
// Make newform 1920.2.h.e in Magma, downloaded from the LMFDB on 28 December 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1920_h();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_1920_h_Hecke();"
// To make the coeffs of the qexp of the newform in the Hecke field type "qexpCoeffs();"
// To make the newform (type ModFrm), type "MakeNewformModFrm_1920_2_h_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_1920_2_h_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
        poly := [1, 0, 3, 0, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [1, 1, 1, 0], [0, 2, 0, 1], [-1, 1, -1, 0]];
    Rf_basisdens := [1, 1, 1, 1];
    Rf_basisnums := ChangeUniverse([[z : z in elt] : elt in Rf_num], Kf);
    Rfbasis := [Rf_basisnums[i]/Rf_basisdens[i] : i in [1..Degree(Kf)]];
    inp_vec := Vector(Rfbasis)*ChangeRing(Transpose(Matrix([[elt : elt in row] : row in input])),Kf);
    return Eltseq(inp_vec);
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_1920_h();"
function MakeCharacter_1920_h()
    N := 1920;
    order := 2;
    char_gens := [511, 901, 641, 1537];
    v := [1, 2, 1, 2];
    // 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;

// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_1920_h_Hecke();"
function MakeCharacter_1920_h_Hecke(Kf)
    N := 1920;
    order := 2;
    char_gens := [511, 901, 641, 1537];
    char_values := [[-1, 0, 0, 0], [1, 0, 0, 0], [-1, 0, 0, 0], [1, 0, 0, 0]];
    assert UnitGenerators(DirichletGroup(N)) eq char_gens;
    values := ConvertToHeckeField(char_values : pass_field := true, Kf := Kf); // the value of chi on the gens as elements in the Hecke field
    F := Universe(values);// the Hecke field
    chi := DirichletCharacterFromValuesOnUnitGenerators(DirichletGroup(N,F),values);
    return chi;
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]];
    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, 0, 0], [0, 1, 1, 0], [0, 0, -1, 0], [0, 0, -2, 0], [0, -2, 0, 2], [0, 1, 0, -1], [0, -1, 2, -1], [0, 1, 4, 1], [2, -2, 0, 2], [0, 2, 6, 2], [0, -1, 6, -1], [4, 3, 0, -3], [0, -2, 4, -2], [0, 3, 6, 3], [-2, -2, 0, 2], [0, 2, 2, 2], [-4, -2, 0, 2], [10, 2, 0, -2], [0, 1, 10, 1], [-4, 0, 0, 0], [2, -2, 0, 2], [0, 5, 2, 5], [8, 3, 0, -3], [0, 2, -4, 2], [-10, -2, 0, 2], [0, -6, -10, -6], [0, 2, -2, 2], [12, 1, 0, -1], [6, -4, 0, 4], [0, -9, -10, -9], [0, 0, -10, 0], [-12, -8, 0, 8], [0, 7, 10, 7], [0, 5, 8, 5], [0, 0, -10, 0], [0, -1, -2, -1], [-8, -3, 0, 3], [0, -1, -2, -1], [2, -4, 0, 4], [0, 2, 18, 2], [-4, 2, 0, -2], [6, 6, 0, -6], [-12, -2, 0, 2], [-2, 4, 0, -4], [0, 0, -10, 0], [0, -3, -14, -3], [0, -3, 4, -3], [0, 4, -2, 4], [-16, -3, 0, 3], [10, 4, 0, -4], [0, 3, 6, 3], [-16, -6, 0, 6], [18, 4, 0, -4], [-8, -2, 0, 2], [0, 1, 2, 1], [14, 8, 0, -8], [0, 0, -14, 0], [0, -5, -22, -5], [4, 7, 0, -7], [0, -2, 8, -2], [0, 1, 10, 1], [0, 6, 22, 6], [0, 9, 6, 9], [20, 0, 0, 0], [14, 8, 0, -8], [0, -8, 2, -8], [0, 1, -4, 1], [10, -2, 0, 2], [12, -1, 0, 1], [-22, 4, 0, -4], [0, -1, 6, -1], [24, 6, 0, -6], [0, -14, -10, -14], [-24, -11, 0, 11], [0, -3, 12, -3], [-2, 4, 0, -4], [0, -4, 2, -4], [4, -5, 0, 5], [0, 12, 20, 12], [22, 6, 0, -6], [-32, -4, 0, 4], [-22, -14, 0, 14], [-28, 0, 0, 0], [6, 10, 0, -10], [0, -7, 2, -7], [24, 7, 0, -7], [0, 4, -24, 4], [22, 6, 0, -6], [0, 2, 6, 2], [0, 10, 6, 10], [-12, 7, 0, -7], [0, 10, 0, -10], [0, 2, -10, 2], [20, 0, 0, 0], [0, -3, 8, -3], [14, 8, 0, -8], [0, -14, -14, -14], [0, 0, 20, 0], [0, 7, 10, 7], [6, 10, 0, -10], [0, -13, -10, -13], [0, -18, -22, -18], [28, 13, 0, -13], [0, 4, -24, 4], [0, -7, -20, -7], [2, -10, 0, 10], [-4, -7, 0, 7], [0, -1, 6, -1], [24, -6, 0, 6], [-38, 2, 0, -2], [0, -2, 6, -2], [12, -1, 0, 1], [0, 1, 2, 1], [0, -7, -24, -7], [0, 3, -6, 3], [0, 14, 20, 14], [0, 3, -10, 3], [10, -8, 0, 