
// Make newform 847.2.f.c in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_847_f();"
// To make the character of type GrpDrchElt with Codomain the HeckeField, type "MakeCharacter_847_f_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_847_2_f_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_847_2_f_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, -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_847_f();"
function MakeCharacter_847_f()
    N := 847;
    order := 5;
    char_gens := [122, 365];
    v := [5, 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_847_f_Hecke();"
function MakeCharacter_847_f_Hecke(Kf)
    N := 847;
    order := 5;
    char_gens := [122, 365];
    char_values := [[1, 0, 0, 0], [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 := [[-2, 1, -1, 2], [0, 1, -1, 1], [0, -1, 0, 0], [0, 0, 0, 1], [0, 0, 0, 0], [2, 0, 0, -2], [-5, 0, -5, 0], [0, 2, 3, 2], [-3, 0, -5, 5], [-1, 1, 0, -3], [1, -3, 3, -1], [-4, 4, 0, 0], [0, -10, 5, -10], [-2, 0, -9, 9], [0, 1, -6, 1], [4, -3, 3, -4], [-5, 5, 0, -3], [1, -7, 1, 0], [3, 0, 7, -7], [-5, 13, -5, 0], [-2, 2, 0, -11], [8, -7, 7, -8], [-6, -1, -6, 0], [2, 0, -3, 3], [-7, 7, -7, 7], [3, 8, -8, -3], [-3, 3, 0, -4], [0, 6, 1, 6], [8, 0, 4, -4], [0, 3, 2, 3], [-8, -2, -8, 0], [-6, 0, 8, -8], [-7, 11, -7, 0], [8, -8, 0, -1], [3, -7, 3, 0], [0, -8, -5, -8], [0, -16, 10, -16], [-1, -5, 5, 1], [0, -4, 4, 0], [0, 1, 16, 1], [0, -2, -5, -2], [-12, 0, -12, 0], [2, -2, 0, -19], [7, -11, 7, 0], [14, 0, 6, -6], [-5, 0, 2, -2], [14, -15, 15, -14], [0, -13, -6, -13], [-13, 13, 0, 5], [-10, 8, -8, 10], [-10, 22, -22, 10], [0, -5, 14, -5], [8, 0, 15, -15], [-23, 23, -23, 23], [9, -9, 0, -6], [-12, 0, -18, 18], [3, -15, 3, 0], [-11, 11, 0, 13], [2, -15, 15, -2], [10, -19, 10, 0], [0, 8, -7, 8], [0, 0, 0, -11], [7, 0, -10, 10], [0, 0, 9, 0], [7, -14, 7, 0], [19, -10, 10, -19], [-10, 0, -10, 10], [8, -8, 0, 13], [14, 11, 14, 0], [0, 11, -26, 11], [16, 0, -5, 5], [-1, 1, 0, -14], [-24, 24, 0, 6], [30, 0, 9, -9], [26, -16, 26, 0], [-1, -21, 21, 1], [10, -10, 0, 18], [-17, 0, -10, 10], [4, 20, 4, 0], [-8, 14, -14, 8], [4, 0, -16, 16], [0, 2, 2, 2], [-9, 12, -12, 9], [-13, 13, 0, 30], [-5, 0, -1, 1], [0, -5, 0, -5], [-1, 8, -8, 1], [-3, -2, -3, 0], [-9, 0, -17, 17], [19, 0, -2, 2], [-17, -6, -17, 0], [2, 23, 2, 0], [0, 22, -19, 22], [-3, 3, 0, 27], [5, -5, 0, 2], [0, -24, 20, -24], [0, 19, 1, 19], [2, -2, 0, 9], [-9, 11, -9, 0], [-9, 3, -3, 9], [0, 15, 11, 15], [2, -2, 0, -13], [2, 19, -19, -2], [0, 28, -20, 28], [11, 0, 28, -28], [14, -1, 14, 0], [0, 0, 0, -1], [18, 0, 18, -18], [0, 16, 0, 0], [6, -6, 0, 4], [38, -27, 27, -38], [0, -16, -9, -16], [-10, 0, -12, 12], [0, 6, -36, 6], [-24, 24, 0, 21], [0, -14, 23, -14], [-12, -9, -12, 0], [10, 0, 0, -10], [-2, 2, 0, -15], [-25, 0, 4, -4], [-20, 0, 9, -9], [-26, 14, -14, 26], [15, -27, 15, 0], [28, 0, 17, -17], [30, 0, 0, -30], [0, 17, -8, 17], [-13, -1, -13, 0], [16, -16, 0, -23], [28, 0, 25, -25], [8, -8, 0, 40], [-13, 12, -12, 13], [-5, -18, -5, 0], [0, -28, 24, -28], [18, -16, 16, -18], [-30, 2, -2, 30], [-34, 0, 9, -9], [0, -2, 39, -2], [-9, 15, -9, 0], [2, -31, 2, 0], [-17, 22, -17, 0], [0, -24, -16, -24], [48, -48, 0, -21], [6, -22, 22, -6], [16, 6, -6, -16], [21, -21, 0, 14], [0, -22, 17, -22], [-5, -38, -5, 0], [7, 0, -5, 5], [7, 0, -9, 9], [-8, 43, -8, 0], [0, 0, -13, 0], [19, 0, 3, -3], [0, -35, 10, -35], [23, -23, 0, 20], [2, 17, 2, 0], [29, -39, 39, -29], [16, -5, 16, 0], [0, -24, 0, 0], [13, 27, -27, -13], [-26, 11, -26, 0], [16, 0, 6, -6], [-2, 2, 0, -3], [13, 0, 25, -25], [0, 36, -6, 36], [27, -17, 17, -27], [-1, 1, 0, 14], [-25, 0, -15, 15], [-37, 37, 0, 4]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_847_f_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_847_2_f_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_847_2_f_c(:prec:=4)
    chi := MakeCharacter_847_f();
    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_847_2_f_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_847_2_f_c( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_847_f();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![1, -1, 6, 4, 1]>,<3,R![1, -2, 4, -3, 1]>,<13,R![16, -16, 16, -6, 1]>],Snew);
    return Vf;
end function;