def gf_factor(f, p, K): """ Factor (non square-free) polynomials in ``GF(p)[x]``. Given a possibly non square-free polynomial ``f`` in ``GF(p)[x]``, returns its complete factorization into irreducibles:: f_1(x)**e_1 f_2(x)**e_2 ... f_d(x)**e_d where each ``f_i`` is a monic polynomial and ``gcd(f_i, f_j) == 1``, for ``i != j``. The result is given as a tuple consisting of the leading coefficient of ``f`` and a list of factors of ``f`` with their multiplicities. The algorithm proceeds by first computing square-free decomposition of ``f`` and then iteratively factoring each of square-free factors. Consider a non square-free polynomial ``f = (7*x + 1) (x + 2)**2`` in ``GF(11)[x]``. We obtain its factorization into irreducibles as follows:: >>> from diofant.polys.domains import ZZ >>> gf_factor(ZZ.map([5, 2, 7, 2]), 11, ZZ) (5, [([1, 2], 1), ([1, 8], 2)]) We arrived with factorization ``f = 5 (x + 2) (x + 8)**2``. We didn't recover the exact form of the input polynomial because we requested to get monic factors of ``f`` and its leading coefficient separately. Square-free factors of ``f`` can be factored into irreducibles over ``GF(p)`` using three very different methods: Berlekamp efficient for very small values of ``p`` (usually ``p < 25``) Cantor-Zassenhaus efficient on average input and with "typical" ``p`` Shoup-Kaltofen-Gathen efficient with very large inputs and modulus If you want to use a specific factorization method, instead of the default one, set ``GF_FACTOR_METHOD`` with one of ``berlekamp``, ``zassenhaus`` or ``shoup`` values. References ========== .. [1] [Gathen99]_ """ lc, f = gf_monic(f, p, K) if gf_degree(f) < 1: return lc, [] factors = [] for g, n in gf_sqf_list(f, p, K)[1]: for h in gf_factor_sqf(g, p, K)[1]: factors.append((h, n)) return lc, _sort_factors(factors)
def dup_zz_factor_sqf(f, K): """Factor square-free (non-primitive) polyomials in `Z[x]`. """ cont, g = dup_primitive(f, K) n = dup_degree(g) if dup_LC(g, K) < 0: cont, g = -cont, dup_neg(g, K) if n <= 0: return cont, [] elif n == 1: return cont, [g] if query('USE_IRREDUCIBLE_IN_FACTOR'): if dup_zz_irreducible_p(g, K): return cont, [g] factors = None if query('USE_CYCLOTOMIC_FACTOR'): factors = dup_zz_cyclotomic_factor(g, K) if factors is None: factors = dup_zz_zassenhaus(g, K) return cont, _sort_factors(factors, multiple=False)
def gf_edf_shoup(f, n, p, K): """ Gathen-Shoup: Probabilistic Equal Degree Factorization Given a monic square-free polynomial ``f`` in ``GF(p)[x]`` and integer ``n`` such that ``n`` divides ``deg(f)``, returns all irreducible factors ``f_1,...,f_d`` of ``f``, each of degree ``n``. This is a complete factorization over Galois fields. This algorithm is an improved version of Zassenhaus algorithm for large ``deg(f)`` and modulus ``p`` (especially for ``deg(f) ~ lg(p)``). Examples ======== >>> from diofant.polys.domains import ZZ >>> gf_edf_shoup(ZZ.map([1, 2837, 2277]), 1, 2917, ZZ) [[1, 852], [1, 1985]] References ========== .. [1] [Shoup91]_ .. [2] [Gathen92]_ """ N, q = gf_degree(f), int(p) if not N: return [] if N <= n: return [f] factors, x = [f], [K.one, K.zero] r = gf_random(N - 1, p, K) if p == 2: h = gf_pow_mod(x, q, f, p, K) H = gf_trace_map(r, h, x, n - 1, f, p, K)[1] h1 = gf_gcd(f, H, p, K) h2 = gf_quo(f, h1, p, K) factors = gf_edf_shoup(h1, n, p, K) \ + gf_edf_shoup(h2, n, p, K) else: b = gf_frobenius_monomial_base(f, p, K) H = _gf_trace_map(r, n, f, b, p, K) h = gf_pow_mod(H, (q - 1)//2, f, p, K) h1 = gf_gcd(f, h, p, K) h2 = gf_gcd(f, gf_sub_ground(h, K.one, p, K), p, K) h3 = gf_quo(f, gf_mul(h1, h2, p, K), p, K) factors = gf_edf_shoup(h1, n, p, K) \ + gf_edf_shoup(h2, n, p, K) \ + gf_edf_shoup(h3, n, p, K) return _sort_factors(factors, multiple=False)
