
// Make newform 420.2.bh.b in Magma, downloaded from the LMFDB on 17 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_420_bh();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_420_bh_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_420_2_bh_b();".
// 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_420_2_bh_b();".
// 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 := [243, -162, 54, -36, 39, -36, 13, -4, 2, -2, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0, 0, 0, 0, 0], [18, -21, 18, -4, 4, -2, 2, -1, 0, 0], [135, -171, 21, -51, 22, -18, 7, -9, -1, 1], [-486, -243, -216, 123, -30, 32, 28, 7, -4, 5], [-486, 9, 6, 9, -58, 16, 4, -1, 2, 3], [216, -63, 48, -15, 22, -20, 6, -1, 0, -1], [-729, 0, -153, 114, -108, 50, -23, 16, -7, 8], [-162, 54, -36, 39, -36, 13, -4, 2, -2, 1], [1701, 243, -297, 231, 186, -94, -35, 25, 5, -13]];
    Rf_basisdens := [1, 1, 18, 216, 648, 216, 72, 648, 81, 648];
    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_420_bh();"
function MakeCharacter_420_bh()
    N := 420;
    order := 6;
    char_gens := [211, 281, 337, 241];
    v := [6, 3, 6, 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_420_bh_Hecke();"
function MakeCharacter_420_bh_Hecke(Kf)
    N := 420;
    order := 6;
    char_gens := [211, 281, 337, 241];
    char_values := [[1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [-1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [1, 0, 0, 0, 0, 0, 0, 1, 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+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, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 1, 0, 0, 0], [1, 0, 0, 0, 0, 0, 0, 1, 0, 0], [-1, 0, 1, 1, -1, 1, 0, -1, 0, 1], [1, -1, 0, -1, 0, 0, 1, 1, 1, 0], [1, 0, 1, 0, -2, -1, 1, 2, 1, 0], [0, -2, -1, 0, 1, 1, 1, 1, -2, 0], [0, 0, 0, 0, 0, 0, 1, 0, -1, 0], [-3, 0, 2, 0, -1, 0, 0, 1, 0, 2], [2, -2, -1, -2, 2, -1, 1, 4, -1, -2], [1, 2, 1, 1, 1, 0, -2, 0, -2, 0], [0, -1, 0, 2, 0, -1, 1, -1, 1, 1], [2, -2, -1, 0, 0, -1, -1, 0, 3, 0], [-3, 0, -2, -1, 0, 0, 0, 0, 0, 1], [-2, -2, 0, -4, 0, -2, 0, 0, 0, -2], [2, 0, 2, -2, 2, 2, 2, 2, 0, 0], [-1, -1, 4, 1, -4, 2, -1, -1, -1, 2], [3, 0, 0, 0, 0, 0, -1, -3, 1, 0], [0, 1, -1, 0, 1, 3, -4, -3, 1, 0], [1, 0, 0, -3, 0, 1, -1, 2, -1, -3], [-1, 4, -2, 1, -2, 3, -1, -1, -4, 0], [0, 0, 0, -4, 4, 0, 1, 2, 1, -2], [-1, 4, 5, 0, 0, -4, -4, 0, 0, 0], [-6, -1, 0, 0, 3, -1, 0, -6, 0, 0], [0, -3, -1, -1, 2, -1, 1, 0, -2, -1], [2, -5, -3, -2, 3, 2, 3, 0, -5, -4], [-4, 2, 0, 0, 0, -2, 0, 1, 0, 3], [-1, -2, 2, 0, -1, 2, -2, 3, 2, -2], [1, -1, -3, -1, 3, 3, -2, 1, -1, -2], [0, 2, 2, 4, -4, 2, -2, 0, 0, 4], [-1, 4, 3, 0, 0, -5, -5, 0, 1, 0], [-6, 0, 0, 4, -2, 0, -4, -8, -4, 2], [6, -2, -1, 0, -1, 3, 5, 3, 2, 0], [2, -5, -2, -2, 4, -5, 5, 4, 0, -2], [-2, 2, -6, 0, 3, -2, -4, 1, 4, 