
// Make newform 2736.2.a.e in Magma, downloaded from the LMFDB on 17 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_2736_a();"
// To make the coeffs of the qexp of the newform in the Hecke field type "qexpCoeffs();"
// To make the newform (type ModFrm), type "MakeNewformModFrm_2736_2_a_e();".
// This may take a long time!  To see verbose output, uncomment the SetVerbose lines below.
// The precision argument determines an initial guess on how many Fourier coefficients to use.
// This guess is increased enough to uniquely determine the newform.
// To make the Hecke irreducible modular symbols subspace (type ModSym)
// containing the newform, type "MakeNewformModSym_2736_2_a_e();".
// This may take a long time!  To see verbose output, uncomment the SetVerbose line below.
// The default sign is -1.  You can change this with the optional parameter "sign".
function ConvertToHeckeField(input: pass_field := false, Kf := [])
    if not pass_field then
        Kf := Rationals();
    end if;
    return [Kf!elt[1] : elt in input];
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_2736_a();"
function MakeCharacter_2736_a()
    N := 2736;
    order := 1;
    char_gens := [1711, 2053, 1217, 1009];
    v := [1, 1, 1, 1];
    // chi(gens[i]) = zeta^v[i]
    assert UnitGenerators(DirichletGroup(N)) eq char_gens;
    F := CyclotomicField(order);
    chi := DirichletCharacterFromValuesOnUnitGenerators(DirichletGroup(N,F),[F|F.1^e:e in v]);
    return MinimalBaseRingCharacter(chi);
end function;

function MakeCharacter_2736_a_Hecke(Kf)
    return MakeCharacter_2736_a();
end function;


function ExtendMultiplicatively(weight, aps, character)
    prec := NextPrime(NthPrime(#aps)) - 1; // we will able to figure out a_0 ... a_prec
    primes := PrimesUpTo(prec);
    prime_powers := primes;
    assert #primes eq #aps;
    log_prec := Floor(Log(prec)/Log(2)); // prec < 2^(log_prec+1)
    F := Universe(aps);
    FXY<X, Y> := PolynomialRing(F, 2);
    // 1/(1 - a_p T + p^(weight - 1) * char(p) T^2) = 1 + a_p T + a_{p^2} T^2 + ...
    R<T> := PowerSeriesRing(FXY : Precision := log_prec + 1);
    recursion := Coefficients(1/(1 - X*T + Y*T^2));
    coeffs := [F!0: i in [1..(prec+1)]];
    coeffs[1] := 1; //a_1
    for i := 1 to #primes do
        p := primes[i];
        coeffs[p] := aps[i];
        b := p^(weight - 1) * F!character(p);
        r := 2;
        p_power := p * p;
        //deals with powers of p
        while p_power le prec do
            Append(~prime_powers, p_power);
            coeffs[p_power] := Evaluate(recursion[r + 1], [aps[i], b]);
            p_power *:= p;
            r +:= 1;
        end while;    
    end for;
    Sort(~prime_powers);
    for pp in prime_powers do
        for k := 1 to Floor(prec/pp) do
            if GCD(k, pp) eq 1 then
                coeffs[pp*k] := coeffs[pp]*coeffs[k];
            end if;
        end for;
    end for;
    return coeffs;
end function;


