
// Make newform 4020.2.a.f in Magma, downloaded from the LMFDB on 24 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_4020_a();"
// To make the coeffs of the qexp of the newform in the Hecke field type "qexpCoeffs();"
// To make the newform (type ModFrm), type "MakeNewformModFrm_4020_2_a_f();".
// 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_4020_2_a_f();".
// 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 := [144, 360, 209, -12, -28, -1, 1];
        Kf := NumberField(Polynomial([elt : elt in poly]));
        AssignNames(~Kf, ["nu"]);
    end if;
    Rf_num := [[1, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0], [348, 685, 180, -104, -17, 5], [-924, -1415, -204, 184, 19, -7], [492, 1055, 204, -160, -19, 7], [-708, -1103, -180, 160, 19, -7]];
    Rf_basisdens := [1, 1, 24, 48, 24, 24];
    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_4020_a();"
function MakeCharacter_4020_a()
    N := 4020;
    order := 1;
    char_gens := [2011, 2681, 3217, 1141];
    v := [1, 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;

function MakeCharacter_4020_a_Hecke(Kf)
    return MakeCharacter_4020_a();
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, 0, 0], [-1, 0, 0, 0, 0, 0], [1, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0], [-1, 0, 0, 0, 0, -1], [1, 0, 0, -1, 0, 0], [2, 0, 0, 1, 0, -1], [0, 0, -1, 0, 0, -1], [-1, 0, 1, 0, 1, 0], [1, 1, 1, 0, -1, 0], [0, 1, 0, -1, 0, 1], [3, 0, -1, 0, -1, 0], [1, 0, 0, 0, 1, 1], [1, -1, -1, 0, 0, 0], [0, 1, 0, 0, -1, 0], [2, -2, -1, 0, 0, -1], [1, 0, 0, 1, 0, 0], [2, 0, 1, 0, 0, 1], [1, 0, 0, 0, 0, 0], [-2, 0, 0, 1, 1, 1], [1, 1, 2, 0, -1, 1], [0, 2, 3, 1, 1, 2], [1, -3, -2, 0, -2, -1], [1, -1, 2, 0, 0, 1], [7, -1, -1, 1, 2, -1], [-1, -2, -1, 0, 1, -2], [1, -1, 1, 0, 2, 0], [0, 0, 0, 0, -1, 0], [3, -1, -4, 0, 0, -3], [2, 1, 2, -2, 0, 0], [5, -2, -1, 2, 0, -2], [-4, 0, 0, -1, 0, 1], [2, 0, 1, -2, 1, 3], [-3, 0, 2, -1, -1, 0], [4, 2, 1, -2, 2, 1], [4, -3, -5, 0, -1, -1], [5, -1, 1, 2, 1, 2], [7, 0, -1, 0, 0, 0], [0, 4, 2, 0, -1, 2], [5, -3, -1, -1, 1, -1], [-2, 1, 3, 0, 1, 1], [1, 3, 1, 0, 1, -2], [-3, 1, 2, 0, -3, -1], [10, 2, 1, 0, 1, 1], [1, 2, 2, 0, 2, 1], [-2, -1, 0, 0, -4, -2], [-1, 1, 4, 0, 2, 3], [9, -4, -2, 2, 1, -1], [-2, 3, 4, 0, 4, 2], [2, 2, 1, -2, -1, -1], [7, 1, 1, 2, 2, 0], [0, 2, 3, -2, -2, 5], [5, -2, -2, 4, 1, -1], [-6, 0, -2, 2, 1, 2], [6, -1, -3, 1, 0, 0], [5, 0, 2, -2, 3, 