def dup_factor_list(f, K0): """Factor polynomials into irreducibles in `K[x]`. """ j, f = dup_terms_gcd(f, K0) cont, f = dup_primitive(f, K0) if K0.is_FiniteField: coeff, factors = dup_gf_factor(f, K0) elif K0.is_Algebraic: coeff, factors = dup_ext_factor(f, K0) else: if not K0.is_Exact: K0_inexact, K0 = K0, K0.get_exact() f = dup_convert(f, K0_inexact, K0) else: K0_inexact = None if K0.has_Field: K = K0.get_ring() denom, f = dup_clear_denoms(f, K0, K) f = dup_convert(f, K0, K) else: K = K0 if K.is_ZZ: coeff, factors = dup_zz_factor(f, K) elif K.is_Poly: f, u = dmp_inject(f, 0, K) coeff, factors = dmp_factor_list(f, u, K.domain) for i, (f, k) in enumerate(factors): factors[i] = (dmp_eject(f, u, K), k) coeff = K.convert(coeff, K.domain) else: # pragma: no cover raise DomainError('factorization not supported over %s' % K0) if K0.has_Field: for i, (f, k) in enumerate(factors): factors[i] = (dup_convert(f, K, K0), k) coeff = K0.convert(coeff, K) if K0_inexact is None: coeff = coeff / denom else: for i, (f, k) in enumerate(factors): f = dup_quo_ground(f, denom, K0) f = dup_convert(f, K0, K0_inexact) factors[i] = (f, k) coeff = K0_inexact.convert(coeff * denom**i, K0) K0 = K0_inexact if j: factors.insert(0, ([K0.one, K0.zero], j)) return coeff * cont, _sort_factors(factors)
def gf_berlekamp(f, p, K): """ Factor a square-free ``f`` in ``GF(p)[x]`` for small ``p``. Examples ======== >>> from diofant.polys.domains import ZZ >>> gf_berlekamp([1, 0, 0, 0, 1], 5, ZZ) [[1, 0, 2], [1, 0, 3]] """ Q = gf_Qmatrix(f, p, K) V = gf_Qbasis(Q, p, K) for i, v in enumerate(V): V[i] = gf_strip(list(reversed(v))) factors = [f] for k in range(1, len(V)): for f in list(factors): s = K.zero while s < p: g = gf_sub_ground(V[k], s, p, K) h = gf_gcd(f, g, p, K) if h != [K.one] and h != f: factors.remove(f) f = gf_quo(f, h, p, K) factors.extend([f, h]) if len(factors) == len(V): return _sort_factors(factors, multiple=False) s += K.one return _sort_factors(factors, multiple=False)
def gf_edf_zassenhaus(f, n, p, K): """ Cantor-Zassenhaus: Probabilistic Equal Degree Factorization Given a monic square-free polynomial ``f`` in ``GF(p)[x]`` and an integer ``n``, such that ``n`` divides ``deg(f)``, returns all irreducible factors ``f_1,...,f_d`` of ``f``, each of degree ``n``. EDF procedure gives complete factorization over Galois fields. Consider the square-free polynomial ``f = x**3 + x**2 + x + 1`` in ``GF(5)[x]``. Let's compute its irreducible factors of degree one:: >>> from diofant.polys.domains import ZZ >>> gf_edf_zassenhaus([1,1,1,1], 1, 5, ZZ) [[1, 1], [1, 2], [1, 3]] References ========== .. [1] [Gathen99]_ .. [2] [Geddes92]_ """ factors, q = [f], int(p) if gf_degree(f) <= n: return factors N = gf_degree(f) // n if p != 2: b = gf_frobenius_monomial_base(f, p, K) while len(factors) < N: r = gf_random(2*n - 1, p, K) if p == 2: h = r for i in range(0, 2**(n*N - 1)): r = gf_pow_mod(r, 2, f, p, K) h = gf_add(h, r, p, K) g = gf_gcd(f, h, p, K) else: h = _gf_pow_pnm1d2(r, n, f, b, p, K) g = gf_gcd(f, gf_sub_ground(h, K.one, p, K), p, K) if g != [K.one] and g != f: factors = gf_edf_zassenhaus(g, n, p, K) \ + gf_edf_zassenhaus(gf_quo(f, g, p, K), n, p, K) return _sort_factors(factors, multiple=False)
def test__sort_factors(): assert _sort_factors([], multiple=True) == [] assert _sort_factors([], multiple=False) == [] F = [[1, 2, 3], [1, 2], [1]] G = [[1], [1, 2], [1, 2, 3]] assert _sort_factors(F, multiple=False) == G F = [[1, 2], [1, 2, 3], [1, 2], [1]] G = [[1], [1, 2], [1, 2], [1, 2, 3]] assert _sort_factors(F, multiple=False) == G F = [[2, 2], [1, 2, 3], [1, 2], [1]] G = [[1], [1, 2], [2, 2], [1, 2, 3]] assert _sort_factors(F, multiple=False) == G F = [([1, 2, 3], 1), ([1, 2], 1), ([1], 1)] G = [([1], 1), ([1, 2], 1), ([1, 2, 3], 1)] assert _sort_factors(F, multiple=True) == G F = [([1, 2], 1), ([1, 2, 3], 1), ([1, 2], 1), ([1], 1)] G = [([1], 1), ([1, 2], 1), ([1, 2], 1), ([1, 2, 3], 1)] assert _sort_factors(F, multiple=True) == G F = [([2, 2], 1), ([1, 2, 3], 1), ([1, 2], 1), ([1], 1)] G = [([1], 1), ([1, 2], 1), ([2, 2], 1), ([1, 2, 3], 1)] assert _sort_factors(F, multiple=True) == G F = [([2, 2], 1), ([1, 2, 3], 1), ([1, 2], 2), ([1], 1)] G = [([1], 1), ([2, 2], 1), ([1, 2], 2), ([1, 2, 3], 1)] assert _sort_factors(F, multiple=True) == G