8], [0, -2, 30, -2], [12, 2, 0, -2], [-38, -2, 0, 2], [-10, -6, 0, 6], [0, 10, 2, 10], [36, 1, 0, -1], [0, 13, 8, 13], [0, 8, -10, 8], [10, 0, 0, 0], [24, -4, 0, 4], [0, -6, 30, -6], [-12, -1, 0, 1], [0, -7, 8, -7], [-14, 6, 0, -6], [0, -13, -26, -13], [28, 11, 0, -11], [0, 0, -20, 0], [-18, -10, 0, 10], [0, 0, 46, 0], [0, 3, 2, 3], [0, -4, 18, -4], [0, -14, 0, -14], [0, 1, 40, 1], [0, 8, 38, 8], [0, 10, 6, 10], [-16, -9, 0, 9], [30, 0, 0, 0], [24, -2, 0, 2], [12, -9, 0, 9], [0, -1, -54, -1], [0, 5, -20, 5], [-22, -10, 0, 10], [-16, -3, 0, 3], [0, 10, 32, 10], [0, 15, -10, 15], [34, 12, 0, -12], [0, 11, -14, 11], [12, -4, 0, 4], [0, -3, -18, -3], [0, -8, 8, -8], [26, 8, 0, -8], [0, -2, -22, -2], [28, 1, 0, -1], [0, -11, -2, -11], [0, 2, 30, 2], [16, 2, 0, -2], [0, 3, 18, 3], [-22, -18, 0, 18], [0, -1, 2, -1], [-40, 5, 0, -5], [-14, -2, 0, 2], [0, -4, 6, -4], [-36, -6, 0, 6], [30, 22, 0, -22], [28, 14, 0, -14], [-22, -4, 0, 4], [0, 13, 26, 13], [0, 6, -28, 6], [0, 5, -28, 5], [0, 14, -6, 14], [0, -8, -10, -8], [-18, 8, 0, -8], [0, 4, 38, 4], [-8, -14, 0, 14], [20, 23, 0, -23], [0, 9, 10, 9], [6, 12, 0, -12], [0, -6, -18, -6], [-32, 1, 0, -1], [0, -19, -34, -19], [-22, 10, 0, -10], [-4, 6, 0, -6], [26, -12, 0, 12], [12, -1, 0, 1], [0, 9, -4, 9], [0, 0, 42, 0], [-8, -5, 0, 5], [0, 7, 30, 7], [-14, -6, 0, 6], [-48, 1, 0, -1], [0, -11, -22, -11], [-14, 2, 0, -2], [0, -14, -6, -14], [0, 19, 22, 19], [24, 1, 0, -1], [-2, 6, 0, -6], [24, 4, 0, -4], [0, -10, -14, -10], [0, -11, -46, -11], [-20, 5, 0, -5], [0, 2, -36, 2], [0, -15, -48, -15], [-18, 4, 0, -4], [0, -4, 6, -4], [0, 6, 30, 6], [-32, 3, 0, -3], [-24, 0, 0, 0], [-26, 0, 0, 0], [0, 6, -2, 6], [0, -4, -28, -4], [-2, 6, 0, -6], [0, 12, 26, 12], [-38, -14, 0, 14], [0, 13, 10, 13], [0, -14, -32, -14], [0, -18, -26, -18], [28, -1, 0, 1], [-42, 4, 0, -4], [0, 11, 38, 11], [8, 16, 0, -16], [0, -16, -18, -16], [-36, 4, 0, -4], [-16, 1, 0, -1], [0, 13, 12, 13], [0, 19, 10, 19], [0, -10, 16, -10], [0, -9, 10, -9], [34, 20, 0, -20], [-18, 12, 0, -12], [0, -14, -30, -14], [32, 12, 0, -12], [52, 12, 0, -12], [52, 5, 0, -5], [0, -3, -60, -3], [0, -18, -42, -18], [-38, 0, 0, 0], [0, 7, 30, 7], [-32, -4, 0, 4], [0, -2, -34, -2], [4, 12, 0, -12], [0, -3, -48, -3], [-38, -2, 0, 2], [-52, -17, 0, 17], [0, -8, 0, -8], [-26, -6, 0, 6], [14, 8, 0, -8], [0, -16, -10, -16], [-36, 10, 0, -10], [54, 2, 0, -2], [0, -15, -18, -15], [0, 8, -14, 8], [38, 30, 0, -30], [0, 0, 78, 0], [44, 13, 0, -13], [-14, -16, 0, 16], [28, 19, 0, -19], [0, 23, 34, 23], [0, 1, 40, 1], [0, 14, 18, 14], [0, -8, -72, -8], [0, -9, -14, -9], [0, -8, 42, -8], [22, -10, 0, 10], [0, 5, 70, 5], [10, -4, 0, 4], [0, -31, -30, -31], [-14, 0, 0, 0], [0, 6, -58, 6], [36, 3, 0, -3], [26, -12, 0, 12], [2, 12, 0, -12], [20, 24, 0, -24], [-74, -8, 0, 8], [0, -9, -18, -9], [10, 0, 0, 0], [-34, -18, 0, 18], [0, 7, -6, 7], [20, 30, 0, -30], [62, 0, 0, 0], [0, -18, 10, -18], [0, -27, -38, -27], [0, 8, -52, 8], [0, 4, 6, 4], [0, 23, 0, -23], [0, 15, -10, 15], [-12, 8, 0, -8], [-28, -9, 0, 9], [0, -12, 10, -12], [0, -5, -26, -5], [0, -16, -46, -16], [-48, 4, 0, -4], [0, 11, -18, 11], [30, -4, 0, 4], [0, 4, 54, 4], [0, 33, 22, 33]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1920_h_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1920_2_h_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_1920_2_h_e(:prec:=4)
    chi := MakeCharacter_1920_h();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(1999) - 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_1920_2_h_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_1920_2_h_e( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1920_h();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<7,R![4, 0, 1]>,<11,R![-16, -4, 1]>,<13,R![-4, 2, 1]>],Snew);
    return Vf;
end function;