
// Make newform 637.2.h.g in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_637_h();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_637_h_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_637_2_h_g();".
// 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_637_2_h_g();".
// 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, 2, -1, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0], [0, 1, 0, 0], [1, 0, 0, 1], [-1, -2, 2, -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_637_h();"
function MakeCharacter_637_h()
    N := 637;
    order := 3;
    char_gens := [248, 197];
    v := [2, 2];
    // 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_637_h_Hecke();"
function MakeCharacter_637_h_Hecke(Kf)
    N := 637;
    order := 3;
    char_gens := [248, 197];
    char_values := [[0, 0, 0, 1], [0, 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 := [[1, 0, -1, 0], [0, -1, -1, -1], [0, 1, 1, 1], [0, 0, 0, 0], [0, 3, 3, -3], [-4, 0, 0, -3], [5, 0, 4, 0], [-3, 3, 0, -3], [2, 0, 4, 0], [1, -5, 0, 1], [-5, 6, 0, -5], [4, 0, 0, 0], [-4, 2, 0, -4], [0, 9, 9, -2], [0, -2, -2, 1], [-7, 2, 0, -7], [1, 0, 2, 0], [6, 0, 0, 6], [0, -6, -6, -3], [0, -10, -10, 2], [2, 0, 0, 2], [0, 0, 0, 4], [-3, 0, -6, 0], [13, 0, 5, 0], [0, 3, 3, 14], [0, -9, -9, 3], [0, -6, -6, 1], [-5, 0, -1, 0], [-7, 6, 0, -7], [0, 4, 4, -5], [16, 3, 0, 16], [0, -7, -7, -4], [-1, 0, 1, 0], [0, 9, 9, -10], [3, -3, 0, 3], [11, -6, 0, 11], [-10, -3, 0, -10], [-6, 6, 0, -6], [-11, -2, 0, -11], [9, 0, 0, 9], [0, 0, 0, -9], [0, 0, -6, 0], [-23, 1, 0, -23], [0, 0, 0, -6], [-1, 11, 0, -1], [-5, 0, 12, 0], [5, -6, 0, 5], [4, -15, 0, 4], [-5, 0, -4, 0], [0, -18, -18, 16], [0, 1, 1, 1], [-15, 0, 6, 0], [10, 0, -9, 0], [0, -2, -2, 4], [-14, 0, -19, 0], [0, 0, 0, 9], [2, 0, 19, 0], [11, 0, 12, 0], [-5, 0, 0, 0], [4, 0, -10, 0], [0, 12, 12, -6], [0, 2, 2, -10], [0, 0, 3, 0], [8, -7, 0, 8], [0, 18, 18, -4], [0, 2, 2, 23], [15, -3, 0, 15], [3, 0, 9, 0], [34, 0, 2, 0], [-11, -6, 0, -11], [0, -3, -3, 27], [0, -5, -5, -14], [0, -12, -12, 18], [6, 9, 0, 6], [11, -3, 0, 11], [-12, 21, 0, -12], [-14, 16, 0, -14], [18, -12, 0, 18], [-5, 0, -25, 0], [29, 0, 9, 0], [-1, 8, 0, -1], [-18, 0, -12, 0], [0, 11, 11, -10], [0, 0, 0, 1], [10, 0, -3, 0], [0, -2, -2, -2], [0, -4, -4, 26], [-4, 0, -12, 0], [0, -23, -23, 25], [-3, 0, -6, 0], [0, -14, -14, 25], [0, 21, 21, -9], [-4, 0, -21, 0], [-14, 1, 0, -14], [0, 3, 3, 10], [0, 1, 1, 25], [17, 0, 22, 0], [4, -14, 0, 4], [-28, 0, -18, 0], [0, 15, 15, 11], [-3, 0, 0, 0], [0, -21, -21, 6], [-34, 0, -8, 0], [2, 0, -8, 0], [19, -27, 0, 19], [5, 24, 0, 5], [28, -5, 0, 28], [0, 11, 11, 26], [-2, -17, 0, -2], [13, -33, 0, 13], [23, 0, 0, 23], [0, 9, 9, 20], [0, -8, -8, 13], [10, -12, 0, 10], [0, 33, 33, -19], [-20, 0, 17, 0], [0, 0, 0, -7], [0, -2, -2, 28], [-2, 0, -1, 0], [0, -16, -16, 2], [0, -30, -30, 0], [-19, 36, 0, -19], [0, 19, 19, 13], [-5, 0, -4, 0], [-1, 0, 3, 0], [8, 0, -2, 0], [-9, -9, 0, -9], [21, -18, 0, 21], [-21, 0, 6, 0], [0, -15, -15, -8], [0, 18, 18, -36], [-28, -7, 0, -28], [13, 0, -6, 0], [-28, 0, 0, -28], [24, 3, 0, 24], [-1, 12, 0, -1], [-7, 0, -20, 0], [22, 0, 12, 0], [0, -10, -10, 8], [0, -12, -12, 15], [15, 0, -15, 0], [25, 0, 20, 0], [-19, 0, 12, 0], [-18, 0, -21, 0], [0, 9, 9, -7], [0, 19, 19, -17], [-15, 0, -18, 0], [-14, 25, 0, -14], [0, -36, -36, 14], [0, 16, 16, -14], [9, -6, 0, 9], [1, 22, 0, 1], [29, 0, 0, 0], [32, 0, -14, 0], [0, 0, 0, -24], [21, 0, 27, 0], [30, 0, 0, 30], [31, -26, 0, 31], [-45, 0, -18, 0], [-43, 14, 0, -43], [23, 0, 37, 0], [0, 32, 32, -25], [-39, 0, 0, 0], [-51, 12, 0, -51], [0, 4, 4, -29], [-20, 1, 0, -20], [0, 3, 3, -21], [49, 0, 0, 0]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_637_h_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_637_2_h_g();".
// 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_637_2_h_g(:prec:=4)
    chi := MakeCharacter_637_h();
    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_637_2_h_g();".
// 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_637_2_h_g( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_637_h();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![1, -3, 1]>,<3,R![1, -3, 8, -3, 1]>,<5,R![1, 3, 8, 3, 1]>],Snew);
    return Vf;
end function;