
// Make newform 123.2.a.d in Magma, downloaded from the LMFDB on 24 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_123_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_123_2_a_d();".
// 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_123_2_a_d();".
// 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 := [2, -4, -1, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0], [0, 1, 0], [-3, 0, 1]];
    Rf_basisdens := [1, 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_123_a();"
function MakeCharacter_123_a()
    N := 123;
    order := 1;
    char_gens := [83, 88];
    v := [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_123_a_Hecke(Kf)
    return MakeCharacter_123_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 := [[0, 1, 0], [-1, 0, 0], [1, 1, -1], [1, -1, -1], [-1, -1, 0], [3, -1, 1], [1, -1, 2], [1, -1, 1], [-3, -1, 1], [-1, -3, 0], [-2, 4, 1], [6, 2, -1], [1, 0, 0], [4, -2, 5], [1, 1, 2], [6, -4, 2], [-2, -2, -2], [-2, -2, 1], [2, 6, -4], [-11, 1, 0], [2, -2, -3], [-8, 4, -2], [-5, 1, -3], [6, -4, 0], [-3, -3, 1], [-7, 3, 2], [4, 2, -3], [0, 8, -2], [3, -1, 1], [-7, 5, -5], [2, -6, 0], [3, 5, -1], [-9, 5, 2], [6, -6, -4], [2, -4, 8], [12, -4, 0], [2, 12, -4], [2, 8, -1], [6, -2, 0], [11, -1, -3], [-7, -3, -2], [6, 4, -2], [-6, 6, -6], [-1, -9, 1], [-5, -1, -7], [3, 1, 3], [-6, 2, 2], [8, -8, 8], [7, -5, 2], [-7, 5, 1], [-2, 12, -4], [-6, -2, -2], [-6, 6, 1], [-2, 10, 0], [9, -9, 2], [-17, 3, 0], [4, -2, 0], [16, -2, 1], [-4, 8, 3], [-3, -1, 4], [-8, 2, 5], [17, 7, -4], [2, 8, -1], [14, -6, 6], [-7, -3, -5], [3, 5, 6], [13, 3, -7], [-4, 0, 1], [3, -1, -6], [0, -8, 1], [10, -8, 8], [-7, -5, 1], [12, -6, 1], [12, -12, 5], [-14, 6, -4], [5, -7, -8], [-3, -3, 7], [3, 7, -3], [-2, -8, 2], [-20, 0, 5], [-9, 9, -1], [-2, 4, 2], [5, -1, 1], [-10, 2, 9], [-8, -4, -2], [24, 4, -4], [-28, 2, -4], [-22, -4, 2], [-6, 12, -8], [-9, 9, 5], [-8, 0, -6], [5, 5, 10], [18, 0, 9], [-3, -9, 3], [-10, 6, -2], [-13, 3, 10], [15, -3, 8], [-5, 17, -10], [-2, -6, -8], [18, -12, 8], [-6, -14, 2], [11, -3, -10], [3, -5, -8], [-5, 7, -13], [16, -4, -8], [16, -2, -4], [3, 3, 8], [-23, 3, 4], [-7, 19, -3], [-8, 2, -14], [12, 8, 2], [-4, -2, 0], [25, -3, 3], [10, -12, 9], [4, -2, -1], [-7, 11, -16], [2, 2, -10], [-9, 5, -9], [-11, -5, 8], [2, -6, 2], [18, -8, -6], [8, 2, -10], [7, -21, 1], [-6, -2, 8], [-9, 5, -3], [-12, -6, 2], [12, -6, 18], [5, -3, -2], [-23, 3, -7], [20, -4, 1], [-12, -14, -1], [4, -16, 6], [20, -8, -6], [-17, 7, -9], [24, -10, 8], [-20, 0, 1], [13, -17, -2], [-12, 6, 5], [12, 10, 6], [8, 18, -6], [-2, -4, -1], [-7, 5, 1], [6, 6, -12], [-17, 3, 14], [-2, 14, -7], [-22, 6, -2], [20, -10, 8], [-8, -10, 8], [-16, 2, -7], [27, 5, 5], [-8, 0, 17], [-34, 0, -2], [-19, -5, 1], [5, -15, 0], [-2, 10, 8], [-21, 1, 7], [1, -17, 7], [17, 11, -4], [2, -4, 14], [10, 12, 0], [-16, -8, 10], [7, -13, 11], [-16, -4, -6], [39, -9, 8], [25, -9, 2], [-5, 5, -15], [-6, -18, -2], [-35, -3, -1]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_123_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_123_2_a_d();".
// 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_123_2_a_d(:prec:=3)
    chi := MakeCharacter_123_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(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_123_2_a_d();".
// 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_123_2_a_d( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_123_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![2, -4, -1, 1]>],Snew);
    return Vf;
end function;