def dmp_trial_division(f, factors, u, K): """Determine multiplicities of factors using trial division. """ result = [] for factor in factors: k = 0 while True: q, r = dmp_div(f, factor, u, K) if dmp_zero_p(r, u): f, k = q, k + 1 else: break result.append((factor, k)) return _sort_factors(result)
def gf_shoup(f, p, K): """ Factor a square-free ``f`` in ``GF(p)[x]`` for large ``p``. Examples ======== >>> from diofant.polys.domains import ZZ >>> gf_shoup(ZZ.map([1, 4, 3]), 5, ZZ) [[1, 1], [1, 3]] """ factors = [] for factor, n in gf_ddf_shoup(f, p, K): factors += gf_edf_shoup(factor, n, p, K) return _sort_factors(factors, multiple=False)
def dmp_zz_factor(f, u, K): """ Factor (non square-free) polynomials in `Z[X]`. Given a multivariate polynomial `f` in `Z[x]` computes its complete factorization `f_1, ..., f_n` into irreducibles over integers:: f = content(f) f_1**k_1 ... f_n**k_n The factorization is computed by reducing the input polynomial into a primitive square-free polynomial and factoring it using Enhanced Extended Zassenhaus (EEZ) algorithm. Trial division is used to recover the multiplicities of factors. The result is returned as a tuple consisting of:: (content(f), [(f_1, k_1), ..., (f_n, k_n)) Consider polynomial `f = 2*(x**2 - y**2)`:: >>> from diofant.polys import ring, ZZ >>> R, x,y = ring("x,y", ZZ) >>> R.dmp_zz_factor(2*x**2 - 2*y**2) (2, [(x - y, 1), (x + y, 1)]) In result we got the following factorization:: f = 2 (x - y) (x + y) References ========== .. [1] [Gathen99]_ """ if not u: return dup_zz_factor(f, K) if dmp_zero_p(f, u): return K.zero, [] cont, g = dmp_ground_primitive(f, u, K) if dmp_ground_LC(g, u, K) < 0: cont, g = -cont, dmp_neg(g, u, K) if all(d <= 0 for d in dmp_degree_list(g, u)): return cont, [] G, g = dmp_primitive(g, u, K) factors = [] if dmp_degree(g, u) > 0: g = dmp_sqf_part(g, u, K) H = dmp_zz_wang(g, u, K) factors = dmp_trial_division(f, H, u, K) for g, k in dmp_zz_factor(G, u - 1, K)[1]: factors.insert(0, ([g], k)) return cont, _sort_factors(factors)
def dmp_factor_list(f, u, K0): """Factor polynomials into irreducibles in `K[X]`. """ if not u: return dup_factor_list(f, K0) J, f = dmp_terms_gcd(f, u, K0) cont, f = dmp_ground_primitive(f, u, K0) if K0.is_FiniteField: # pragma: no cover coeff, factors = dmp_gf_factor(f, u, K0) elif K0.is_Algebraic: coeff, factors = dmp_ext_factor(f, u, K0) else: if not K0.is_Exact: K0_inexact, K0 = K0, K0.get_exact() f = dmp_convert(f, u, K0_inexact, K0) else: K0_inexact = None if K0.has_Field: K = K0.get_ring() denom, f = dmp_clear_denoms(f, u, K0, K) f = dmp_convert(f, u, K0, K) else: K = K0 if K.is_ZZ: levels, f, v = dmp_exclude(f, u, K) coeff, factors = dmp_zz_factor(f, v, K) for i, (f, k) in enumerate(factors): factors[i] = (dmp_include(f, levels, v, K), k) elif K.is_Poly: f, v = dmp_inject(f, u, K) coeff, factors = dmp_factor_list(f, v, K.domain) for i, (f, k) in enumerate(factors): factors[i] = (dmp_eject(f, v, K), k) coeff = K.convert(coeff, K.domain) else: # pragma: no cover raise DomainError('factorization not supported over %s' % K0) if K0.has_Field: for i, (f, k) in enumerate(factors): factors[i] = (dmp_convert(f, u, K, K0), k) coeff = K0.convert(coeff, K) if K0_inexact is None: coeff = coeff / denom else: for i, (f, k) in enumerate(factors): f = dmp_quo_ground(f, denom, u, K0) f = dmp_convert(f, u, K0, K0_inexact) factors[i] = (f, k) coeff = K0_inexact.convert(coeff * denom**i, K0) K0 = K0_inexact for i, j in enumerate(reversed(J)): if not j: continue term = {(0, ) * (u - i) + (1, ) + (0, ) * i: K0.one} factors.insert(0, (dmp_from_dict(term, u, K0), j)) return coeff * cont, _sort_factors(factors)