1], [-1, -1, 5, 1, -5, 3, -2, 2, -1, 2], [8, 2, 0, -4, 0, 2, 0, 6, -2, 0], [4, 2, 0, 0, -6, 2, 0, 4, 0, 0], [5, 4, -3, -2, 0, -4, -4, 0, 0, 2], [-8, 0, 0, 0, 4, 0, 2, -8, 2, 0], [10, 0, 0, 2, 0, 2, 2, 4, 0, 0], [-5, 5, 1, 5, -2, -1, 1, -10, 6, 5], [-6, 0, -4, 0, 2, 0, 4, 6, -4, 0], [-3, 2, 4, 3, -4, 3, -5, -9, 2, 6], [3, -5, -1, 0, 2, -8, 8, 6, 3, 0], [1, -1, 1, 1, 1, 3, 4, 0, 1, 0], [6, -5, -3, 1, 0, 7, 7, 0, -2, -1], [0, 0, 2, 8, -4, 0, 0, 0, 0, 8], [-2, 0, -5, 2, 5, 3, -3, -7, 0, 4], [-3, -2, 6, 0, -3, 2, 0, 2, 0, 1], [0, 2, -8, 0, 4, -2, 0, 4, 0, -4], [0, 0, 4, 6, -8, -2, 2, 0, 2, 6], [5, 5, -1, 1, -1, -1, -6, 2, -5, 0], [7, -6, 0, -1, 0, -1, -1, 0, 7, 1], [-7, 5, 0, 8, -11, 5, -1, -11, -1, 4], [8, -2, -4, 4, -4, 1, 3, 2, 2, 0], [5, -2, -5, -5, 5, -2, 4, 11, -2, -10], [-5, 0, 2, 0, -1, 0, 3, 0, -3, 5], [1, 0, -4, -1, 4, -1, 1, 9, 0, -2], [4, 6, 0, 4, 0, 6, -6, 8, 0, 4], [-7, -2, -2, 3, -2, -5, -3, -5, 2, 0], [2, 2, -8, 2, 0, 0, 0, 0, -2, -2], [-5, -3, 1, 0, -2, 1, -1, -10, -4, 0], [-5, 7, 6, 5, -6, -4, -3, -3, 7, 10], [0, 1, 4, 0, -2, -1, -5, -5, 5, 5], [-5, 3, 6, 0, -3, -3, -1, 11, 1, -6], [7, -2, 0, -2, -3, -2, -6, 8, -6, -1], [-3, 0, 1, -4, 0, -5, -5, 0, 5, 4], [4, 0, 0, 0, 0, -7, -7, 2, 0, 0], [-3, -4, -3, -7, 6, 0, 0, -6, -4, -7], [2, 0, -3, -2, 3, 3, -3, -9, 0, -4], [-8, -3, 4, 0, -2, 3, 4, 5, -4, 3], [-8, -1, -1, 2, -1, 3, 4, -5, 1, 0], [-3, 1, 0, 4, 3, 1, -4, -5, -4, 2], [0, -4, -5, -1, 0, -2, -2, 0, 6, 1], [-6, -3, 0, 0, -6, -3, -1, -6, -1, 0], [-1, -5, 2, -3, 2, -2, 3, 1, 5, 0], [-6, -5, -4, 0, 2, 5, -5, 3, 5, 3], [-2, 12, 6, 0, -3, -12, -4, -1, 4, 3], [-2, 0, 2, 0, 2, 0, 0, -1, 0, 0], [14, 6, 2, 0, 0, -4, -4, 0, -2, 0], [-1, -1, -3, -3, 0, 7, 7, 0, -6, 3], [10, 4, 4, -2, 4, 0, -4, 6, -4, 0], [1, 2, -1, 0, 2, 11, -11, 2, -9, 0], [-1, -2, -10, 0, 5, 2, 5, 2, -5, -1], [-8, -5, 0, 0, 0, 5, -1, 6, 1, 2], [1, 2, -3, -7, 6, 0, 0, 2, 2, -7], [1, 3, 0, 0, -1, 3, 8, 1, 8, 0], [-13, -8, 6, 1, 0, 5, 5, 0, 3, -1], [11, -3, 1, -2, 0, -1, -1, 0, 4, 2], [-8, -5, 0, -4, 6, -5, 1, -6, 1, -2], [0, 4, 0, 0, 0, 0, -4, 6, 4, 0], [-2, 9, 7, 2, -7, -10, 1, 3, 9, 4], [4, 6, 2, 0, -4, 12, -12, 8, -6, 0], [-5, 2, 0, -2, 3, 2, -2, -4, -2, -1], [16, -7, -4, 4, 0, 8, 8, 0, -1, -4], [-4, 6, 0, 2, -5, 6, 4, -5, 4, 1], [-2, 0, 6, 2, -6, -4, 4, 18, 0, 4], [1, 3, 2, 0, -1, -3, 0, 5, 0, -6], [-13, -2, 0, 4, -4, -2, 0, -15, 0, 2], [8, 5, -12, 6, 0, -4, -4, 0, -1, -6], [20, -8, 2, -4, 2, -2, 6, 12, 8, 0], [0, 6, 0, 0, 0, -1, -5, -6, 6, 0], [-4, -9, 0, 0, 0, 9, -2, 1, 2, 3], [0, -9, -8, 0, 8, -5, 14, 16, -9, 0], [10, -5, 3, -4, 3, -2, 3, 7, 5, 0], [5, 1, -1, 0, 0, 6, 6, 0, -7, 0], [-9, -3, 0, -4, 5, -3, 3, -7, 3, -2], [4, 2, 0, -4, 0, -6, -8, 4, -2, 0], [-8, 13, 6, 8, -12, 9, -9, -16, 4, 8], [1, 6, 6, 0, -3, -6, -5, -7, 5, 6], [1, -5, 3, -1, -3, -3, 8, -16, -5, -2], [6, -2, 