
// Make newform 1001.2.a.b in Magma, downloaded from the LMFDB on 17 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1001_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_1001_2_a_b();".
// 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_1001_2_a_b();".
// 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
        Kf := Rationals();
    end if;
    return [Kf!elt[1] : elt in input];
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_1001_a();"
function MakeCharacter_1001_a()
    N := 1001;
    order := 1;
    char_gens := [430, 365, 925];
    v := [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_1001_a_Hecke(Kf)
    return MakeCharacter_1001_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 := [[-1], [0], [-2], [-1], [1], [-1], [-2], [-4], [0], [6], [-4], [6], [6], [12], [4], [-10], [0], [10], [12], [0], [14], [0], [-4], [-14], [-14], [10], [4], [-12], [-2], [18], [-8], [-12], [10], [4], [-2], [0], [14], [12], [-8], [2], [4], [-2], [0], [-22], [-18], [20], [28], [4], [-28], [-10], [18], [0], [-18], [0], [2], [-16], [-10], [8], [22], [-6], [28], [-30], [-28], [20], [-6], [-18], [28], [10], [-4], [-6], [-6], [16], [28], [22], [4], [28], [6], [-10], [34], [-2], [32], [22], [24], [26], [0], [-36], [18], [2], [-22], [24], [-8], [24], [32], [28], [-4], [0], [30], [-30], [-20], [38], [-4], [22], [-36], [18], [36], [-30], [-8], [-42], [16], [22], [16], [22], [-22], [24], [8], [18], [-16], [12], [30], [20], [-34], [-38], [-6], [-4], [-8], [-26], [-26], [36], [28], [26], [4], [-24], [24], [22], [14], [6], [-26], [-52], [-34], [10], [-20], [30], [8], [-28], [-50], [20], [26], [-18], [-32], [-32], [-2], [-22], [20], [32], [36], [8], [32], [50], [46], [-6], [52], [-54], [-48], [32], [-30], [28], [40], [-38], [-6], [30], [-4], [-26], [-8], [-6], [28], [-30], [36], [6], [-32], [-14], [-16], [-20], [38], [-10], [0], [14], [-50], [32], [10], [-48], [-22], [-36], [-4], [54], [-12], [42], [-46], [-18], [6], [0], [38], [32], [38], [38], [40], [-66], [36], [-36], [34], [-8], [58], [-18], [-24], [16], [48], [2], [48], [22], [0], [30], [14], [48], [-30], [-16], [-12], [-34], [18], [0], [32], [-44], [-50], [-60], [-48], [26], [64], [-24], [-30], [30], [-12], [12], [12], [-44], [76], [-34], [30], [72], [-36], [72], [28], [24], [-58], [6], [32], [-54], [-70], [-44], [-10], [-76], [54], [22], [-32], [-4], [50], [2], [-38], [-40], [-18], [42], [20], [30], [-2], [-36], [58], [-56], [38], [-20], [-52], [22], [50], [44], [16], [64], [80], [42], [68], [-40], [2], [-66], [12], [-66], [14], [-24], [74], [-12], [-18], [-54], [-76], [-2], [68], [-36], [-34], [62], [-32], [-36], [-60], [34], [-4], [46], [-72], [-10], [64], [-74], [-54], [-76], [-16], [-18], [32], [-16], [-46], [-6], [-28], [74], [-38], [16], [2], [66], [60], [-40], [48], [-34], [70], [62], [32], [-36], [36], [-72], [94], [-66], [-14], [-24], [38], [42], [26], [40], [-66], [-84], [-50], [20], [-16], [-18], [76], [-38], [-50], [-88], [-10], [-10], [36], [28], [-78], [-40], [-50], [70], [48], [-60], [56], [10], [98], [88], [26], [-68], [8], [-48], [38], [56], [94], [-48], [-32], [14], [30], [-26], [6], [-6], [16], [-54], [28], [-4], [32], [22], [76], [-68], [-62], [-58], [68], [-8], [-8], [-14], [56], [74], [-12], [-90], [-86], [-94], [80], [2], [42], [88], [62], [-6], [-40], [-8], [-58], [62], [-20], [20], [50], [-98], [-64], [28], [26], [8], [78], [2], [-72], [12], [34], [94], [60], [-6], [16], [-32]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1001_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1001_2_a_b();".
// 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_1001_2_a_b(:prec:=1)
    chi := MakeCharacter_1001_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_1001_2_a_b();".
// 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_1001_2_a_b( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1001_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![1, 1]>,<3,R![0, 1]>],Snew);
    return Vf;
end function;