1], [5, -2, -4, -2, -1, -3], [2, -3, -3, -1, 2, 0], [6, -2, 0, 2, -1, -2], [2, -1, -1, 2, 3, 1], [8, 2, 0, -2, -1, 2], [0, 3, 4, 1, 0, 1], [3, -5, -1, 2, 2, -4], [-5, 1, 1, 4, 2, -4], [11, 3, 1, -1, -1, -1], [4, 0, -1, 3, -3, -2], [0, -1, -3, -3, -2, 4], [14, 0, -3, -1, 0, 2], [-7, 0, 1, -4, 1, 2], [5, 1, -2, 2, -4, -3], [4, 2, 4, 0, -3, 2], [5, -2, -5, 3, 0, 1], [5, 1, 4, 0, -2, 1], [15, 1, -4, -1, 0, 2], [0, -2, -6, -1, 0, -5], [5, -4, -4, 0, -1, 1], [5, -4, -2, 0, 0, -3], [1, 1, 3, -4, 2, 2], [-9, 5, 1, -2, -2, 2], [-1, 0, 3, -4, 1, 4], [-2, -6, 4, 1, 1, 1], [3, 0, 1, 2, 0, -6], [-9, 9, 1, -1, 0, 1], [7, -6, -5, 1, -2, -1], [4, 1, 6, 0, 0, 6], [0, -3, -3, -2, -1, 3], [1, 0, 1, 2, 0, -2], [13, 0, -1, -2, 0, 0], [-5, -4, 0, 0, 2, 1], [20, -2, 1, 2, 0, -1], [-8, -3, -4, -4, 2, 0], [0, -7, -2, -1, 3, -1], [-6, -5, -1, 2, -3, -1], [-19, -5, -4, -1, 0, -2], [2, -4, 1, -1, -4, -4], [-12, 7, 7, -2, -2, 3], [-4, 3, 5, 2, 3, -3], [-16, 7, 7, 0, 0, 5], [8, -5, 3, -2, 0, 3], [-5, 1, 2, -2, 7, 5], [-1, -4, -6, 2, -4, -1], [-8, 3, -5, 3, 0, -6], [-4, -3, -1, 4, -1, -7], [6, -2, 0, -2, -3, -2], [-4, -5, -3, 2, 4, -1], [2, 9, 2, -1, 1, 3], [-17, 2, 2, 0, 0, -1], [2, 3, 2, 0, 1, 2], [-8, -1, -2, -4, -5, -2], [-8, 1, -1, 0, 0, -5], [-8, -1, 2, -2, -1, 4], [2, -1, 1, 0, -2, 1], [-2, 5, -2, -3, 1, 1], [2, 7, 3, 2, -2, 7], [-2, -1, -3, 1, 1, -2], [0, 3, -1, -4, -4, 7], [11, 3, 0, 2, 0, -3], [-18, -2, 2, 2, 4, 0], [-7, 2, -4, -2, 1, -3], [-7, -5, 2, 3, -2, -4], [-4, -3, -2, 0, -6, -4], [2, 6, 3, 1, -2, -2], [-7, 2, 6, 0, -6, 1], [-5, 3, 7, 2, 1, 6], [2, 2, -3, 4, -1, 3], [-20, -5, -2, 0, 2, 4], [-1, -6, 1, 2, 4, 2], [-3, 1, 3, 3, 6, 5], [-7, -2, -2, 4, 6, 3], [9, 4, -1, 1, -4, 1], [-8, 7, 6, -1, 1, -1], [-15, -2, 2, 4, 2, 3], [7, 0, -4, 0, -3, -1], [-21, 1, 5, 5, 2, 1], [-7, -4, -1, -4, -3, -2], [-1, -3, -3, -2, -7, 0], [-19, 5, 3, -3, 2, 1], [-12, -1, -5, -2, -3, -3], [2, 7, 5, 1, 3, 4], [-6, -5, -3, -6, -1, -5], [-13, 3, 0, 3, 1, -4], [-10, -2, 4, 0, 2, 0], [8, 7, 6, -2, -2, 6], [-21, 1, -3, -2, -2, 2], [-11, 2, -4, 2, 0, -1], [-2, 3, 1, -7, -3, 6], [-2, 6, -2, -2, 4, 4], [14, -2, 1, 6, 2, 3], [-2, -8, -2, 0, -2, -8], [11, -6, 0, 2, -4, -7], [3, -2, -4, 4, 2, 1], [-2, 1, 2, -4, -3, 10], [9, 4, -4, 0, -5, -7], [-7, 5, -4, -6, 3, 7], [-10, -6, -6, -2, -2, -4], [6, 3, 5, 1, 2, -2], [-1, -3, 3, -1, 0, 7], [3, 4, 10, 4, 3, 7], [3, 1, -5, -3, -9, -1], [-11, -5, -2, 0, 1, 7], [2, -3, 1, 0, 3, -1], [-8, -1, 