2, 8, -4, -4, 4, 12, 2, 8], [1, -8, -1, 1, -1, 2, 10, 0, 8, 0], [-10, -4, 6, 0, 0, 12, 12, 0, -8, 0], [0, 1, 3, -8, 3, -10, -11, 4, -1, 0], [7, 2, 3, 2, -6, 1, -1, 14, 1, 2], [6, 6, -1, -6, 1, -4, -2, 31, 6, -12], [1, 1, 2, 0, -1, -1, -3, -3, 3, 2], [6, -2, 2, -2, -4, -12, 12, 12, 10, -2], [21, -1, -7, 11, -7, 7, 8, 5, 1, 0], [-7, -4, -5, 0, 0, -5, -5, 0, 9, 0], [9, -7, 0, -12, 9, -7, 11, 15, 11, -6], [2, -8, 7, -12, 7, -10, -2, 7, 8, 0], [-1, -4, 18, 0, -9, 4, -2, -10, 2, 11], [-2, -2, -5, -2, 10, 9, -9, -4, -11, -2], [17, 2, 0, 8, -10, 2, 5, 13, 5, 4], [-10, -6, 0, -12, 2, -6, 6, -4, 6, -6], [-9, -2, -4, -3, 8, 2, -2, -18, -4, -3], [-7, -7, -6, 0, 3, 7, -2, 5, 2, 2], [-6, -1, 0, 6, 0, 1, 0, -4, -1, 12], [-7, 6, 3, 10, -6, 4, -4, -14, 2, 10], [-19, 0, 0, -6, 9, 0, -6, -16, -6, -3], [10, 4, 4, -2, 0, -8, -8, 0, 4, 2], [14, 3, 0, 6, -10, 3, -6, 11, -6, 3], [-8, 5, 0, 6, 0, 13, -13, -16, -8, 6], [-2, 0, -3, 2, 3, 3, -3, 21, 0, 4], [10, 0, 0, 2, 0, -3, -3, 4, 0, 0], [-7, 11, 7, 2, 0, -6, -6, 0, -5, -2], [31, -4, -5, 9, -5, -4, 0, 11, 4, 0], [-6, 3, -11, -5, 22, 3, -3, -12, 0, -5], [-2, 1, 4, 0, -2, -1, 4, 3, -4, -1], [3, 3, -7, -3, 7, -2, -1, -12, 3, -6], [-8, -5, 2, -6, -4, -10, 10, -16, 5, -6], [-4, -3, 4, -8, 4, -13, -10, 2, 3, 0], [11, 10, -6, 7, 0, 3, 3, 0, -13, -7], [17, -1, -2, -11, 4, -8, 8, 34, 7, -11], [0, -6, 5, 0, -5, 9, -3, -11, -6, 0], [-3, 2, -6, 0, 3, -2, -5, 2, 5, 1], [6, -3, 8, 0, -4, 3, 5, 2, -5, -8], [-2, -12, 0, -20, 4, -12, 6, 8, 6, -10], [5, -8, 1, 5, 0, 2, 2, 0, 6, -5], [-33, -3, 8, -3, 0, 6, 6, 0, -3, 3], [-17, 6, 0, 8, 3, 6, -2, -21, -2, 4], [5, 6, -14, -5, 14, -10, 4, 3, 6, -10], [-9, 6, 2, 3, -4, 11, -11, -18, -5, 3], [-17, 10, 0, 18, -7, 10, -12, -26, -12, 9], [14, -1, 0, -8, -3, -1, -6, 18, -6, -4], [-5, -5, 2, 5, -4, 6, -6, -10, -11, 5], [3, 3, -8, -3, 8, 4, -7, -25, 3, -6], [5, 4, -18, 0, 9, -4, 2, 7, -2, -12], [-2, 8, 8, 6, -16, -2, 2, -4, 10, 6], [-9, -2, 2, 1, 0, -10, -10, 0, 12, -1], [6, -2, 0, 8, -10, -2, 8, 2, 8, 4], [-4, 4, -5, 6, -5, -1, -5, -5, -4, 0], [0, 6, 1, 0, -1, -14, 8, -7, 6, 0], [6, -1, -2, -6, 2, 5, -4, 12, -1, -12], [9, 2, 0, 15, 0, 9, 7, -3, -2, 0]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_420_bh_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_420_2_bh_b();".
// 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_420_2_bh_b(:prec:=10)
    chi := MakeCharacter_420_bh();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(997) - 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_420_2_bh_b();".
// 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_420_2_bh_b( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_420_bh();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<11,R![1728, -7488, 14128, -14352, 8156, -2280, 84, 96, -4, -6, 1]>],Snew);
    return Vf;
end function;