
// Make newform 768.2.f.b in Magma, downloaded from the LMFDB on 19 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_768_f();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_768_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_768_2_f_b();".
// 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_768_2_f_b();".
// 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 := [1, 0, 3, 0, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [1, 1, 1, 0], [0, 4, 0, 2], [-1, 1, -1, 0]];
    Rf_basisdens := [1, 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_768_f();"
function MakeCharacter_768_f()
    N := 768;
    order := 2;
    char_gens := [511, 517, 257];
    v := [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;

// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_768_f_Hecke();"
function MakeCharacter_768_f_Hecke(Kf)
    N := 768;
    order := 2;
    char_gens := [511, 517, 257];
    char_values := [[-1, 0, 0, 0], [-1, 0, 0, 0], [-1, 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 := [[0, 0, 0, 0], [-1, 0, 0, 1], [-2, -1, 0, 1], [0, -1, 0, -1], [0, -1, -2, -1], [0, 2, 1, 2], [0, 2, 0, 2], [2, -1, 0, 1], [0, -2, 0, 2], [6, -1, 0, 1], [0, 1, 2, 1], [0, 2, 3, 2], [0, 2, 2, 2], [6, 1, 0, -1], [-8, 0, 0, 0], [-2, -1, 0, 1], [0, 1, 0, 1], [0, -2, 1, -2], [6, 3, 0, -3], [8, 6, 0, -6], [2, 0, 0, 0], [0, -3, 2, -3], [0, -1, 2, -1], [0, 0, 2, 0], [-2, 2, 0, -2], [-2, 3, 0, -3], [0, -5, -4, -5], [0, 5, 4, 5], [0, -2, -3, -2], [0, 0, 4, 0], [0, 1, 6, 1], [0, 1, -4, 1], [0, -2, 2, -2], [-6, -3, 0, 3], [6, 3, 0, -3], [0, 3, 8, 3], [0, 2, 1, 2], [2, -5, 0, 5], [-16, 2, 0, -2], [14, 7, 0, -7], [0, 5, 0, 5], [0, -2, -9, -2], [-8, -4, 0, 4], [-2, -8, 0, 8], [6, -1, 0, 1], [0, -5, 0, -5], [-10, -1, 0, 1], [0, 5, 2, 5], [0, -5, 2, -5], [0, -2, 7, -2], [0, -4, -10, -4], [8, 0, 0, 0], [-2, 0, 0, 0], [0, 3, 10, 3], [0, 4, 8, 4], [-8, -2, 0, 2], [-10, -5, 0, 5], [0, -3, 2, -3], [0, 2, -5, 2], [0, 4, 10, 4], [-22, 1, 0, -1], [22, -1, 0, 1], [14, 11, 0, -11], [-8, 2, 0, -2], [-2, 2, 0, -2], [-2, -9, 0, 9], [-14, -15, 0, 15], [10, 10, 0, -10], [0, 3, 10, 3], [0, 2, 13, 2], [0, 8, 0, 8], [24, 6, 0, -6], [0, 1, 2, 1], [0, 6, -5, 6], [-2, -7, 0, 7], [24, 4, 0, -4], [-26, -5, 0, 5], [0, 6, 5, 6], [0, -10, -8, -10], [22, 8, 0, -8], [0, -5, -2, -5], [0, 6, 7, 6], [8, 0, 0, 0], [14, 2, 0, -2], [0, -5, -8, -5], [0, 3, -10, 3], [0, 6, -4, 6], [22, 0, 0, 0], [-2, -5, 0, 5], [0, 1, -18, 1], [0, -1, 6, -1], [-16, 8, 0, -8], [0, 7, 12, 7], [0, 13, 8, 13], [-26, -1, 0, 1], [-24, 2, 0, -2], [22, 3, 0, -3], [0, -10, -6, -10], [-18, 5, 0, -5], [0, -10, -7, -10], [-6, -1, 0, 1], [6, 7, 0, -7], [0, 15, 6, 15], [0, 2, 22, 2], [-6, 9, 0, -9], [26, 2, 0, -2], [0, -11, -4, -11], [0, 4, 12, 4], [0, 6, 0, -6], [-14, -16, 0, 16], [0, 1, -18, 1], [0, -14, -1, -14], [0, 8, 6, 8], [18, 9, 0, -9], [0, -9, -4, -9], [0, -14, -4, -14], [-22, 7, 0, -7], [-16, -14, 0, 14], [-18, 3, 0, -3], [0, -3, 16, -3], [0, -14, -17, -14], [-18, -6, 0, 6], [-18, 3, 0, -3], [0, -1, -6, -1], [26, 3, 0, -3], [-18, 3, 0, -3], [0, 2, -5, 2], [-16, -12, 0, 12], [0, -5, -4, -5], [0, -6, -11, -6], [-2, -9, 0, 9], [0, -6, 0, 6], [0, -11, -2, -11], [0, 6, -1, 6], [0, -18, -10, -18], [30, 16, 0, -16], [14, -5, 0, 5], [-22, -5, 0, 5], [-34, -13, 0, 13], [0, -6, 2, -6], [46, 5, 0, -5], [22, 23, 0, -23], [0, -9, -20, -9], [0, 9, 4, 9], [0, 2, 1, 2], [24, 6, 0, -6], [0, 14, 11, 14], [0, 10, -10, 10], [-18, 1, 0, -1], [-8, -12, 0, 12], [0, -6, 13, -6], [0, 0, 12, 0], [2, -1, 0, 1], [8, 10, 0, -10], [38, 1, 0, -1], [24, 8, 0, -8], [0, 15, 20, 15], [0, -6, -20, -6], [2, 10, 0, -10], [-2, 3, 0, -3], [0, 13, 4, 13], [0, 10, 6, 10], [0, -1, -4, -1], [0, -17, 2, -17], [0, 10, 24, 10], [-24, 2, 0, -2], [0, 5, 22, 5], [0, 10, 3, 10]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_768_f_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_768_2_f_b();".
// 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_768_2_f_b(:prec:=4)
    chi := MakeCharacter_768_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_768_2_f_b();".
// 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_768_2_f_b( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_768_f();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![-4, 2, 1]>,<19,R![4, -6, 1]>],Snew);
    return Vf;
end function;