
// Make newform 4830.2.a.bt in Magma, downloaded from the LMFDB on 24 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_4830_a();"
// To make the coeffs of the qexp of the newform in the Hecke field type "qexpCoeffs();"
// To make the newform (type ModFrm), type "MakeNewformModFrm_4830_2_a_bt();".
// 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_4830_2_a_bt();".
// 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, 0, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0], [0, 2]];
    Rf_basisdens := [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_4830_a();"
function MakeCharacter_4830_a()
    N := 4830;
    order := 1;
    char_gens := [3221, 967, 2761, 1891];
    v := [1, 1, 1, 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;

function MakeCharacter_4830_a_Hecke(Kf)
    return MakeCharacter_4830_a();
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], [-1, 0], [-1, 0], [-1, 0], [-2, 1], [0, 1], [-2, 0], [4, 0], [-1, 0], [-4, 1], [4, 0], [-2, -2], [2, 0], [2, -1], [0, -2], [2, 0], [0, 2], [10, 0], [2, -1], [-6, -1], [2, 0], [4, 2], [4, 0], [8, -1], [4, 1], [8, -3], [0, 4], [4, -2], [10, 0], [-6, 4], [2, 3], [4, 4], [2, 4], [4, -4], [-2, -2], [4, 2], [10, 4], [-8, -2], [12, 0], [-2, -2], [16, -2], [2, 0], [8, 0], [-14, 0], [-2, 0], [20, 2], [0, -6], [6, -1], [8, -2], [2, 4], [-6, 4], [2, 3], [2, -2], [-6, -7], [-6, 0], [12, 2], [-4, -5], [-4, 0], [-4, 1], [-4, 7], [14, 3], [2, 0], [12, 4], [-6, 5], [0, -5], [-6, -2], [16, 2], [-4, -5], [-12, -4], [-6, 0], [2, -4], [0, 0], [8, -8], [-2, -2], [20, 2], [-8, -4], [18, 0], [8, 5], [-8, 1], [10, 4], [22, -1], [10, -4], [-8, -4], [4, -7], [16, 6], [20, -4], [-18, 2], [-8, 1], [0, -7], [-10, -3], [4, 4], [8, 0], [-2, -3], [-20, 0], [8, 2], [-4, -2], [0, -7], [-16, -1], [-2, -1], [10, -2], [-12, 0], [-6, 8], [-28, 4], [24, -3], [-12, -2], [2, 4], [0, -2], [-22, 0], [22, 1], [-14, 4], [-10, 3], [2, 0], [-18, 2], [20, -4], [36, 2], [-20, -1], [-10, 7], [-32, 2], [2, 2], [6, -7], [10, 0], [-34, 2], [10, 8], [-12, 8], [8, 10], [-14, -4], [-22, 0], [14, -5], [4, -10], [-14, -8], [52, 0], [-12, -6], [8, 4], [-14, 0], [-18, -10], [-2, 8], [34, 0], [-18, -5], [-6, 12], [2, 4], [-8, 10], [0, 11], [2, 11], [4, -2], [18, 0], [-36, -2], [-16, -3], [10, -12], [0, -2], [20, -6], [-20, 1], [0, 3], [0, 6], [-32, -2], [34, 3], [-28, -6], [0, -12], [2, -4], [28, -7], [-14, 8], [-24, -6], [-6, 4], [6, -11], [-6, -3], [-34, -6], [48, 0], [4, 6], [-8, 5], [18, -4], [-18, 2], [26, -9], [-2, -2], [-24, 0], [32, -3], [40, -2], [36, -7], [4, 0], [0, -1], [4, -2], [2, -8], [6, -3], [10, -11], [-44, 1], [2, -4], [24, 0], [22, 2], [-12, -3], [26, 5], [-22, -12], [-42, -1], [-34, 2], [-16, 14], [-20, -10], [-40, -3], [-8, 4], [18, 10], [22, 2], [-10, -2], [-30, 10], [-24, -10], [10, -16], [56, 2], [-28, -1], [-22, 6], [26, 9], [-2, -14], [16, 8], [0, 2], [18, -12], [12, -4], [30, -6], [24, -11], [-32, 