
// Make newform 5850.2.a.c in Magma, downloaded from the LMFDB on 17 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_5850_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_5850_2_a_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_5850_2_a_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
        Kf := Rationals();
    end if;
    return [Kf!elt[1] : elt in input];
end function;


// To make the character of type GrpDrchElt, type "MakeCharacter_5850_a();"
function MakeCharacter_5850_a()
    N := 5850;
    order := 1;
    char_gens := [3251, 3277, 2251];
    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_5850_a_Hecke(Kf)
    return MakeCharacter_5850_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], [0], [-4], [0], [1], [-2], [4], [8], [-2], [-8], [-2], [6], [-12], [0], [10], [0], [-10], [4], [16], [6], [-8], [-4], [14], [6], [-10], [4], [-12], [14], [-10], [12], [-8], [6], [-20], [-10], [-8], [-18], [20], [16], [2], [-16], [-2], [-8], [-18], [-6], [-8], [-12], [-12], [-12], [14], [-26], [-24], [2], [0], [22], [24], [14], [-32], [-18], [-18], [-20], [-6], [12], [0], [-18], [-14], [-20], [22], [-4], [14], [-26], [-24], [-4], [22], [20], [-16], [14], [-10], [-26], [10], [24], [30], [0], [-10], [40], [-36], [6], [-18], [-2], [-20], [-36], [-8], [20], [0], [-44], [16], [38], [-2], [-20], [-2], [-36], [18], [36], [30], [36], [22], [-12], [14], [-40], [10], [-28], [-34], [-2], [-28], [0], [30], [-28], [-48], [18], [-24], [-10], [38], [26], [36], [20], [-18], [-34], [-16], [-52], [22], [4], [-40], [-8], [-50], [-18], [2], [10], [-44], [-46], [-10], [4], [-2], [44], [-36], [38], [8], [14], [-10], [-36], [-24], [-18], [6], [36], [8], [-28], [32], [16], [-26], [6], [30], [52], [30], [28], [48], [38], [56], [-32], [22], [34], [-6], [0], [38], [56], [-26], [-56], [30], [20], [-58], [12], [30], [44], [8], [30], [-42], [16], [30], [-50], [20], [42], [-40], [-10], [12], [-28], [-50], [-52], [14], [2], [-2], [-18], [64], [46], [40], [-58], [18], [0], [34], [-24], [4], [-34], [-28], [-26], [46], [4], [12], [48], [-38], [28], [54], [-24], [2], [38], [24], [-34], [44], [-36], [22], [-34], [16], [28], [16], [14], [-12], [-64], [-66], [12], [-8], [34], [42], [24], [0], [-12], [-12], [-52], [46], [54], [16], [68], [-40], [-20], [-32], [-10], [62], [-48], [-38], [18], [0], [-2], [-20], [-38], [38], [-68], [-12], [-66], [-10], [-2], [-36], [30], [-42], [-52], [26], [46], [-68], [-58], [24], [-26], [-20], [-4], [-18], [26], [8], [-32], [56], [-16], [14], [68], [-72], [-66], [-54], [72], [-2], [54], [28], [78], [48], [-42], [-42], [8], [42], [-8], [-20], [-2], [18], [32], [-36], [4], [6], [-12], [-34], [-48], [38], [-48], [-66], [-26], [-4], [-40], [-38], [8], [-40], [14], [30], [-4], [-58], [30], [76], [78], [2], [44], [20], [40], [42], [-90], [66], [8], [28], [-44], [-60], [70], [-42], [58], [-52], [-58], [-10], [62], [8], [-46], [-64], [38], [4], [24], [-54], [-20], [30], [-26], [12], [-66], [86], [48], [-80], [86], [48], [22], [86], [-72], [-48], [-76], [38], [34], [-4], [-38], [-48], [92], [-64], [6], [-24], [38], [-72], [48], [-58], [-90], [-10], [62], [-90], [-20], [38], [-4], [48], [-56], [-50], [-28], [32], [66], [-6], [16], [20], [24], [-26], [-16], [54], [20], [86], [86], [70], [4], [6], [30], [-48], [22], [6], [-44], [0], [-50], [90], [-12], [60], [62], [62], [32], [-28], [-98], [-40], [6], [-74], [80], [-16], [6], [18], [76], [-58], [-84], [-72]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_5850_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_5850_2_a_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_5850_2_a_c(:prec:=1)
    chi := MakeCharacter_5850_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_5850_2_a_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_5850_2_a_c( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_5850_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<7,R![4, 1]>,<11,R![0, 1]>,<17,R![2, 1]>,<23,R![-8, 1]>,<31,R![8, 1]>],Snew);
    return Vf;
end function;