4, 3, 3, -1], [0, 7, 2, 2, 0, 6], [0, 0, -4, 3, 0, -3], [-5, -10, -5, -1, -2, -7], [8, -5, -6, 4, 5, -4], [4, -4, -1, -1, -1, -4], [5, -9, -10, 2, -5, -5], [-18, -3, 2, 0, 2, 6], [10, -5, -7, -2, -8, -5], [0, -6, -5, -1, 3, -4], [-3, -6, -3, 4, -3, -12], [9, 1, -2, 3, 0, 4], [-8, 2, 0, -1, -4, -9], [4, 1, -4, -3, 3, 7], [3, 1, -9, -2, -4, -6], [-24, -2, 4, 1, -3, -1], [3, -11, -6, 2, -1, -3], [14, -7, -8, 0, 3, -10], [4, -4, -9, 4, -2, -3], [7, 0, 5, -6, -2, -2], [15, -3, 1, 11, 0, -7], [3, 1, 3, 4, 2, -4], [6, -6, 0, 1, 1, 3], [-3, 1, -6, 2, -6, -3], [26, 5, 1, 2, 1, 3], [2, 0, -9, -1, 3, 4], [2, 0, -5, 4, -4, -7], [-14, -1, 0, -4, -2, 8], [-6, -5, 4, -2, 2, 0], [11, -6, 4, 0, 6, 1], [-5, -1, 5, -2, -3, 2], [13, 6, 2, -1, 9, 8], [5, -6, -3, 8, -3, -8], [-5, 8, 9, -4, -4, 10], [-12, 2, 6, 5, 6, -1], [3, -2, -2, 2, 6, -3], [12, -14, 1, 1, -1, -2], [19, 1, 4, 2, 5, 7], [15, -8, -9, 6, -1, -12], [-15, -2, 5, 0, -3, 0], [3, -2, 1, -4, -2, -4], [-8, -6, 2, -1, 5, 1], [-21, -2, 4, 0, -2, 1], [13, 5, -8, -2, 2, -1], [9, -1, -6, 7, -1, -6], [-8, 2, 6, -4, -2, 6], [-5, -5, 3, 0, 6, 6], [15, -6, 0, 0, 0, 9], [-10, -5, 8, 1, 7, 5], [5, -9, 3, 0, 0, -6], [-15, 8, 5, -6, -4, -4], [11, -10, 0, -2, 5, -3], [-6, 1, -8, -6, 3, 4], [3, 4, 5, 0, 5, 0], [7, -2, 2, 4, -2, 3], [2, -11, -7, 4, 1, 5], [-8, 7, 13, -4, 8, 7], [-3, 7, -3, -4, -3, -6], [-19, 2, 5, -5, -2, 13], [22, -7, -1, 4, -2, -1], [10, -1, 4, -12, 0, 6], [38, 2, 2, 4, 0, 2], [17, 2, -2, 4, 6, 9], [-30, -4, 1, 4, -1, 5], [-11, 1, -1, -2, -4, 2], [16, 9, -4, 1, -6, -3], [17, -4, 5, 0, -1, -6], [12, -1, -5, -12, -6, -1], [-2, -3, -2, -2, -6, 6], [-2, -5, 3, 5, 1, -2], [-15, 0, -5, -1, -4, -7], [9, -2, 0, 0, -4, 1], [-9, -2, -3, 2, 0, -8], [5, 6, 4, 2, 0, 7], [18, -11, -7, -2, -1, -3], [0, -2, -5, -4, 2, -7], [5, -1, -1, -1, 1, -1], [-5, -2, -7, 5, 2, -1], [22, -9, -5, 1, 0, 4], [-19, 7, 2, -2, -6, 5], [-2, 0, 7, 7, 4, -2], [21, -9, -3, -4, -2, -2], [10, 4, -1, 2, 5, 5], [8, -1, -7, -6, 2, -3], [7, 8, 11, -4, -1, 2], [18, 2, -10, 0, -8, -8], [-11, 2, -8, 4, 6, -3], [-2, 6, 0, -5, 3, -1], [4, 1, -5, 2, -5, 5], [2, 5, 4, -2, -8, -2], [12, -3, -11, 2, -1, -11], [-29, 10, 7, -2, 5, 6], [-20, -3, 5, -2, 9, 7], [-11, 7, 4, -6, -7, 9], [26, 4, 1, -2, 1, -3], [20, -2, -8, 2, -6, -4], [3, 8, 9, 0, 10, 6], [3, -11, -4, -3, -2, -8], [-6, 1, -4, 2, -5, -2], [8, 0, 8, -4, 5, 6], [-9, -5, 8, 4, 2, 3], [11, 0, -9, 6, -4, -2], [2, -11, 3, 