
// Make newform 847.2.f.m in Magma, downloaded from the LMFDB on 24 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_m();".
// 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_m();".
// 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 := [[1, 1, -1, -1], [0, -2, 2, -2], [0, 2, 0, 0], [0, 0, 0, 1], [0, 0, 0, 0], [2, 0, 0, -2], [-2, 0, -2, 0], [0, -4, 0, -4], [0, 0, 4, -4], [-4, 4, 0, 6], [4, -6, 6, -4], [-4, 4, 0, 6], [0, 2, 8, 2], [-8, 0, 0, 0], [0, -2, 6, -2], [-2, 6, -6, 2], [-2, 2, 0, 0], [-2, -4, -2, 0], [12, 0, 4, -4], [4, 4, 4, 0], [-2, 2, 0, -2], [-4, -4, 4, 4], [-12, 8, -12, 0], [2, 0, 0, 0], [-10, -2, 2, 10], [-6, 8, -8, 6], [6, -6, 0, -4], [0, 0, 4, 0], [2, 0, 4, -4], [0, 0, 2, 0], [-8, 16, -8, 0], [-12, 0, -16, 16], [-4, -10, -4, 0], [-4, 4, 0, -4], [0, 14, 0, 0], [0, -8, 4, -8], [0, 8, -2, 8], [-4, 16, -16, 4], [0, 8, -8, 0], [0, -2, 16, -2], [0, -8, 4, -8], [12, 6, 12, 0], [8, -8, 0, 8], [16, -14, 16, 0], [2, 0, 0, 0], [4, 0, -10, 10], [-4, -12, 12, 4], [0, -10, 6, -10], [-16, 16, 0, -4], [2, 2, -2, -2], [2, 10, -10, -2], [0, 16, -16, 16], [2, 0, 18, -18], [-8, 14, -14, 8], [0, 0, 0, 6], [0, 0, 0, 0], [-12, 6, -12, 0], [4, -4, 0, -8], [-10, -6, 6, 10], [4, -10, 4, 0], [0, -16, -4, -16], [18, -18, 0, -14], [4, 0, 8, -8], [0, 6, -18, 6], [-8, -2, -8, 0], [-14, 14, -14, 14], [-4, 0, -16, 16], [-4, 4, 0, -14], [8, 8, 8, 0], [0, 2, 4, 2], [10, 0, 16, -16], [8, -8, 0, -20], [-18, 18, 0, 12], [-6, 0, 0, 0], [-28, 8, -28, 0], [-4, 18, -18, 4], [16, -16, 0, -6], [-26, 0, -16, 16], [-8, -10, -8, 0], [-2, 20, -20, 2], [16, 0, 14, -14], [0, 20, -10, 20], [12, -12, 12, -12], [-4, 4, 0, 6], [-8, 0, -4, 4], [0, -8, -12, -8], [26, -22, 22, -26], [-24, 10, -24, 0], [6, 0, 10, -10], [-8, 0, 4, -4], [-26, 18, -26, 0], [-4, 20, -4, 0], [0, -20, -4, -20], [0, 0, 0, 0], [-4, 4, 0, -4], [0, -12, -4, -12], [0, 4, 34, 4], [20, -20, 0, -18], [0, 44, 0, 0], [6, 18, -18, -6], [0, 0, -28, 0], [8, -8, 0, -34], [20, -32, 32, -20], [0, 4, -14, 4], [20, 0, -8, 8], [-4, 26, -4, 0], [18, -18, 0, -16], [42, 0, 6, -6], [12, 4, 12, 0], [18, -18, 0, -26], [8, 0, 0, -8], [0, -28, 30, -28], [14, 0, -12, 12], [0, 18, -18, 18], [0, 0, 0, 24], [0, 4, -22, 4], [-18, 18, -18, 0], [-20, -6, 6, 20], [-8, 8, 0, -30], [8, 0, 16, -16], [-26, 0, -24, 24], [-14, 2, -2, 14], [-6, 0, -6, 0], [4, 0, -16, 16], [0, -30, 30, 0], [0, -4, 22, -4], [8, 2, 8, 0], [-38, 38, 0, 28], [4, 0, 34, -34], [2, -2, 0, 10], [20, -12, 12, -20], [16, -24, 16, 0], [0, -4, 36, -4], [-6, -10, 10, 6], [-18, -4, 4, 18], [-22, 0, 6, -6], [0, -20, -6, -20], [-12, -24, -12, 0], [8, 2, 8, 0], [-8, 34, -8, 0], [0, 24, -4, 24], [-24, 24, 0, 30], [24, -40, 40, -24], [-8, 0, 0, 8], [24, -24, 0, -22], [0, 26, 2, 26], [-14, -8, -14, 0], [-14, 0, -2, 2], [-8, 0, -30, 30], [-8, 16, -8, 0], [0, 12, -34, 12], [10, 0, -12, 12], [0, -8, 4, -8], [20, -20, 0, 8], [-4, -16, -4, 0], [-40, 36, -36, 40], [16, 16, 16, 0], [36, -6, 36, 0], [-2, -12, 12, 2], [22, -28, 22, 0], [-20, 0, 24, -24], [-8, 8, 0, 18], [4, 0, 16, -16], [0, 18, -18, 18], [-18, 10, -10, 18], [-10, 10, 0, -28], [32, 0, 36, -36], [14, -14, 0, 10]];
    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_m();".
// 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_m(: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_m();".
// 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_m( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_847_f();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![25, -25, 15, -5, 1]>,<3,R![16, 16, 16, 6, 1]>,<13,R![16, -16, 16, -6, 1]>],Snew);
    return Vf;
end function;