$ is the Atkink-Lehner involution.
 Instead of the primitive divisor $Q \mid N$, one can input $[M,A]$, where
 \bprog
   M = mfmatatkin(mf, Q, &A);
 @eprog
 \bprog
 ? mf = mfinit([35,2],0); vecF = mfbasis(mf); F = vecF[1];
 ? mfcoefs(F, 4)
 %2 = [0, 3, -1, 0, 3]
 ? wF = mfatkin(mf, 7, F);
 ? mfcoefs(wF, 4)
 %4 = [0, 1, -1, -2, 7]
 ? mQ = mfmatatkin(mf, 7);
 ? mfcoefs(mfatkin(mf, mQ, F), 4)
 %6 = [0, 1, -1, -2, 7]
 @eprog