7, -3, 0], [13, -13, -8, 5, 4, -2], [-11, 6, -1, -8, 0, 4], [-20, 10, 1, 0, 0, -3], [-1, -9, -9, 0, 1, -10], [-8, 5, 6, -8, -3, 2], [-20, 1, 1, -2, 6, 5], [22, 9, 4, -2, 4, 6], [-10, 2, -2, 0, -5, -12], [-22, 9, -1, -1, 3, 8], [40, -11, -4, 8, 5, 0], [-2, 6, 5, 2, 7, 7], [3, -4, 0, -4, -3, 7], [-20, 1, 5, 0, -2, 9], [-20, 2, 10, 6, 3, -6], [-20, 7, 12, -2, 3, 10], [9, 0, -1, 0, -2, -4], [5, -12, -4, 2, 0, -9], [-18, 4, 12, -2, -3, 8], [7, 4, -2, 0, 1, 13], [-9, 3, -2, 0, 0, -1], [-15, 7, 4, 2, -3, 7], [41, 5, -1, 3, -4, -3], [-10, -3, -3, 8, -2, 1], [-13, -1, 4, -1, -1, -2], [-20, -7, -8, 3, -4, -15], [51, -3, 7, -6, -6, 2], [-19, 4, 5, 6, 0, -2], [-11, -1, 5, 6, -1, -2], [-9, 11, 11, 1, 2, 3], [-6, -6, 9, 11, 1, 0], [-6, 10, -1, 3, -2, 4], [3, -2, -8, 2, -9, -1], [20, -9, 4, -1, -3, 5], [-12, 2, 3, -10, -3, 11], [-15, 1, 14, 3, -7, 4], [-21, 1, 10, -2, 3, -1], [-9, -14, -1, 3, 3, 5], [0, -3, -5, -7, -11, -4], [-11, 4, 8, 0, 9, 5], [-9, -5, -9, -12, -2, 2], [1, -18, -11, 0, -5, 2], [9, 1, -13, -7, -1, -3], [-23, -1, 5, -2, 0, -8], [14, -4, -6, -4, -2, -6], [20, 10, 6, 3, 1, 11], [-18, -6, 0, -7, 3, 11], [12, -13, -4, 0, 2, -4], [1, -7, 1, 0, 9, 4], [21, 7, 0, 2, -8, 1], [-7, -2, -2, 6, 0, -7], [-5, -6, 1, -2, 3, 10], [-1, 0, 5, 4, -4, 6], [27, 0, -3, 3, 0, -3], [-25, -10, -4, -2, 3, -7], [-34, 6, -5, -4, 2, 3], [-17, -5, -5, 4, -3, -4], [-7, -13, -3, 0, 2, -6], [25, -7, 0, 6, 4, 1], [-2, -5, -2, -2, 1, 16], [9, -4, 7, 0, -7, 4], [9, 7, -9, -1, 5, 7], [9, 7, 6, -4, 3, 9], [6, 17, 11, 0, 0, -3], [15, 1, -6, -8, -10, -5], [-1, -6, 5, 6, 2, -6], [17, 5, 8, 4, 9, 11], [25, -11, -6, 6, 10, -19], [12, 7, 4, 1, 1, 17], [30, -9, -1, 1, 4, 4], [30, -3, -16, -4, -1, -8], [-9, 1, -5, -4, -2, 10], [4, -3, -16, -4, -1, -12], [-13, -17, -11, -2, -1, 4], [6, 4, -4, -1, 0, 5], [-24, 10, 3, -10, -2, 7], [11, -7, 4, -2, 2, 1], [8, 2, -3, 2, -9, 1], [19, -11, -4, 3, -2, -2], [7, 9, 2, -8, 3, 3], [-10, 6, -12, -2, -1, -12], [-4, 9, 14, 1, 0, 7], [12, 4, -6, -4, 6, 6], [-6, 7, 10, -6, -7, 4], [24, 2, 5, 0, 6, -3], [-1, 2, 2, -5, 5, -2], [16, 3, 11, 0, -2, 9], [20, -3, 1, 2, 2, -9], [-11, 0, -3, 9, 6, 7], [-21, -9, -18, 2, 0, -19], [13, 4, 1, 8, 1, -18], [-1, 7, 12, 0, -7, 5], [7, -11, -2, 8, 0, -5], [27, -11, 2, 9, 6, 4], [-1, -5, 4, -6, -4, 1], [12, -3, 6, -8, 3, -4], [-16, 8, 13, -8, 0, 5], [-3, 0, 6, -14, 4, 3], [13, -5, -1, 14, 0, -8], [2, 9, 7, 6, 9, 3], [-10, 3, -6, -5, -5, 1], [32, 6, 