function qexpCoeffs()
    // To make the coeffs of the qexp of the newform in the Hecke field type "qexpCoeffs();"
    weight := 2;
    raw_aps := [[0], [0], [-2], [0], [0], [2], [-2], [1], [0], [-2], [4], [2], [-6], [4], [0], [-10], [-4], [-2], [12], [0], [-6], [4], [-8], [-6], [-14], [6], [-4], [-20], [-6], [-14], [-12], [0], [6], [4], [-2], [-20], [-10], [-4], [16], [14], [12], [2], [0], [-6], [6], [-24], [-12], [-4], [4], [22], [-26], [24], [18], [-16], [-6], [16], [14], [-16], [6], [-14], [-4], [-26], [20], [-8], [26], [30], [-4], [-6], [0], [-10], [22], [-8], [32], [34], [-36], [-8], [14], [-26], [18], [10], [24], [-22], [0], [10], [-28], [-32], [-6], [10], [6], [16], [8], [-16], [20], [40], [20], [0], [-34], [-22], [4], [22], [20], [22], [-4], [-14], [4], [-46], [-8], [-18], [32], [26], [-36], [-34], [-18], [-4], [8], [18], [4], [16], [-42], [36], [50], [-6], [-10], [20], [12], [30], [6], [32], [32], [22], [-52], [24], [4], [-34], [-26], [2], [38], [52], [30], [30], [-36], [-10], [56], [20], [-6], [24], [6], [26], [-20], [-48], [-38], [-10], [4], [32], [20], [-56], [8], [6], [26], [46], [32], [-46], [0], [-4], [2], [-40], [4], [-2], [-46], [-18], [-28], [50], [-40], [-38], [12], [-26], [-44], [30], [-52], [-34], [16], [-20], [-14], [18], [-16], [-34], [-22], [4], [-22], [-8], [58], [-8], [-28], [-18], [-24], [-6], [34], [-26], [-2], [24], [30], [-20], [58], [26], [-16], [-34], [-56], [-36], [-18], [4], [34], [-50], [-24], [-68], [-8], [66], [24], [-46], [-24], [-10], [18], [-28], [-30], [-64], [12], [6], [18], [-32], [4], [-32], [6], [44], [12], [42], [52], [24], [-30], [-34], [-40], [48], [-12], [-44], [16], [-30], [42], [0], [-64], [-20], [4], [72], [-10], [-50], [72], [2], [-66], [-40], [70], [-4], [6], [-22], [28], [60], [-50], [-30], [6], [52], [30], [70], [52], [-18], [18], [68], [26], [-40], [58], [24], [-32], [-62], [-70], [48], [-72], [0], [64], [-54], [76], [-40], [-30], [-10], [32], [58], [38], [40], [66], [-44], [-14], [-58], [-44], [-26], [4], [-36], [10], [-2], [8], [20], [12], [34], [60], [-22], [40], [-90], [48], [-74], [-78], [-68], [72], [18], [-32], [-32], [50], [38], [-4], [-54], [-2], [-20], [86], [34], [20], [44], [56], [-18], [-10], [14], [16], [56], [-36], [48], [-38], [18], [58], [-8], [-14], [-58], [70], [-4], [-66], [52], [-2], [36], [72], [6], [-20], [42], [-66], [36], [34], [-6], [-40], [-48], [-2], [48], [-82], [78], [48], [4], [52], [10], [-34], [60], [50], [72], [36], [-72], [-10], [56], [94], [36], [-88], [-14], [70], [42], [-18], [30], [8], [-18], [68], [24], [40], [70], [-20], [-24], [58], [54], [-72], [28], [0], [-38], [52], [-14], [-28], [62], [34], [-58], [-36], [66], [-58], [64], [-34], [90], [76], [-80], [34], [-18], [4], [-92], [-22], [-66], [-24], [4], [-2], [24], [14], [2], [48], [-36], [-14], [78], [36], [38], [4], [48]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_2736_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_2736_2_a_e();".
// This may take a long time!  To see verbose output, uncomment the SetVerbose lines below.
// The precision argument determines an initial guess on how many Fourier coefficients to use.
// This guess is increased enough to uniquely determine the newform.
function MakeNewformModFrm_2736_2_a_e(:prec:=1)
    chi := MakeCharacter_2736_a();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(2999) - 1;
    while true do
        trunc_vec := Vector(Kf, [0] cat [f_vec[i]: i in [1..prec]]);
        B := Basis(S, prec + 1);
        S_basismat := Matrix([AbsEltseq(g): g in B]);
        if Rank(S_basismat) eq Min(NumberOfRows(S_basismat), NumberOfColumns(S_basismat)) then
            S_basismat := ChangeRing(S_basismat,Kf);
            f_lincom := Solution(S_basismat,trunc_vec);
            f := &+[f_lincom[i]*Basis(S)[i] : i in [1..#Basis(S)]];
            return f;
        end if;
        error if prec eq maxprec, "Unable to distinguish newform within newspace";
        prec := Min(Ceiling(1.25 * prec), maxprec);
    end while;
end function;


// To make the Hecke irreducible modular symbols subspace (type ModSym)
// containing the newform, type "MakeNewformModSym_2736_2_a_e();".
// This may take a long time!  To see verbose output, uncomment the SetVerbose line below.
// The default sign is -1.  You can change this with the optional parameter "sign".
function MakeNewformModSym_2736_2_a_e( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_2736_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![2, 1]>,<7,R![0, 1]>,<11,R![0, 1]>,<13,R![-2, 1]>],Snew);
    return Vf;
end function;