
// Make newform 1008.2.cs.c in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1008_cs();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_1008_cs_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_1008_2_cs_c();".
// 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_1008_2_cs_c();".
// 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, -1, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rfbasis := [Kf.1^i : i in [0..Degree(Kf)-1]];
    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_1008_cs();"
function MakeCharacter_1008_cs()
    N := 1008;
    order := 6;
    char_gens := [127, 757, 785, 577];
    v := [3, 6, 6, 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_1008_cs_Hecke();"
function MakeCharacter_1008_cs_Hecke(Kf)
    N := 1008;
    order := 6;
    char_gens := [127, 757, 785, 577];
    char_values := [[-1, 0], [1, 0], [1, 0], [0, 1]];
    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], [-2, 1], [-1, -2], [-1, -1], [0, 0], [3, 3], [0, 7], [10, -5], [6, 0], [5, -5], [0, 5], [-4, 8], [2, -4], [0, -3], [-9, 9], [-9, 9], [10, -5], [-3, -3], [2, -4], [1, 1], [6, -3], [12, 0], [14, -7], [4, -8], [3, 3], [0, -1], [-6, 3], [-11, 11], [-6, 0], [-2, 4], [0, 21], [3, -3], [4, 0], [0, -9], [-7, -7], [9, 9], [14, -7], [12, 0], [-10, 5], [-9, -9], [-4, 8], [-14, 7], [5, -5], [6, 0], [-11, 11], [-14, 28], [-16, 0], [-21, 21], [-14, 7], [0, 3], [6, -12], [-7, -7], [0, 0], [22, -11], [-5, -5], [-1, -1], [0, -1], [17, -17], [-6, 0], [-11, 11], [12, -24], [20, 0], [-33, 33], [34, -17], [0, -21], [-34, 17], [14, 0], [-5, -5], [16, -32], [11, 11], [18, -9], [1, -1], [0, 13], [6, -12], [0, -27], [-21, 21], [-14, 7], [0, 3], [-3, -3], [12, 0], [10, 0], [-17, -17], [-20, 40], [0, 19], [26, -13], [18, 0], [0, 1], [-16, 32], [-2, 4], [0, -3], [-9, 9], [5, 5], [10, -20], [14, -7], [24, 0], [-18, 9], [-17, -17], [0, 23], [0, -7], [14, -28], [3, -3], [15, -15], [0, 39], [-7, -7], [9, 9], [-12, 0], [22, -11], [19, 19], [-4, 8], [0, -29], [-11, 11], [18, 0], [-7, 7], [-26, 52], [-9, 9], [-4, 0], [15, -15], [0, 3], [14, -28], [-23, -23], [-50, 0], [46, -23], [-25, -25], [0, -13], [-30, 0], [0, -35], [0, 33], [-32, 0], [-22, 11], [1, 1], [-22, 44], [46, -23], [26, 0], [6, -3], [-4, 8], [-5, -5], [-7, 7], [-8, 16], [15, -15], [4, 0], [0, -57], [13, 13], [22, -44], [5, 5], [0, 0], [-8, 16], [-25, -25], [0, -41], [-54, 27], [0, -47], [8, -16], [26, -52], [0, -3], [-3, -3], [-6, 12], [-50, 25], [30, -15], [24, -48], [-17, -17], [34, -17], [18, 0], [-18, 36], [0, -3], [27, -27], [3, -3], [-3, -3], [1, 1], [-50, 0], [-58, 29], [-21, -21], [24, -48], [-6, 3], [17, -17], [37, -37], [4, -8], [-10, 20], [-9, 9], [-56, 0], [2, -1], [-10, 5], [-36, 0], [22, 0], [-18, 9], [11, 11], [-1, -1], [37, -37], [5, -5], [0, 53], [-21, 21], [50, -25], [-18, 36], [22, -11], [-66, 33], [23, 23], [-13, -13], [5, -5], [0, 41], [-20, 40], [0, -15], [51, -51], [-16, 0], [26, -13], [-11, -11], [-36, 0], [39, 39], [0, -17], [10, -5], [6, 0], [25, -25], [0, 13], [-32, 64], [38, -76], [0, -51], [51, -51], [-54, 27], [9, 9], [-5, -5], [-14, 7], [66, 0], [0, -23], [52, 0], [0, 39], [-66, 33], [-12, 0], [-62, 0], [22, -11], [35, 35], [0, -37], [-62, 31], [49, -49], [49, -49], [-26, 52], [-21, 21], [-52, 0], [39, -39], [-38, 19], [0, -33], [6, -12], [-12, 0], [43, 43], [0, -25], [49, -49], [0, -43], [-32, 64], [0, 9], [-32, 0], [3, -3], [-39, -39], [38, -76], [2, 0], [30, -15], [-33, -33], [-36, 72], [-17, -17], [-38, 19], [41, -41], [-35, 35], [0, 0], [-6, 3], [37, 37], [14, -28], [45, 45], [0, 0], [-5, -5], [0, 71], [30, 0], [12, -24], [-6, 12], [51, -51], [-94, 47], [1, 1], [-43, -43], [78, -39], [36, -72], [0, -25], [82, -41], [-31, 31], [0, 17], [0, 57], [75, -75], [-31, -31], [-72, 0], [-24, 48], [0, -49], [2, -1], [-23, 23], [6, 0], [-7, 7], [-4, 8], [-21, 21], [-45, 45], [0, -33], [-72, 0], [26, 0], [-13, -13], [0, 43], [-24, 48], [0, 21], [-56, 0], [2, -1], [0, -57], [-15, -15]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1008_cs_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1008_2_cs_c();".
// 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_1008_2_cs_c(:prec:=2)
    chi := MakeCharacter_1008_cs();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(1999) - 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_1008_2_cs_c();".
// 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_1008_2_cs_c( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1008_cs();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![3, 3, 1]>,<11,R![3, 3, 1]>,<13,R![0, 1]>,<17,R![27, -9, 1]>,<19,R![49, -7, 1]>],Snew);
    return Vf;
end function;