B=100;

default(seriesprecision, B);


eisen(k)={
  local(be);
  be=bernvec(k/2);
  return(Ser(1-2*k/be[k/2+1]*sum(j=1,B,sigma(j,k-1)*q^j ), q));
}

hecke(se, n, k) =
{
  local(ans,sprec);
  sprec=length(se);
  ans=polcoeff(se, 0, q)*sigma(n, k-1)+O(q^sprec);
  for(j=1, floor(sprec/n)-1,
    divs = divisors(gcd(j, n));
    ans += q^j*sum(jj=1, #divs, divs[jj]^(k-1) * polcoeff(se, j*n/divs[jj]^2,q));
  );
  return(ans+O(q^(floor(sprec/n))));
}

coefs(elt, basi)=
{
  local(m,l);
  l=length(basi);
  m=matrix(l,l,aa,bb,polcoeff(basi[bb], aa, q));
  if(matdet(m)==0, print("Det is 0 ", m); 1/0);
  return((1/m)*(vector(l,h, polcoeff(elt, h, q))~));
}

domat(n, k, bas)=
{
  local(vecs);
  vecs=vector(#bas, h, coefs(hecke(bas[h], n, k),bas));
  return(Mat(vecs));
}

dopoly(n, k, bas)= charpoly(domat(n,k,bas))

delt()=q*eta(q)^24
e4()=eisen(4)
e6()=eisen(6)

/*  bas=[delt()*delt(), delt()*e4()^3]; */