\\ For T309 this gives the rows with ell = 2, 3, 5, 7, 13, 37.
E = ellmodulareqn(13);
E[2] == 0 \\ true for a canonical equation
E[1]The generator computes exact $q$-expansions of $\mathfrak m_\ell$ and $j$ and finds the one-dimensional rational kernel among the monomials $x^a y^b$ with $0\leq a\leq\ell+1$ and $0\leq b\leq v$, where $v=s(\ell-1)/12$. It truncates beyond the total pole order $v(2\ell+2)$ of such a relation on $X_0(\ell)$, so a relation whose $q$-expansion vanishes that far is identically zero.
Each resulting polynomial is required to have integer coefficients, leading coefficient $1$ in $x^{\ell+1}$, and the expected bidegree; the stored rows were factored over $\mathbb Z[x,y]$ and are irreducible. At $\ell=2,3,5,7,13,37$, where PARI/GP's ellmodulareqn returns type $0$, the rows equal PARI's canonical data. For $\ell=2,3,5,7,11$, the stored classical modular polynomial was found to divide the resultant obtained by eliminating the eta quotient; at $\ell=2,3,5,7$ this resultant equals it up to a constant.