
// Make newform 882.2.h.n in Magma, downloaded from the LMFDB on 06 September 2025.
// To make the character of type GrpDrchElt, type "MakeCharacter_882_h();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_882_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_882_2_h_n();".
// 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_882_2_h_n();".
// 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 := [9, -3, -2, -1, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [0, 1, 0, 0], [-3, -2, 2, 1], [3, 2, 0, -1]];
    Rf_basisdens := [1, 1, 6, 2];
    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_882_h();"
function MakeCharacter_882_h()
    N := 882;
    order := 3;
    char_gens := [785, 199];
    v := [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_882_h_Hecke();"
function MakeCharacter_882_h_Hecke( : Kf := false)
    N := 882;
    order := 3;
    char_gens := [785, 199];
    char_values := [[-1, 0, 1, 0], [0, 0, -1, 0]];
    assert UnitGenerators(DirichletGroup(N)) eq char_gens;
    values := ConvertToHeckeField(char_values : pass_field := ISA(Type(Kf), Fld), 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 := [[1, 0, -1, 0], [0, 0, 1, 1], [-2, 1, 1, 1], [0, 0, 0, 0], [1, 1, 1, 1], [2, 0, -2, 0], [-2, 1, 1, -2], [0, 0, 5, 0], [-4, -1, -1, -1], [2, -4, 2, 2], [0, 0, 2, 0], [0, 0, -2, 0], [8, -1, -7, 2], [3, -6, -2, 3], [0, 0, 0, 0], [2, 2, -4, -4], [-3, 6, 0, -3], [-7, 3, 4, -6], [3, -6, -8, 3], [0, 3, 3, 3], [2, 3, -5, -6], [-5, 3, 2, -6], [4, -8, 4, 4], [2, -4, 8, 2], [-3, 6, 2, -3], [-4, -1, -1, -1], [10, 0, 0, 0], [1, -2, 4, 1], [-14, 0, 14, 0], [1, 1, -2, -2], [-4, -3, -3, -3], [4, 1, 1, 1], [13, 1, 1, 1], [-7, 6, 1, -12], [8, 2, 2, 2], [2, -3, -3, -3], [3, -6, -1, 3], [6, -12, -2, 6], [8, -4, -4, 8], [-6, 0, 6, 0], [-10, 2, 8, -4], [-8, -3, -3, -3], [9, 3, -12, -6], [0, 0, 7, 0], [-6, 0, 0, 0], [-10, 0, 10, 0], [16, 0, -16, 0], [0, 0, -4, 0], [17, 2, 2, 2], [10, 3, 3, 3], [-2, 4, 7, -2], [7, -5, -2, 10], [-11, 3, 3, 3], [9, 0, 0, 0], [-5, -5, -5, -5], [10, 1, 1, 1], [-5, 1, 4, -2], [6, -12, -4, 6], [2, 6, 6, 6], [-1, 2, -13, -1], [3, -6, 17, 3], [-7, -1, 8, 2], [13, 0, 0, 0], [6, -12, -12, 6], [-10, -3, 13, 6], [6, 0, -6, 0], [-2, -6, 8, 12], [-2, 3, -1, -6], [3, -6, 0, 3], [0, 0, -22, 0], [11, -1, -1, -1], [-5, 10, -5, -5], [-2, -6, -6, -6], [-10, 0, 0, 0], [-1, 3, 3, 3], [28, -2, -2, -2], [-8, -8, -8, -8], [0, 0, -22, 0], [-7, 2, 2, 2], [-9, 18, 8, -9], [11, -7, -4, 14], [-6, 12, -14, -6], [20, -4, -16, 8], [13, -3, -3, -3], [8, 0, -8, 0], [30, 3, -33, -6], [33, 0, 0, 0], [-5, 12, -7, -24], [-5, 10, 19, -5], [13, 3, -16, -6], [11, -22, -4, 11], [-28, 2, 2, 2], [-5, -9, 14, 18], [22, 1, -23, -2], [11, -3, -3, -3], [18, -6, -6, -6], [10, -8, -8, -8], [-8, -5, 13, 10], [-3, 6, -25, -3], [6, -12, -14, 6], [-3, 6, -8, -3], [-16, -4, 20, 8], [0, 0, 3, 0], [-6, -3, 9, 6], [9, -18, -8, 9], [20, -3, -17, 6], [4, -8, 1, 4], [2, -4, 8, 2], [0, 0, -24, 0], [3, -6, 14, 3], [-8, 6, 6, 6], [16, 6, -22, -12], [-2, -5, 7, 10], [-17, 12, 12, 12], [-16, 9, 9, 9], [1, -14, -14, -14], [-4, 9, -5, -18], [-8, 4, 4, -8], [-22, 2, 2, 2], [2, -4, 14, 2], [3, -6, 17, 3], [-3, 6, 13, -3], [-6, 12, -6, -24], [14, -13, -1, 26], [-13, -3, 16, 6], [-24, 6, 6, 6], [-44, 0, 44, 0], [2, -4, -4, 2], [-6, 12, -16, -6], [34, -3, -3, -3], [-2, 3, -1, -6], [-20, 10, 10, -20], [-10, 3, 3, 3], [32, -6, -6, -6], [-26, 4, 4, 4], [-10, 0, 10, 0], [-23, -5, 28, 10], [0, 0, -4, 0], [-25, 5, 20, -10], [-10, 5, 5, -10], [-35, 3, 3, 3], [24, -6, -18, 12], [6, -12, -8, 6], [12, 0, 0, 0], [-34, 6, 28, -12], [4, -8, -8, 4], [-3, 6, -25, -3], [2, -16, -16, -16], [-41, -3, -3, -3], [-5, 10, 7, -5], [-16, 18, 18, 18], [6, -6, -6, -6], [-19, 9, 9, 9], [-2, 10, 10, 10], [-19, 3, 3, 3], [-1, 2, 41, -1], [3, -6, 37, 3], [24, 6, -30, -12], [-2, 12, 12, 12], [3, -6, 9, 3], [-24, -3, 27, 6], [21, -3, -3, -3], [-41, 3, 38, -6], [-1, 2, 5, -1], [-3, 6, -30, -3], [44, 2, 2, 2], [-8, -12, 20, 24], [-2, -3, -3, -3]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_882_h_Hecke( : Kf := Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_882_2_h_n();".
// 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_882_2_h_n(:prec:=4)
    chi := MakeCharacter_882_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(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_882_2_h_n();".
// 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_882_2_h_n( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_882_h();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![-6, 3, 1]>,<11,R![-6, -3, 1]>,<13,R![4, -2, 1]>],Snew);
    return Vf;
end function;