
// Make newform 1680.2.bg.q in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1680_bg();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_1680_bg_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_1680_2_bg_q();".
// 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_1680_2_bg_q();".
// 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 := [49, 0, 7, 0, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]];
    Rf_basisdens := [1, 1, 7, 7];
    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_1680_bg();"
function MakeCharacter_1680_bg()
    N := 1680;
    order := 3;
    char_gens := [1471, 421, 1121, 337, 241];
    v := [3, 3, 3, 3, 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;

// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_1680_bg_Hecke();"
function MakeCharacter_1680_bg_Hecke(Kf)
    N := 1680;
    order := 3;
    char_gens := [1471, 421, 1121, 337, 241];
    char_values := [[1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0], [0, 0, 1, 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+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, 0, 0], [1, 0, 1, 0], [0, 0, 1, 0], [0, 1, 0, 1], [1, 1, 1, 0], [0, 0, 0, -1], [-1, -1, -1, 0], [0, 2, -3, 2], [0, 1, 1, 1], [5, 0, 0, 1], [1, 2, 1, 0], [0, -1, -2, -1], [-3, 0, 0, 3], [-2, 0, 0, 3], [0, 0, -6, 0], [2, 2, 2, 0], [3, -3, 3, 0], [0, 0, 8, 0], [-2, -1, -2, 0], [-11, 0, 0, -1], [0, 5, 0, 0], [0, 2, 3, 2], [3, 0, 0, 3], [0, 5, -1, 5], [8, 0, 0, 0], [-3, -3, -3, 0], [0, -1, -12, -1], [0, -3, 9, -3], [13, 0, 13, 0], [6, 0, 0, 0], [10, 0, 0, -3], [0, 2, -16, 2], [7, -5, 7, 0], [-5, 0, 0, 0], [0, 4, 4, 4], [6, 4, 6, 0], [-4, -2, -4, 0], [0, 0, 16, 0], [-17, 0, 0, -1], [0, -6, -6, -6], [-10, -4, -10, 0], [1, 0, 0, -2], [0, 8, 2, 8], [16, 3, 16, 0], [3, 0, 0, -3], [-2, 8, -2, 0], [2, 0, 0, -4], [-2, 0, 0, -6], [17, -1, 17, 0], [0, 0, -7, 0], [0, -2, 16, -2], [-6, 0, 0, 0], [18, 2, 18, 0], [3, 0, 0, 3], [0, -7, -13, -7], [-2, 10, -2, 0], [-12, 6, -12, 0], [0, -4, -18, -4], [18, -1, 18, 0], [24, 0, 0, 0], [-12, 1, -12, 0], [0, 0, 0, 0], [-20, 0, 0, -3], [11, -1, 11, 0], [0, 5, -8, 5], [0, -7, 5, -7], [0, -8, -1, -8], [-20, 0, 0, -5], [-8, -8, -8, 0], [-10, 0, 0, 0], [7, -11, 7, 0], [0, -9, -3, -9], [-6, -5, -6, 0], [0, 3, 8, 3], [21, 0, 0, -2], [0, -2, 22, -2], [19, 7, 19, 0], [0, -1, -14, -1], [0, 2, 14, 2], [15, 8, 15, 0], [-16, 0, 0, -2], [-9, 0, 0, -4], [24, -6, 24, 0], [6, 0, 0, -1], [0, 2, 0, 2], [0, 6, 6, 6], [-2, 0, 0, -4], [0, 1, -12, 1], [-17, 0, 0, -1], [8, 0, 0, -7], [0, -12, 6, -12], [4, 4, 4, 0], [0, 1, 0, 0], [-18, 0, 0, 6], [0, 10, -1, 10], [4, 0, 0, -10], [0, 6, -12, 6], [18, 6, 18, 0], [0, 5, -18, 5], [0, -12, 5, -12], [38, 0, 0, 2], [18, 0, 18, 0], [-26, 4, -26, 0], [0, -5, -17, -5], [39, -2, 39, 0], [24, -7, 24, 0], [-9, 0, 0, -3], [0, -3, -33, -3], [18, 6, 18, 0], [-27, 0, 0, -4], [0, 5, 30, 5], [20, -8, 20, 0], [4, 0, 0, 2], [-19, 0, -19, 0], [4, 0, 0, 12], [-17, -11, -17, 0], [-2, 0, 0, 9], [15, -3, 15, 0], [0, 1, 31, 1], [24, 0, 0, 0], [25, -6, 25, 0], [-8, 0, 0, 1], [0, -1, -25, -1], [-3, -3, -3, 0], [0, 4, -13, 4], [27, 0, 0, 3], [0, 4, -12, 4], [0, 2, 20, 2], [10, 0, 0, 9], [0, -5, -6, -5], [29, 0, 29, 0], [21, 0, 0, -3], [0, 8, -3, 8], [-30, 0, 0, 8], [0, 11, 17, 11], [-9, 0, 0, 2], [7, 13, 7, 0], [-10, -6, -10, 0], [-3, 0, 0, 3], [2, 8, 2, 0], [-12, 0, 0, -2], [0, 