
// Make newform 342.2.s.a in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_342_s();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_342_s_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_342_2_s_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_342_2_s_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
        poly := [4, 0, -2, 0, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]];
    Rf_basisdens := [1, 1, 2, 2];
    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_342_s();"
function MakeCharacter_342_s()
    N := 342;
    order := 6;
    char_gens := [191, 325];
    v := [3, 5];
    // 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_342_s_Hecke();"
function MakeCharacter_342_s_Hecke(Kf)
    N := 342;
    order := 6;
    char_gens := [191, 325];
    char_values := [[-1, 0, 0, 0], [1, 0, -1, 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, -1, 0], [0, 0, 0, 0], [0, -1, 0, 1], [-1, 2, 0, -1], [2, 0, -4, 2], [1, 3, 1, 0], [4, -1, -2, 1], [5, 0, -2, 0], [0, 4, 0, 0], [0, 1, 0, -2], [3, 0, -6, 3], [-1, 0, 2, -3], [0, 0, 0, 0], [0, -2, 1, -2], [-2, 1, -2, 0], [0, -2, 0, 4], [0, 1, 12, 1], [1, 1, -1, -2], [-1, -6, -1, 0], [0, 0, 6, 0], [0, -2, 7, -2], [6, -3, -3, 3], [6, 0, -12, -1], [0, -5, 0, 10], [-12, -6, 6, 6], [-6, -2, -6, 0], [1, 0, -2, -9], [6, 8, 0, -4], [0, -12, 0, 12], [0, -14, 0, 7], [0, 6, 0, 0], [4, 8, -2, -8], [-2, -2, -2, 0], [7, 0, -7, 0], [20, 2, -10, -2], [-4, 0, 8, -6], [0, -3, -5, -3], [-7, 12, 0, -6], [6, 1, -6, -2], [0, -5, 0, -5], [-12, 0, 0, 0], [-8, 6, -8, 0], [8, 0, -16, -1], [10, 6, -5, -6], [6, 0, -12, -7], [-5, -5, 5, 10], [14, -6, -7, 6], [2, -3, -1, 3], [-6, -14, 0, 7], [-7, -10, 0, 5], [-4, -10, 2, 10], [-4, 0, 8, 11], [13, -6, 13, 0], [0, 1, 0, 0], [-12, 0, 12, 0], [-12, 8, 6, -8], [0, 1, 18, 1], [0, -12, -2, -12], [14, -4, 0, 2], [-6, -7, 6, 14], [0, 2, 10, 2], [-18, 6, 0, -3], [-8, -6, 4, 6], [6, 0, -12, 11], [-8, -6, 8, 12], [0, 3, 0, -6], [1, 0, -2, -12], [22, -12, -11, 12], [-36, -1, 18, 1], [11, 10, 0, -5], [6, 0, -12, 5], [0, 8, 0, -8], [7, 3, -7, -6], [12, 0, -24, 6], [-11, 0, 22, 0], [0, -2, -6, -2], [12, 4, 12, 0], [0, 3, -29, 3], [0, 5, -12, 5], [-2, -18, -2, 0], [-6, 0, 12, -10], [-8, 6, 4, -6], [6, -9, -6, 18], [7, 12, 7, 0], [-2, -9, 1, 9], [-18, 1, -18, 0], [-6, -10, 0, 5], [5, 12, 0, -6], [4, 5, -2, -5], [23, 14, 0, -7], [4, 0, -8, -10], [6, -14, 6, 0], [-18, 0, 36, 6], [12, 14, -6, -14], [0, 10, 19, 10], [0, -29, 0, 0], [-6, -3, 6, 6], [-18, 8, 0, -4], [9, 0, 9, 0], [-23, -3, 23, 6], [-11, 12, -11, 0], [2, 16, 2, 0], [-6, -16, 0, 8], [36, -4, 0, 2], [11, -12, 0, 6], [-4, 8, 0, -4], [24, 5, -12, -5], [0, -11, 0, 0], [18, 8, -18, -16], [1, 0, -2, -6], [-11, 0, 22, -15], [0, -2, -14, -2], [-22, 4, -22, 0], [-7, -24, 0, 12], [-17, 1, 17, -2], [0, 9, 24, 9], [0, -8, -23, -8], [-4, 0, 8, -7], [14, 0, -28, -10], [-18, 12, 18, -24], [-6, -12, -6, 0], [-11, 0, 22, 0], [30, 6, 0, -3], [-6, -18, 0, 9], [14, -12, 0, 6], [0, 11, 0, -11], [1, -3, -1, 6], [0, 14, 0, -14], [0, 3, -17, 3], [-16, -12, 0, 6], [0, -12, -17, -12], [0, -12, -18, -12], [-1, 21, -1, 0], [0, -3, -17, -3], [-12, 0, 24, 17], [-17, 8, 17, -16], [-18, 11, 18, -22], [-9, 0, 18, 6], [-6, 36, 0, -18], [6, 0, -12, 11], [2, 12, 2, 0], [-4, -23, -4, 0], [-20, -6, 20, 12], [-6, -17, 6, 34], [-1, 0, 2, -9], [0, -9, 12, -9], [0, -3, 37, -3], [0, -7, 24, -7], [1, -2, -1, 4], [30, 6, 0, -3], [18, 9, -9, -9], [-2, 0, 4, -1], [1, 2, -1, -4], [-30, 3, 30, -6], [28, 12, -14, -12], [12, 0, 0, 0], [-13, 18, 0, -9], [-36, -7, 18, 7], [13, -12, -13, 24], [36, 2, -36, -4], [12, 20, -6, -20], [0, 2, -6, 2], [0, -3, -5, -3], [0, 17, -12, 17], [12, -10, 0, 5], [0, -10, 6, -10], [46, 15, -23, -15], [19, 9, -19, -18]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_342_s_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_342_2_s_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_342_2_s_a(:prec:=4)
    chi := MakeCharacter_342_s();
    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_342_2_s_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_342_2_s_a( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_342_s();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<17,R![100, -120, 58, -12, 1]>],Snew);
    return Vf;
end function;