
// Make newform 882.2.f.n in Magma, downloaded from the LMFDB on 17 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_882_f();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_882_f_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_f_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_f_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 := [3, -12, 19, -15, 10, -3, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0], [6, 0, 1, 5, -1, 1], [0, -3, 2, -5, 1, -1], [6, -21, 19, -16, 5, -2], [-9, 33, -22, 19, -5, 2]];
    Rf_basisdens := [1, 1, 3, 3, 3, 3];
    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_f();"
function MakeCharacter_882_f()
    N := 882;
    order := 3;
    char_gens := [785, 199];
    v := [2, 3];
    // 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_f_Hecke();"
function MakeCharacter_882_f_Hecke(Kf)
    N := 882;
    order := 3;
    char_gens := [785, 199];
    char_values := [[0, 0, 0, 0, 1, 0], [1, 0, 0, 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+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 := [[1, 0, 0, 0, 1, 0], [-1, 0, 0, 0, 0, 1], [1, -1, 0, 1, -1, -1], [0, 0, 0, 0, 0, 0], [0, 0, 1, 0, 0, -1], [1, -3, 0, 1, -4, 1], [2, 0, 2, 2, 0, 0], [2, 0, 3, 3, 0, 0], [0, -1, 0, 0, 2, 1], [0, 3, 5, 3, 0, -5], [1, 0, 0, 1, -7, -2], [-1, 0, 0, 0, 0, 0], [-2, 1, 0, -2, 1, 3], [-2, 3, 0, 3, -2, 0], [-3, 3, 0, 3, -3, 0], [-4, -1, 0, 2, -1, 0], [2, -3, 0, 2, 3, -1], [3, -1, 1, -1, 3, -1], [-4, 3, 0, -4, 2, 5], [6, -2, 5, 9, -2, 0], [-4, -4, -5, 3, -4, 0], [0, -4, -5, -4, 0, 5], [1, -2, 1, -2, 1, -1], [1, 1, -3, -5, 1, 0], [8, -2, -4, -2, 8, 4], [-10, -4, -1, -4, -10, 1], [0, -3, 0, 0, -1, 3], [-8, 1, 6, 4, 1, 0], [2, -1, -2, 0, -1, 0], [3, -2, 0, 3, 10, -4], [8, -5, -10, 0, -5, 0], [-2, 2, 0, -2, 2, 2], [8, 5, 8, 5, 8, -8], [-4, 3, 0, -4, -1, 5], [8, -13, 0, 8, -7, -3], [2, 1, -1, 1, 2, 1], [3, 0, 0, 3, -4, -6], [-4, -3, -9, -3, -3, 0], [0, 1, 0, 0, -5, -1], [-2, -11, -10, -11, -2, 10], [-1, 2, 9, 5, 2, 0], [-4, 4, 5, -3, 4, 0], [9, 6, 9, 6, 9, -9], [3, -3, 0, 3, 2, -3], [-15, 4, -4, -12, 4, 0], [-13, 0, -3, -3, 0, 0], [-6, 12, 0, -6, 5, 0], [7, -6, 0, -6, 7, 0], [13, 7, 6, 7, 13, -6], [-4, 6, 0, -4, 2, 2], [4, 2, 5, 1, 2, 0], [-2, -2, 0, -2, 7, 6], [13, 0, 0, 0, 13, 0], [0, -3, 3, 9, -3, 0], [-1, -1, 0, -1, 5, 3], [-2, -8, -9, -8, -2, 9], [8, -8, -14, 2, -8, 0], [5, -8, -7, 9, -8, 0], [-14, 0, -9, 0, -14, 9], [-5, 1, -8, 1, -5, 8], [2, -3, 0, 2, -22, -1], [10, -14, 0, 10, -5, -6], [-4, -4, 1, 9, -4, 0], [-1, 3, 0, -1, 0, -1], [-4, -2, -4, -2, -4, 4], [-3, 3, -6, 3, -3, 6], [16, -3, 0, -3, 16, 0], [-2, 0, 0, -2, 17, 4], [3, -9, 0, 3, 3, 3], [11, 1, -7, 1, 11, 7], [-2, 1, -3, 1, -2, 3], [-14, 9, 4, -14, 9, 0], [10, 6, 3, 6, 10, -3], [5, -6, 0, 5, -1, -4], [14, -1, 7, 9, -1, 0], [-3, 8, 0, -3, -7, -2], [23, 2, -1, 2, 