
// Make newform 1575.2.a.t in Magma, downloaded from the LMFDB on 25 April 2024.
// To make the character of type GrpDrchElt, type "MakeCharacter_1575_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_1575_2_a_t();".
// 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_1575_2_a_t();".
// 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 := [-3, -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_1575_a();"
function MakeCharacter_1575_a()
    N := 1575;
    order := 1;
    char_gens := [1226, 127, 451];
    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_1575_a_Hecke(Kf)
    return MakeCharacter_1575_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], [0, 0], [0, 0], [-1, 0], [3, 0], [-2, 2], [0, 2], [2, 2], [3, -4], [3, 2], [2, -4], [-5, 4], [0, 0], [-5, -2], [6, 2], [-6, 4], [6, 2], [8, -4], [-11, -2], [3, 0], [4, -2], [-1, -6], [6, -4], [6, -6], [10, -4], [-12, -2], [10, -6], [0, 0], [-7, 4], [3, -6], [1, -6], [12, -2], [6, -4], [-4, 10], [21, -2], [-7, 6], [4, -8], [-8, -4], [6, -10], [6, -6], [0, 0], [8, 2], [12, -4], [1, -4], [3, 6], [8, 0], [8, 8], [-20, 2], [18, 2], [2, -4], [-15, 6], [-24, 4], [14, -2], [0, 6], [6, -12], [-15, 4], [-6, 4], [-22, -2], [10, 0], [15, -6], [-14, 12], [6, 2], [4, 2], [0, -6], [10, 6], [-21, 2], [11, -14], [-2, 4], [21, 4], [-10, 18], [-30, 0], [3, -12], [4, -8], [1, 0], [-1, -6], [6, -14], [15, 6], [-2, 0], [3, 6], [2, -6], [-6, 0], [-1, -4], [-24, 8], [28, 4], [2, 2], [-12, 12], [21, 6], [13, -4], [-6, 14], [-8, -4], [18, -8], [-30, -2], [7, 6], [3, 0], [-28, 0], [-18, 4], [-6, 2], [18, 8], [16, 0], [-13, -8], [25, 2], [-21, 14], [6, 4], [15, -6], [-1, -2], [-26, -2], [24, 6], [0, 12], [-15, 4], [8, 4], [10, 6], [31, 8], [9, 6], [2, -2], [-1, 10], [-9, -6], [-20, -8], [6, 0], [6, -4], [12, 0], [-34, 6], [10, 0], [-18, 4], [9, -12], [32, 4], [30, -4], [2, -16], [-36, 4], [28, -2], [-20, 0], [17, -6], [0, -12], [-28, 12], [-41, 0], [0, 12], [-4, -12], [6, 0], [4, -14], [12, -18], [9, -18], [-22, 16], [6, -24], [-11, -6], [-3, -12], [32, -14], [36, -6], [16, -4], [0, 12], [-22, -12], [33, -12], [22, 0], [-6, -12], [-11, -2], [-24, 4], [4, 4], [-15, 0], [-13, -2], [-12, 14], [-8, 28], [-6, 0], [36, -16], [-9, -2], [4, 16], [6, -26], [21, -10], [-6, 20], [23, 10], [-26, 18], [-13, 28], [12, 2], [21, 4], [2, 6], [9, 8], [22, -8], [20, -14], [24, -2], [35, 6], [-6, 12], [46, 6], [-22, 8], [-17, 6], [-24, -4], [19, 8], [6, -8], [-9, 8], [30, -16], [-11, 12], [-26, -12], [5, 12], [-24, -10], [-14, 0], [3, -16], [-7, 6], [-54, 4], [-3, 12], [-24, 12], [17, -20], [-41, 4], [-6, 26], [-30, 20], [6, -12], [-22, -16], [-2, -8], [-4, 8], [12, 4], [48, -4], [2, 16], [-24, 8], [-3, 26], [20, -20], [-5, -8], [-60, 2], [-5, 10], [0, 28], [-24, 6], [-16, 18], [19, 6], [18, -30], [-9, 28], [21, 14], [-7, 8], [8, 6], [-15, -6], [37, -26], [42, 6], [-22, 0], [24, -14], [-15, 