def multi_hensel_lift(p, f, f_list, l):
"""Multifactor Hensel lifting.
Input: an integer p, an univariate integer polynomial f such that
f's leading coefficient lc(f) is a unit mod p. Monic polynomials
f_i that are pair-wise coprime mod p satisfying
f = lc(f)*f_1*...*f_r mod p
and an integer l.
Output: monic polynomials ff_1, ..., ff_r satisfying
f = lc(f)*ff_1*...*ff_r mod p**l
ff_i = f_i mod p
"""
r = len(f_list)
lc = f[f.degree]
if r == 1:
lc_g, lc_s, lc_t = modint.xgcd(lc, p**l)
return [f.scale(lc_s).mod_int(p**l, symmetric=True)]
k = int(r/2)
d = int(math.ceil(math.log(l, 2)))
# Divide and conquer the factors.
IntModpPoly = gfpoly.GFPolyFactory(p)
g = IntModpPoly.from_int_dict({0:lc})
for f_i in f_list[0:k]:
g *= IntModpPoly.from_int_dict(f_i.coeffs)
h = IntModpPoly.from_int_dict(f_list[k].coeffs)
for f_i in f_list[k+1:]:
h *= IntModpPoly.from_int_dict(f_i.coeffs)
x, s, t = gfpoly.xgcd(g, h)
g = IntPoly(g.to_sym_int_dict())
h = IntPoly(h.to_sym_int_dict())
s = IntPoly(s.to_sym_int_dict())
t = IntPoly(t.to_sym_int_dict())
# Lift the two coprime parts.
m = p
for j in range(1, d+1):
g, h, s, t = hensel_step(m, f, g, h, s, t)
m *= m
# Call recursively.
return multi_hensel_lift(p, g, f_list[0:k], l) \
+ multi_hensel_lift(p, h, f_list[k:], l)
def test_GFPoly():
from sympy.polynomials.fast import gfpoly
p = 5
IntMod5Poly = gfpoly.GFPolyFactory(p)
IntMod5 = IntMod5Poly.coeff_type
f = IntMod5Poly.from_int_dict({2: 1, 0: 1})
g = IntMod5Poly.from_int_dict({3: 2, 1: 1, 0: 2})
assert f[0] == IntMod5(1)
assert f[1] == IntMod5(0)
assert +f == f
assert -f == IntMod5Poly.from_int_dict({2: -1, 0: -1})
assert f.scale(IntMod5(2), 3) == IntMod5Poly.from_int_dict({5: 2, 3: 2})
assert f + g == IntMod5Poly.from_int_dict({3: 2, 2: 1, 1: 1, 0: 3})
assert f - g == IntMod5Poly.from_int_dict({3: -2, 2: 1, 1: -1, 0: -1})
assert f * g == IntMod5Poly.from_int_dict({5: 2, 3: 3, 2: 2, 1: 1, 0: 2})
assert f**5 == IntMod5Poly.from_int_dict({10: 1, 0: 1})
assert (f * g).diff() == IntMod5Poly.from_int_dict({2: 4, 1: 4, 0: 1})
assert g.monic() \
== (IntMod5(2), IntMod5Poly.from_int_dict({3:1, 1:-2, 0:1}))
assert g.monic()[1].to_sym_int_dict() == {3: 1, 1: -2, 0: 1}
q, r = gfpoly.div(f, g)
assert (not q) and (r == f)
q, r = gfpoly.div(g, f)
assert q == IntMod5Poly.from_int_dict({1: 2})
assert r == IntMod5Poly.from_int_dict({1: 4, 0: 2})
assert gfpoly.gcd(f, g) == IntMod5Poly.from_int_dict({1: 1, 0: 3})
assert gfpoly.gcd(f**3, f**4) == f**3
h, s, t = gfpoly.xgcd(f, g)
assert h == IntMod5Poly.from_int_dict({1: 1, 0: 3})
assert s == IntMod5Poly.from_int_dict({1: 2})
assert t == IntMod5Poly.from_int_dict({0: 4})
assert h == (s * f + t * g)
assert gfpoly.truncate(f, 5) == f
assert gfpoly.truncate(f, 1) == IntMod5Poly.from_int_dict({0: 1})
assert gfpoly.pow_mod(f, 3, IntMod5Poly.from_int_dict({2:1})) \
== gfpoly.truncate(f**3, 2)
p = 3
IntMod3Poly = gfpoly.GFPolyFactory(p)
f = IntMod3Poly.from_int_dict({1:1}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2})
a = gfpoly.distinct_degree_factor(f)
assert [g.to_sym_int_dict() for g in a] \
== [{1: 1, 2: 1}, {0: -1, 1: 1, 3: 1, 4: 1}]
b = gfpoly.equal_degree_factor(a[0], 1)
assert sorted([g.to_sym_int_dict() for g in b]) \
== sorted([{1:1}, {1:1, 0:1}])
c = gfpoly.equal_degree_factor(a[1], 2)
assert sorted([g.to_sym_int_dict() for g in c]) \
== sorted([{2:1, 0:1}, {2:1, 1:1, 0:-1}])
r = gfpoly.factor_sqf(f)
assert r[0] == IntMod3Poly.coeff_type(1)
r = r[1:]
assert len(r) == 4
assert IntMod3Poly.from_int_dict({1: 1}) in r
assert IntMod3Poly.from_int_dict({1: 1, 0: 1}) in r
assert IntMod3Poly.from_int_dict({2: 1, 0: 1}) in r
assert IntMod3Poly.from_int_dict({2: 1, 1: 1, 0: 2}) in r
f = IntMod3Poly.from_int_dict({1:1}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({1:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 0:1}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2}) \
* IntMod3Poly.from_int_dict({2:1, 1:1, 0:2})
r = gfpoly.factor(f)
assert r[0] == IntMod3Poly.coeff_type(1)
test_dict = {}
for item in r[1:]:
test_dict[item[1]] = item[0].to_sym_int_dict()
assert test_dict == {
1: {
1: 1
},
3: {
2: 1,
0: 1
},
6: {
1: 1,
0: 1
},
7: {
2: 1,
1: 1,
0: -1
}
}