0, -6, -4, 8], [16, 6, 1, -5, 3, -4], [30, -16, -15, 1, -1, -12], [19, -9, -12, 2, 3, -13], [8, 9, 0, 6, -2, 0], [-17, 4, -2, 0, -8, 13], [24, -10, -14, 4, -5, -2], [13, -9, -3, 4, -9, -6], [-20, 12, -5, 2, 5, 1], [-2, -6, 12, -1, 5, 19], [-10, -2, -6, 11, 4, -1], [11, -10, -2, -5, 1, 2], [18, -7, 0, 0, 2, 6], [-23, 17, 6, 2, 7, 7], [15, -18, -12, -2, -6, -9], [20, -2, -3, 4, 2, -1], [36, -1, -7, 0, 0, -9], [-61, 21, 13, -10, -3, 12], [-8, 3, 12, -4, 2, 12], [14, 15, 14, 8, -2, 2], [-31, -4, -7, -1, -2, 7], [-22, 4, 5, -4, 0, -5], [-5, -5, -5, -1, 7, -9], [-8, 4, 5, -2, -4, -3], [5, 5, 4, 0, 4, 1], [-7, -1, 7, 14, 4, 2], [-59, -5, -1, 0, -3, -8], [15, -18, -6, -6, 3, -7], [42, 6, 2, -3, 3, 7], [14, -1, -13, -8, 2, -3], [15, -4, 0, -6, 5, -3], [-51, -2, -6, -2, 3, -1], [33, -8, -8, 0, -4, -3], [26, -5, -1, 2, 4, -3], [-8, 4, 11, -11, 10, 14], [-7, 1, -9, 2, 0, 2], [16, -8, 0, 14, 0, -16], [-11, 3, -11, -3, 6, -1], [16, 8, -1, -4, -7, -1], [0, 18, 3, 6, -5, 11], [-19, -2, 11, 4, -9, 2], [17, -5, -5, 3, 5, 1], [-25, 3, 4, -1, 2, -6], [-28, -1, -4, 2, 3, -4], [11, 12, -10, -4, -1, -7], [0, 0, -12, 12, -3, -12], [-3, 8, -1, -10, -8, 4], [33, 2, -7, 3, 2, -7], [-9, -12, -12, -2, -4, -15], [10, -5, -1, 8, 1, 9], [-52, -9, -3, -3, 6, 6], [-11, 5, 1, 8, 4, 8], [34, 0, 2, -5, -2, 9], [1, 3, 10, -10, 6, 5], [7, -2, -8, -7, -8, 4], [5, 10, 1, -2, -14, 4], [16, 7, 0, 4, 8, 4], [6, 5, -5, -8, 10, 3], [-15, 3, -6, 10, -4, -7], [-7, 7, 13, -8, -6, 18], [-43, 0, 10, 5, 4, 4], [29, -3, 1, -5, 2, 1], [1, 0, 3, -8, -1, -4], [-5, -9, 1, -10, 0, -4], [-2, 14, -1, -4, -3, -3], [8, 5, 2, -8, 6, 2]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_4020_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_4020_2_a_f();".
// 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_4020_2_a_f(:prec:=6)
    chi := MakeCharacter_4020_a();
    f_vec := qexpCoeffs();
    Kf := Universe(f_vec);
    // SetVerbose("ModularForms", true);
    // SetVerbose("ModularSymbols", true);
    S := CuspidalSubspace(ModularForms(chi, 2));
    S := BaseChange(S, Kf);
    maxprec := NextPrime(2999) - 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_4020_2_a_f();".
// 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_4020_2_a_f( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_4020_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<7,R![144, 360, 209, -12, -28, -1, 1]>],Snew);
    return Vf;
end function;