8], [28, -30], [15, -24], [-41, 0], [-34, 0], [20, -28], [57, 2], [10, -22], [-6, -28], [8, 4], [27, 2], [-21, -12], [-24, -12], [-9, -4], [-22, -14], [10, 16], [35, 8], [30, 2], [12, 22], [46, -8], [-42, 24], [-28, 4], [-48, 8], [-50, 12], [24, -24], [-12, -24], [32, -34], [30, -6], [-24, 32], [-31, 4], [-20, 10], [-6, 2], [-26, 10], [28, -8], [-39, 8], [50, 8], [-2, -12], [-24, -2], [-16, -16], [-3, -18], [12, 10], [-29, -2], [57, -10], [-28, 16], [-20, 0], [-56, 16], [-49, -6], [64, 2], [-20, -2], [45, -8], [-10, 12], [35, -28], [0, 34], [0, -18], [-28, 32], [-30, 30], [8, 6], [16, -26], [51, 4], [73, -4], [15, -18], [-28, 8], [42, -32], [21, -30], [-30, 24], [-3, -10], [-12, 42], [61, -12], [-12, 6], [-4, 8], [18, 10], [48, -12], [10, 12], [-32, -6], [-18, -24], [11, 14], [-39, 0], [-13, 10], [-2, 8], [39, -20], [38, 6], [-15, -32], [58, -16], [-36, 6], [6, 24], [27, -18], [4, 8], [-45, -4], [-28, 14], [-18, 28], [12, 0], [4, 16], [39, 6], [32, 18], [-38, -8], [-18, -18], [-35, -14], [-9, 26], [26, 12], [23, -2], [10, -8], [-45, 12], [9, 6], [-22, -4], [-51, 14], [-22, 8], [12, 18], [20, -36], [66, -6], [41, 0], [-42, 18], [14, -6], [-8, 10], [10, -24], [57, 6], [-12, 44], [-13, 26], [-3, -6], [3, 32], [20, 2], [-53, 22], [-54, 2], [-72, 6], [-16, -10], [1, -20], [78, -12], [-14, 18], [11, -16], [42, 6], [-6, 0], [36, -6], [-18, -4], [48, 4], [-35, 20], [-30, 48], [-12, 12], [3, 0], [-2, 30], [-14, 4], [42, 0], [-17, 10], [-49, -16], [27, -48], [-10, 8], [15, -36], [-54, 4], [-10, -20], [-47, 36], [0, -36], [-69, 0], [-32, -2], [30, -26], [40, 6], [24, -6], [15, -14], [1, 10], [63, 6], [-52, 38], [60, -12], [29, -6], [70, -8], [31, 26], [48, -24], [-19, -36], [-6, -8], [51, -12], [-74, 16], [63, -8], [-41, 16], [-28, 4], [42, -2], [-40, 28], [-9, 10], [14, -18], [-45, -6], [25, -14], [30, 14], [30, 6], [2, 26], [37, -28], [78, 4], [40, -48], [42, 0], [-14, 10], [33, -10], [-48, 36], [59, 2], [-5, -24], [-42, 46], [-60, 8], [28, -26], [60, -8], [6, -12], [-18, 0], [16, -30], [24, 32], [0, 32], [-62, 4], [36, -6], [21, -16], [30, -36], [68, -10], [-18, 24]];
    aps := ConvertToHeckeField(raw_aps);
    chi := MakeCharacter_1575_a_Hecke(Universe(aps));
    return ExtendMultiplicatively(weight, aps, chi);
end function;


// To make the newform (type ModFrm), type "MakeNewformModFrm_1575_2_a_t();".
// 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_1575_2_a_t(:prec:=2)
    chi := MakeCharacter_1575_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_1575_2_a_t();".
// 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_1575_2_a_t( : sign := -1)
    R<x> := PolynomialRing(Rationals());
    chi := MakeCharacter_1575_a();
    // SetVerbose("ModularSymbols", true);
    Snew := NewSubspace(CuspidalSubspace(ModularSymbols(chi,2,sign)));
    Vf := Kernel([<2,R![-3, -1, 1]>,<11,R![-3, 1]>,<13,R![-12, 2, 1]>],Snew);
    return Vf;
end function;