
// Make newform 4.6.a.a in Magma, downloaded from the LMFDB on 19 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_4_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_4_6_a_a();".
// 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_4_6_a_a();".
// 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
        Kf := Rationals();
    end if;
    return [Kf!elt[1] : elt in input];
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_4_a();"
function MakeCharacter_4_a()
    N := 4;
    order := 1;
    char_gens := [3];
    v := [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_4_a_Hecke(Kf)
    return MakeCharacter_4_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 := 6;
    raw_aps := [[0], [-12], [54], [-88], [540], [-418], [594], [836], [-4104], [-594], [4256], [-298], [17226], [-12100], [-1296], [19494], [-7668], [-34738], [21812], [-46872], [67562], [-76912], [67716], [29754], [-122398], [11286], [-27256], [122364], [99902], [-29646], [336512], [100980], [-317142], [-148324], [196614], [74360], [120878], [-111340], [-491832], [707454], [493668], [-559450], [-724032], [7106], [-530442], [56168], [-339196], [779360], [-744876], [-272746], [-153846], [1154736], [657074], [1341900], [132354], [943272], [967518], [-518320], [2222726], [-196614], [-1552276], [-1072170], [1585892], [-730728], [584858], [-2482866], [377948], [639122], [-2904660], [-3991570], [1429218], [1161864], [-1089232], [3505766], [4043852], [5187456], [-950346], [-520738], [764370], [2640506], [-4980204], [-237994], [-3882384], [-66958], [-6501352], [-4607604], [3776706], [-3180694], [6685470], [-4351216], [7079940], [3221856], [2297096], [2821500], [-4136284], [8332632], [4341006], [-6741846], [-7721956], [-682066], [2157716], [-2675970], [-3553308], [-12922470], [-6083572], [-15824062], [4602204], [8611218], [-7982280], [10174010], [-9958432], [4195862], [9125514], [6457340], [-14051368], [8471682], [488564], [2481192], [-5291298], [4724676], [-6174202], [-9409246], [15008598], [-12970692], [22655588], [19016910], [15131126], [-15032304], [-7412296], [-2779282], [-12104620], [4469256], [28846256], [9608678], [4545882], [-21592318], [-14840010], [-24878524], [31607982], [-3100086], [1871804], [-20018394], [15311768], [9593100], [25220942], [-17762328], [-486970], [-1926342], [22353836], [18583776], [-29104834], [-3146958], [15999524], [-34587432], [17439644], [-2595888], [-17641096], [39678498], [39341258], [46250622], [-37902492], [-26646246], [40979048], [-27203364], [25355538], [11913912], [29193056], [-17300074]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_4_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_4_6_a_a();".
// 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_4_6_a_a(:prec:=1)
    chi := MakeCharacter_4_a();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 6));
    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_4_6_a_a();".
// 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_4_6_a_a( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_4_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,6,sign)));
    Vf := Kernel([],Snew);
    return Vf;
end function;