def dup_primitive(f, K):
"""
Compute content and the primitive form of ``f`` in ``K[x]``.
Examples
========
>>> from diofant.polys import ring, ZZ, QQ
>>> R, x = ring("x", ZZ)
>>> f = 6*x**2 + 8*x + 12
>>> R.dup_primitive(f)
(2, 3*x**2 + 4*x + 6)
>>> R, x = ring("x", QQ)
>>> f = 6*x**2 + 8*x + 12
>>> R.dup_primitive(f)
(2, 3*x**2 + 4*x + 6)
"""
if not f:
return K.zero, f
cont = dup_content(f, K)
if K.is_one(cont):
return cont, f
else:
return cont, dup_quo_ground(f, cont, K)
def dup_half_gcdex(f, g, K):
"""
Half extended Euclidean algorithm in `F[x]`.
Returns ``(s, h)`` such that ``h = gcd(f, g)`` and ``s*f = h (mod g)``.
Examples
========
>>> from diofant.polys import ring, QQ
>>> R, x = ring("x", QQ)
>>> f = x**4 - 2*x**3 - 6*x**2 + 12*x + 15
>>> g = x**3 + x**2 - 4*x - 4
>>> R.dup_half_gcdex(f, g)
(-1/5*x + 3/5, x + 1)
"""
if not K.has_Field:
raise DomainError("can't compute half extended GCD over %s" % K)
a, b = [K.one], []
while g:
q, r = dup_div(f, g, K)
f, g = g, r
a, b = b, dup_sub_mul(a, q, b, K)
a = dup_quo_ground(a, dup_LC(f, K), K)
f = dup_monic(f, K)
return a, f
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 dup_extract(f, g, K):
"""
Extract common content from a pair of polynomials in ``K[x]``.
Examples
========
>>> from diofant.polys import ring, ZZ
>>> R, x = ring("x", ZZ)
>>> R.dup_extract(6*x**2 + 12*x + 18, 4*x**2 + 8*x + 12)
(2, 3*x**2 + 6*x + 9, 2*x**2 + 4*x + 6)
"""
fc = dup_content(f, K)
gc = dup_content(g, K)
gcd = K.gcd(fc, gc)
if not K.is_one(gcd):
f = dup_quo_ground(f, gcd, K)
g = dup_quo_ground(g, gcd, K)
return gcd, f, g
def test_dup_quo_ground():
pytest.raises(ZeroDivisionError,
lambda: dup_quo_ground(dup_normal([1, 2, 3], ZZ), ZZ(0), ZZ))
f = dup_normal([], ZZ)
assert dup_quo_ground(f, ZZ(3), ZZ) == dup_normal([], ZZ)
f = dup_normal([6, 2, 8], ZZ)
assert dup_quo_ground(f, ZZ(1), ZZ) == f
assert dup_quo_ground(f, ZZ(2), ZZ) == dup_normal([3, 1, 4], ZZ)
assert dup_quo_ground(f, ZZ(3), ZZ) == dup_normal([2, 0, 2], ZZ)
f = dup_normal([6, 2, 8], QQ)
assert dup_quo_ground(f, QQ(1), QQ) == f
assert dup_quo_ground(f, QQ(2), QQ) == [QQ(3), QQ(1), QQ(4)]
assert dup_quo_ground(f, QQ(7), QQ) == [QQ(6, 7), QQ(2, 7), QQ(8, 7)]
def dup_inner_subresultants(f, g, K):
"""
Subresultant PRS algorithm in `K[x]`.
Computes the subresultant polynomial remainder sequence (PRS)
and the non-zero scalar subresultants of `f` and `g`.
By [1] Thm. 3, these are the constants '-c' (- to optimize
computation of sign).
The first subdeterminant is set to 1 by convention to match
the polynomial and the scalar subdeterminants.
If 'deg(f) < deg(g)', the subresultants of '(g,f)' are computed.
Examples
========
>>> from diofant.polys import ring, ZZ
>>> R, x = ring("x", ZZ)
>>> R.dup_inner_subresultants(x**2 + 1, x**2 - 1)
([x**2 + 1, x**2 - 1, -2], [1, 1, 4])
References
==========
.. [1] W.S. Brown, The Subresultant PRS Algorithm.
ACM Transaction of Mathematical Software 4 (1978) 237-249
"""
n = dup_degree(f)
m = dup_degree(g)
if n < m:
f, g = g, f
n, m = m, n
if not f:
return [], []
if not g:
return [f], [K.one]
R = [f, g]
d = n - m
b = (-K.one)**(d + 1)
h = dup_prem(f, g, K)
h = dup_mul_ground(h, b, K)
lc = dup_LC(g, K)
c = lc**d
# Conventional first scalar subdeterminant is 1
S = [K.one, c]
c = -c
while h:
k = dup_degree(h)
R.append(h)
f, g, m, d = g, h, k, m - k
b = -lc * c**d
h = dup_prem(f, g, K)
h = dup_quo_ground(h, b, K)
lc = dup_LC(g, K)
if d > 1: # abnormal case
q = c**(d - 1)
c = K.quo((-lc)**d, q)
else:
c = -lc
S.append(-c)
return R, S