
// Make newform 1248.2.a.f in Magma, downloaded from the LMFDB on 24 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1248_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_1248_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_1248_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
        Kf := Rationals();
    end if;
    return [Kf!elt[1] : elt in input];
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_1248_a();"
function MakeCharacter_1248_a()
    N := 1248;
    order := 1;
    char_gens := [703, 1093, 833, 769];
    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_1248_a_Hecke(Kf)
    return MakeCharacter_1248_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], [1], [-2], [0], [-4], [1], [-6], [8], [-8], [2], [-8], [-10], [6], [4], [0], [-14], [12], [-10], [8], [0], [-14], [4], [-4], [-10], [10], [10], [4], [-12], [14], [-6], [4], [12], [-10], [4], [6], [8], [-10], [-16], [16], [10], [-4], [-10], [-24], [18], [6], [-4], [-12], [0], [-12], [6], [18], [0], [10], [4], [-22], [24], [2], [0], [-26], [-18], [20], [14], [16], [-16], [-22], [30], [32], [2], [20], [14], [6], [-8], [28], [-18], [-32], [8], [-6], [-34], [6], [-30], [4], [6], [0], [2], [4], [28], [-10], [2], [6], [-16], [-36], [-24], [-32], [-20], [-40], [16], [-18], [-22], [-4], [-2], [-28], [-2], [-12], [-6], [20], [-14], [-4], [-34], [0], [42], [-44], [-26], [14], [-24], [-8], [-38], [-32], [-32], [26], [20], [22], [-14], [-22], [-4], [-32], [-22], [6], [0], [4], [-2], [16], [24], [20], [38], [38], [2], [-18], [8], [18], [-22], [-16], [-18], [-52], [-12], [-34], [-16], [-42], [-54], [4], [-24], [14], [10], [52], [32], [-20], [8], [12], [30], [-38], [14], [20], [-6], [8], [-12], [-26], [24], [44], [14], [-6], [-46], [20], [30], [32], [34], [-44], [42], [-8], [38], [-12], [-10], [40], [-44], [22], [6], [-8], [-22], [-18], [-64], [-14], [24], [-30], [-20], [60], [30], [-4], [-14], [66], [-66], [14], [16], [54], [-60], [54], [-46], [-28], [42], [32], [52], [54], [-4], [18], [-22], [4], [52], [-24], [-22], [4], [42], [24], [14], [-42], [-40], [-26], [-16], [44], [-34], [-6], [-56], [60], [-4], [46], [20], [40], [42], [12], [72], [-6], [-42], [12], [-72], [-4], [52], [-4], [78], [-66], [24], [72], [36], [8], [-24], [-2], [6], [-32], [-22], [18], [-20], [-58], [-24], [2], [-38], [4], [-60], [-26], [54], [6], [20], [-26], [30], [-48], [82], [22], [-40], [-30], [4], [2], [-32], [-20], [30], [-38], [4], [16], [72], [-24], [-26], [-80], [-64], [-30], [-10], [-8], [42], [18], [-12], [-42], [-68], [38], [66], [4], [-14], [-76], [40], [-6], [-42], [-12], [36], [60], [-70], [-36], [-50], [48], [46], [32], [38], [-14], [44], [-48], [-38], [44], [32], [10], [-62], [36], [-54], [74], [-32], [14], [-14], [-16], [-8], [-64], [-78], [-50], [-54], [60], [-4], [40], [-76], [46], [22], [-78], [76], [-26], [-6], [-50], [-28], [-66], [4], [38], [0], [-48], [18], [-16], [-62], [86], [-28], [-50], [50], [-24], [20], [18], [0], [22], [-6], [0], [76], [-44], [10], [14], [56], [10], [84], [-28], [72], [34], [76], [62], [60], [48], [-46], [-22], [-54], [-34], [-26], [64], [-66], [96], [24], [0], [22], [24], [-8], [90], [70], [36], [-20], [0], [26], [-88], [2], [-60], [30], [-82], [10], [64], [78], [-42], [-100], [-18], [6], [-40], [20], [34], [26], [-12], [28], [10], [90], [32], [60], [-42], [-24], [42], [-58], [32], [76], [26], [-58], [-20], [-74], [-8], [-40]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1248_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1248_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_1248_2_a_f(:prec:=1)
    chi := MakeCharacter_1248_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_1248_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_1248_2_a_f( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1248_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<5,R![2, 1]>,<7,R![0, 1]>,<11,R![4, 1]>],Snew);
    return Vf;
end function;