
// Make newform 31.2.d.a in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_31_d();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_31_d_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_31_2_d_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_31_2_d_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 := [1, -1, 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_31_d();"
function MakeCharacter_31_d()
    N := 31;
    order := 5;
    char_gens := [3];
    v := [4];
    // 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_31_d_Hecke();"
function MakeCharacter_31_d_Hecke(Kf)
    N := 31;
    order := 5;
    char_gens := [3];
    char_values := [[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], [1, -1, 1, -1], [-1, 0, 1, -1], [0, 0, 3, 0], [0, -2, -2, -2], [0, 3, -3, 0], [-2, 2, 0, 3], [0, -5, 0, 0], [4, -4, 0, -1], [-1, 8, -1, 0], [0, -3, 2, -6], [-3, 0, -2, 2], [4, -4, 4, 0], [-1, 4, -1, 0], [5, -4, 4, -5], [6, -6, 0, 3], [-3, 7, -7, 3], [6, 0, 8, -8], [-1, 0, 2, -2], [-5, 5, 0, 8], [0, 9, -3, 9], [0, 0, 0, 0], [-5, 1, -5, 0], [0, -1, -7, -1], [0, -6, -9, -6], [2, -2, 0, -8], [3, 2, 3, 0], [-5, 5, 0, 7], [-11, -1, 1, 11], [0, 3, 0, 3], [-7, 9, -9, 7], [0, -5, -3, -5], [0, -4, 4, 0], [-1, 4, -4, 1], [4, 0, 13, -13], [0, 17, -9, 17], [6, -6, 6, 0], [6, -6, 0, 3], [-2, 8, -2, 0], [-9, 4, -4, 9], [0, -11, 13, -11], [17, 0, 0, 0], [-8, 0, 5, -5], [0, -1, -3, -1], [0, -12, 9, -12], [17, -23, 23, -17], [-8, 0, 0, 0], [-9, 0, -6, 6], [-19, 9, -19, 0], [-2, 6, -2, 0], [-1, 12, -12, 1], [12, -12, 0, -6], [0, -4, -11, -4], [12, -4, 4, -12], [-12, 12, 0, 18], [-7, -4, 4, 7], [1, 2, 1, 0], [-9, 9, 0, 5], [7, -9, 7, 0], [13, -11, 13, 0], [0, -9, 1, -9], [2, -2, 0, 5], [2, 3, -3, -2], [10, 0, -4, 4], [2, 0, 0, -2], [0, -16, 16, -16], [15, -2, 15, 0], [0, -21, 6, -21], [-21, 0, -18, 18], [6, -6, 0, 7], [1, 33, 1, 0], [14, -21, 21, -14], [-12, 0, 15, -15], [-23, 0, -14, 14], [0, 12, -11, 12], [0, 3, -15, 3], [26, -26, 0, -13], [26, 0, 6, -6], [-24, 15, -24, 0], [10, 0, 10, -10], [2, 2, -2, -2], [-18, 16, -16, 18], [-26, 28, -28, 26], [20, 0, 12, -12], [3, 0, -24, 24], [18, -18, 0, 12], [18, 8, -8, -18], [19, -19, 0, -15], [0, -19, -1, -19], [-18, 20, -18, 0], [-32, 13, -32, 0], [8, -8, 0, -4], [-29, 29, 0, 24], [8, 0, 22, -22], [-9, 6, -6, 9], [0, 3, 15, 3], [10, -5, 5, -10], [-11, 0, -26, 26], [0, -18, 23, -18], [0, 0, 0, -22], [0, 6, -20, 6], [10, 0, -16, 16], [6, 0, 9, -9], [0, 4, 18, 4], [-7, 7, -7, 7], [21, -26, 21, 0], [34, -15, 34, 0], [0, 16, 16, 16], [11, -23, 11, 0], [0, -22, 0, 0], [6, -18, 18, -6], [0, 8, 30, 8], [11, -13, 13, -11], [-40, 0, 0, 0], [0, -15, -18, -15], [-5, 38, -5, 0], [3, -3, 0, -13], [0, 16, -20, 16], [14, -31, 14, 0], [-27, 27, 0, 21], [-1, 16, -1, 0], [12, -12, 0, -15], [6, 0, -14, 14], [23, 0, 8, -8], [-24, 24, 0, 35], [-13, 22, -13, 0], [0, 3, 6, 3], [-43, 0, -1, 1], [24, -24, 0, -15], [0, -8, 23, -8], [12, 0, -6, 6], [-18, 0, -9, 9], [0, 24, -25, 24], [-14, 32, -32, 14], [-17, 17, 0, 24], [-23, 0, 19, -19], [-5, 16, -5, 0], [-6, -35, -6, 0], [8, -8, 0, -22], [-37, 48, -48, 37], [-9, 0, -32, 32], [26, -30, 30, -26], [18, -18, 0, -23], [-7, -7, -7, 0], [6, -6, 0, 12], [10, -5, 10, 0], [-4, 4, -4, 4], [0, 10, -2, 10], [6, -6, 0, -53], [30, 0, 17, -17], [6, -6, 0, -26], [-17, -3, 3, 17], [1, -1, 1, -1], [39, -15, 39, 0], [-29, 29, 0, -6], [10, -2, 10, 0], [0, 18, 21, 18], [-15, 0, -30, 30], [0, -38, 17, -38], [0, 12, 36, 12], [-26, 26, 0, 20], [-23, 23, 0, -5], [21, 0, -14, 14], [-9, 15, -9, 0], [-36, 10, -10, 36], [-13, 13, 0, 0], [7, 0, 15, -15], [31, 0, 36, -36]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_31_d_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_31_2_d_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_31_2_d_a(:prec:=4)
    chi := MakeCharacter_31_d();
    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_31_2_d_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_31_2_d_a( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_31_d();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([],Snew);
    return Vf;
end function;