23, 1], [20, -8, -10, 6, -8, 0], [-4, 17, 0, -4, 5, -9], [-3, 3, 0, -3, -1, 3], [-2, 10, 0, -2, -8, -6], [0, 2, 4, 2, 0, -4], [-19, 8, -6, -22, 8, 0], [-7, 3, -3, -9, 3, 0], [9, 14, 13, 14, 9, -13], [-4, -10, -5, -10, -4, 5], [15, -7, -11, 3, -7, 0], [26, 1, -1, 1, 26, 1], [0, 3, 2, 3, 0, -2], [8, -21, 0, 8, -16, 5], [-2, -9, -2, 16, -9, 0], [-3, -3, -11, -3, -3, 11], [-7, 0, -15, -15, 0, 0], [-2, 7, 0, -2, 16, -3], [-13, 18, 0, -13, 14, 8], [-33, -3, -3, 3, -3, 0], [-4, 8, 0, -4, 5, 0], [2, -1, -12, -10, -1, 0], [-7, 9, 21, 3, 9, 0], [-19, 4, 11, 3, 4, 0], [12, -4, -11, -4, 12, 11], [-10, -8, -5, 11, -8, 0], [-5, -6, 0, -5, -15, 16], [-21, -6, -6, -6, -21, 6], [7, -21, 0, 7, -10, 7], [-25, -1, 7, 9, -1, 0], [-8, -2, 7, -2, -8, -7], [1, -8, 6, 22, -8, 0], [-3, 3, 0, -3, -12, 3], [-17, -3, -6, -3, -17, 6], [-5, 6, 0, -5, -4, 4], [-4, -2, 5, 9, -2, 0], [5, 10, 0, 5, -20, -20], [17, -11, -10, -11, 17, 10], [2, 15, 12, -18, 15, 0], [-24, 3, 4, 3, -24, -4], [6, -21, 0, 6, -19, 9], [-7, 5, 0, -10, 5, 0], [-7, 20, 0, -7, 26, -6], [-2, -5, -8, -5, -2, 8], [5, -21, 0, 5, -13, 11], [7, 12, 24, 12, 7, -24], [0, -3, -3, -3, 0, 3], [14, -4, 3, 11, -4, 0], [-8, -9, -9, -9, -8, 9], [-3, -4, -23, -15, -4, 0], [-17, -9, 0, -9, -17, 0], [-38, 7, -3, -17, 7, 0], [17, 7, 8, 7, 17, -8], [13, -18, 0, 13, -19, -8], [11, 1, 17, 15, 1, 0], [-8, 4, 0, -8, 13, 12], [1, -3, 0, 1, 5, 1], [-7, 1, 5, 3, 1, 0], [-3, 5, 0, -3, 8, 1], [5, 15, 0, 5, -7, -25], [-13, -5, -11, -1, -5, 0], [-5, -6, 0, -5, -13, 16], [-11, -2, 0, -11, -2, 24], [11, -8, -11, 5, -8, 0], [-7, 2, 19, 15, 2, 0], [-31, -1, -8, -1, -31, 8], [-4, 15, 0, -4, 23, -7], [-15, 6, -3, -15, 6, 0], [11, 8, 7, -9, 8, 0], [34, 4, 1, 4, 34, -1], [-14, -9, -6, -9, -14, 6], [-5, -2, -15, -2, -5, 15], [9, -9, 0, 9, 2, -9], [1, 0, 1, 1, 0, 0], [8, -12, 0, 8, -25, -4], [-12, -9, -12, 6, -9, 0], [8, -12, -18, 6, -12, 0], [11, 2, 0, 11, -10, -24], [-3, -1, -17, -1, -3, 17], [29, 2, 0, 2, 29, 0], [26, -13, -2, 24, -13, 0], [42, 3, 0, 3, 42, 0], [-4, -3, -3, 3, -3, 0], [2, 0, 0, 2, 6, -4], [1, -8, -4, -8, 1, 4], [6, -2, 14, 18, -2, 0], [-3, 9, 0, -3, -34, -3], [1, 4, -6, -14, 4, 0], [9, -3, 0, 9, -27, -15], [22, -11, 6, -11, 22, -6], [-25, 3, 0, -6, 3, 0], [4, 0, 3, 0, 4, -3]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_882_f_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_882_2_f_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_f_n(:prec:=6)
    chi := MakeCharacter_882_f();
    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_f_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_f_n( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_882_f();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![9, 18, 33, 12, 7, -1, 1]>,<11,R![9, -18, 33, -12, 7, 1, 1]>,<13,R![4761, 69, 553, -146, 63, -8, 1]>],Snew);
    return Vf;
end function;