17, -7, 17], [-8, -10, -8, 0], [4, 0, 0, -10], [-25, -2, -25, 0], [-19, 0, 0, 1], [30, 0, 0, 5], [11, -1, 11, 0], [0, -10, 0, -10], [0, -10, 8, -10], [0, 0, 14, 0], [-20, 0, 0, 8], [-2, 0, 0, 9], [0, -1, 17, -1], [-18, 1, -18, 0], [-13, 0, 0, 7], [0, -4, -21, -4], [0, -7, 17, -7], [-6, 0, 0, 17], [3, -3, 3, 0], [0, 1, 43, 1], [-26, 0, 0, -10], [-6, 0, 0, 13], [0, -8, -32, -8], [33, 3, 33, 0], [-15, -15, -15, 0], [39, -2, 39, 0], [-30, 5, -30, 0], [-9, 0, 0, 14], [0, 15, -21, 15], [-10, 14, -10, 0], [-6, 0, 0, 14], [0, 13, -5, 13], [12, 11, 12, 0], [11, -12, 11, 0], [12, 0, 0, -12], [-3, 0, 0, -14], [0, 6, 0, 0], [20, 0, 0, 8], [0, -12, -13, -12], [0, 1, -22, 1], [9, 0, 0, -3], [12, 0, 0, -1], [0, -10, 14, -10], [18, -12, 18, 0], [-42, -6, -42, 0], [16, -18, 16, 0], [10, 5, 10, 0], [0, 12, -25, 12], [15, 3, 15, 0], [0, 3, 14, 3], [29, 0, 0, 1], [0, -8, -16, -8], [0, 0, 60, 0], [-13, 11, -13, 0], [39, 3, 39, 0], [1, -24, 1, 0], [0, -12, 32, -12], [-40, 0, 0, -2], [0, -9, 15, -9], [0, -18, 0, 0], [21, 0, 0, -2], [0, 6, -16, 6], [0, -16, 0, 0], [3, 0, 0, -15], [-16, -10, -16, 0], [0, -4, -36, -4], [0, 0, 6, 0], [26, 0, 0, -2], [-4, 18, -4, 0], [0, 3, -28, 3], [51, 0, 0, 3], [-54, 0, 0, -2], [0, 4, -44, 4], [7, 1, 7, 0], [0, 4, -27, 4], [0, -8, 0, 0], [-24, 0, -24, 0], [0, -10, 2, -10], [-6, 0, 0, -12], [0, -6, 29, -6], [5, 0, 0, 2], [0, -15, -27, -15], [0, -16, 24, -16], [-16, 0, 0, -14], [-8, 0, 0, 4], [0, 12, 0, 12], [-12, -6, -12, 0], [0, 11, -18, 11], [0, -1, 35, -1], [-18, -13, -18, 0], [-12, -8, -12, 0], [-27, 0, 0, -8], [-35, 13, -35, 0], [14, 0, 0, -1], [7, 1, 7, 0], [0, 14, -5, 14], [0, 9, 39, 9], [-20, 0, 0, -4], [-1, 0, 0, 13], [-27, -9, -27, 0], [0, -10, -3, -10], [34, -7, 34, 0], [0, -18, 2, -18], [54, 0, 0, 6], [0, -18, -18, -18], [44, 0, 0, -1], [5, -19, 5, 0], [44, -6, 44, 0], [20, 0, 0, -20], [24, 0, 0, -1], [0, -8, 52, -8], [22, 4, 22, 0], [-53, 0, 0, -8], [-14, 10, -14, 0], [0, -5, -23, -5], [3, 26, 3, 0], [54, 7, 54, 0], [25, 0, 0, -19], [0, 12, 14, 12], [-30, 13, -30, 0], [-6, 0, 0, -18], [-53, 0, -53, 0], [50, 0, 0, 3], [24, 18, 24, 0], [0, -4, 21, -4], [-13, 0, 0, -11], [-6, 0, 0, 12], [-56, 0, 0, 6], [-33, -3, -33, 0], [0, -20, -15, -20], [24, 10, 24, 0], [28, 9, 28, 0], [0, -6, -35, -6], [12, 0, 0, -22], [0, 2, -30, 2], [0, -5, -11, -5], [25, 12, 25, 0], [0, -2, 27, -2], [0, -20, -8, -20], [-10, 14, -10, 0], [-49, 0, -49, 0], [-6, 0, 0, 12], [37, 0, 0, -8], [0, 6, -26, 6], [0, 1, 37, 1], [-2, -9, -2, 0], [59, 0, 0, 7], [17, -12, 17, 0], [-11, 0, 0, -1], [10, 10, 10, 0], [26, 2, 26, 0], [0, 9, 39, 9], [-29, 0, 0, -1], [16, 0, 0, 7], [6, -24, 6, 0], [0, 16, 35, 16], [-1, 0, 0, 1], [0, 7, 43, 7], [-14, 0, 0, 9], [0, -20, -30, -20], [0, -22, 8, -22], [4, 14, 4, 0]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1680_bg_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1680_2_bg_q();".
// 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_1680_2_bg_q(:prec:=4)
    chi := MakeCharacter_1680_bg();
    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_1680_2_bg_q();".
// 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_1680_2_bg_q( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1680_bg();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<11,R![36, 12, 10, -2, 1]>,<13,R![-7, 0, 1]>,<17,R![36, -12, 10, 2, 1]>],Snew);
    return Vf;
end function;