0], [-52, 0], [26, -7], [22, -8], [34, -5], [6, -10], [28, 6], [-30, 2], [-2, 8], [-36, -2], [18, 0], [-4, 10], [4, 12], [-10, 12], [-6, -2], [-58, 5], [0, -12], [-16, 2], [40, 3], [48, -6], [48, 4], [-34, -2], [-10, -9], [-56, 4], [-10, 4], [2, -12], [-24, 2], [6, 3], [16, -12], [-16, -6], [-6, -3], [2, -10], [50, 4], [14, 11], [-6, 5], [-2, -13], [32, -12], [52, -2], [2, 12], [-56, 3], [8, 8], [-18, -8], [-30, 8], [12, 0], [66, 0], [22, -9], [10, 0], [30, -10], [8, 0], [12, 2], [-2, 6], [38, 6], [-30, -4], [16, 10], [-14, -4], [32, 3], [-22, -13], [-14, 2], [6, 2], [30, 1], [-44, 1], [-4, -10], [26, -8], [50, -3], [48, -6], [26, 10], [30, -2], [-6, 21], [60, -4], [44, -6], [24, -4], [-38, -4], [0, -2], [18, 11], [20, 7], [18, -12], [16, 6], [-30, 12], [6, -10], [-40, 10], [18, -4], [-14, 9], [-16, 3], [34, 0], [-36, -2], [38, -2], [0, 10], [28, 12], [-40, 11], [-6, 8], [48, 4], [-24, 6], [24, -12], [-18, -6], [12, -12], [10, -12], [-52, 10], [40, -1], [-32, -10], [54, 2], [-12, -13], [-12, 4], [-4, 6], [-6, -18], [12, 0], [6, -11], [-20, 9], [-6, -12], [-4, 16], [4, 15], [60, 7], [-30, 3], [14, 2], [-54, 10], [16, 0], [12, -4], [32, -12], [-62, 8], [-26, 0], [-6, 6], [-40, -6], [20, 0], [-56, 0], [0, 2], [-46, 12], [-18, 0], [2, -16], [44, -10], [16, -21], [-34, 6], [48, 5], [44, -10], [58, -8], [-32, -10], [30, 2], [-40, 6], [20, 10], [10, 0], [-32, -10], [26, -8], [-12, 1], [-4, -6], [2, -4], [-22, -4], [-28, 14], [-18, 3], [18, -20], [24, -12], [-70, -4], [-30, -16], [64, -4], [-30, 3], [20, 0], [-2, -18], [42, -16], [32, 12], [22, -10], [-20, 20], [24, 2], [72, -8], [58, -4], [-20, 10], [-16, 7], [60, -4], [-4, -22], [-56, -9], [0, -5], [26, 20], [-18, 2], [-14, 8], [-66, 9], [-14, 8], [8, -6], [-40, -6], [60, -2], [64, 1], [34, 3], [-24, -16], [-58, -6], [18, 4], [44, 0], [52, -4], [48, 8], [-4, -21], [20, -10], [28, 1], [12, -14], [-20, 1], [14, 18], [34, 4], [-28, -6], [10, -14], [48, -11], [24, -10], [50, 4], [42, 4], [-66, -1], [24, -22], [-18, 2], [6, -4], [0, 20], [-8, 20], [-60, 3], [28, 3], [-54, -1], [-70, 9], [42, 6], [-12, -14], [58, 8], [-30, -20], [32, 0], [40, -10], [-2, 14], [6, -18], [28, 10], [26, 8], [-12, 4], [62, 7]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_4830_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_4830_2_a_bt();".
// 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_4830_2_a_bt(:prec:=2)
    chi := MakeCharacter_4830_a();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(2999) - 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_4830_2_a_bt();".
// 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_4830_2_a_bt( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_4830_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<11,R![-8, 4, 1]>,<13,R![-12, 0, 1]>,<17,R![2, 1]>,<19,R![-4, 1]>,<29,R![4, 8, 1]>],Snew);
    return Vf;
end function;