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euclidtools.py
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euclidtools.py
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"""Euclidean algorithms, GCDs, LCMs and polynomial remainder sequences. """
from sympy.polys.densebasic import (
dup_strip, dmp_raise,
dmp_zero, dmp_one, dmp_ground,
dmp_one_p, dmp_zero_p,
dmp_zeros,
dup_degree, dmp_degree, dmp_degree_in,
dup_LC, dmp_LC, dmp_ground_LC,
dmp_multi_deflate, dmp_inflate,
dup_convert, dmp_convert,
dmp_apply_pairs)
from sympy.polys.densearith import (
dup_sub_mul,
dup_neg, dmp_neg,
dup_add, dmp_add,
dup_sub, dmp_sub,
dup_mul, dmp_mul,
dup_pow, dmp_pow,
dup_div, dmp_div,
dup_rem, dmp_rem,
dup_quo, dmp_quo,
dup_prem, dmp_prem,
dup_mul_ground, dmp_mul_ground,
dup_mul_term, dmp_mul_term,
dup_quo_ground, dmp_quo_ground,
dup_max_norm, dmp_max_norm)
from sympy.polys.densetools import (
dup_clear_denoms, dmp_clear_denoms,
dup_diff, dmp_diff,
dup_eval, dmp_eval, dmp_eval_in,
dup_trunc, dmp_ground_trunc,
dup_monic, dmp_ground_monic,
dup_primitive, dmp_ground_primitive,
dup_extract, dmp_ground_extract)
from sympy.polys.galoistools import (
gf_int, gf_crt)
from sympy.polys.polyerrors import (
MultivariatePolynomialError,
HeuristicGCDFailed,
HomomorphismFailed,
NotInvertible,
DomainError)
from sympy.polys.polyconfig import query
from sympy.utilities import cythonized
from sympy.ntheory import nextprime
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 sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dup_half_gcdex
>>> f = QQ.map([1, -2, -6, 12, 15])
>>> g = QQ.map([1, 1, -4, -4])
>>> dup_half_gcdex(f, g, QQ)
([-1/5, 3/5], [1/1, 1/1])
"""
if not (K.has_Field or not K.is_Exact):
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 dmp_half_gcdex(f, g, u, K):
"""
Half extended Euclidean algorithm in `F[X]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dmp_half_gcdex
"""
if not u:
return dup_half_gcdex(f, g, K)
else:
raise MultivariatePolynomialError(f, g)
def dup_gcdex(f, g, K):
"""
Extended Euclidean algorithm in `F[x]`.
Returns ``(s, t, h)`` such that ``h = gcd(f, g)`` and ``s*f + t*g = h``.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dup_gcdex
>>> f = QQ.map([1, -2, -6, 12, 15])
>>> g = QQ.map([1, 1, -4, -4])
>>> dup_gcdex(f, g, QQ)
([-1/5, 3/5], [1/5, -6/5, 2/1], [1/1, 1/1])
"""
s, h = dup_half_gcdex(f, g, K)
F = dup_sub_mul(h, s, f, K)
t = dup_quo(F, g, K)
return s, t, h
def dmp_gcdex(f, g, u, K):
"""
Extended Euclidean algorithm in `F[X]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dmp_gcdex
"""
if not u:
return dup_gcdex(f, g, K)
else:
raise MultivariatePolynomialError(f, g)
def dup_invert(f, g, K):
"""
Compute multiplicative inverse of `f` modulo `g` in `F[x]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dup_invert
>>> f = QQ.map([1, 0, -1])
>>> g = QQ.map([2, -1])
>>> h = QQ.map([1, -1])
>>> dup_invert(f, g, QQ)
[-4/3]
>>> dup_invert(f, h, QQ)
Traceback (most recent call last):
...
NotInvertible: zero divisor
"""
s, h = dup_half_gcdex(f, g, K)
if h == [K.one]:
return dup_rem(s, g, K)
else:
raise NotInvertible("zero divisor")
def dmp_invert(f, g, u, K):
"""
Compute multiplicative inverse of `f` modulo `g` in `F[X]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dmp_invert
"""
if not u:
return dup_invert(f, g, K)
else:
raise MultivariatePolynomialError(f, g)
def dup_euclidean_prs(f, g, K):
"""
Euclidean polynomial remainder sequence (PRS) in `K[x]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dup_euclidean_prs
>>> f = QQ.map([1, 0, 1, 0, -3, -3, 8, 2, -5])
>>> g = QQ.map([3, 0, 5, 0, -4, -9, 21])
>>> prs = dup_euclidean_prs(f, g, QQ)
>>> prs[0]
[1/1, 0/1, 1/1, 0/1, -3/1, -3/1, 8/1, 2/1, -5/1]
>>> prs[1]
[3/1, 0/1, 5/1, 0/1, -4/1, -9/1, 21/1]
>>> prs[2]
[-5/9, 0/1, 1/9, 0/1, -1/3]
>>> prs[3]
[-117/25, -9/1, 441/25]
>>> prs[4]
[233150/19773, -102500/6591]
>>> prs[5]
[-1288744821/543589225]
"""
prs = [f, g]
h = dup_rem(f, g, K)
while h:
prs.append(h)
f, g = g, h
h = dup_rem(f, g, K)
return prs
def dmp_euclidean_prs(f, g, u, K):
"""
Euclidean polynomial remainder sequence (PRS) in `K[X]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dmp_euclidean_prs
"""
if not u:
return dup_euclidean_prs(f, g, K)
else:
raise MultivariatePolynomialError(f, g)
def dup_primitive_prs(f, g, K):
"""
Primitive polynomial remainder sequence (PRS) in `K[x]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_primitive_prs
>>> f = ZZ.map([1, 0, 1, 0, -3, -3, 8, 2, -5])
>>> g = ZZ.map([3, 0, 5, 0, -4, -9, 21])
>>> prs = dup_primitive_prs(f, g, ZZ)
>>> prs[0]
[1, 0, 1, 0, -3, -3, 8, 2, -5]
>>> prs[1]
[3, 0, 5, 0, -4, -9, 21]
>>> prs[2]
[-5, 0, 1, 0, -3]
>>> prs[3]
[13, 25, -49]
>>> prs[4]
[4663, -6150]
>>> prs[5]
[1]
"""
prs = [f, g]
_, h = dup_primitive(dup_prem(f, g, K), K)
while h:
prs.append(h)
f, g = g, h
_, h = dup_primitive(dup_prem(f, g, K), K)
return prs
def dmp_primitive_prs(f, g, u, K):
"""
Primitive polynomial remainder sequence (PRS) in `K[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_primitive_prs
"""
if not u:
return dup_primitive_prs(f, g, K)
else:
raise MultivariatePolynomialError(f, g)
@cythonized("n,m,d,k")
def dup_inner_subresultants(f, g, K):
"""
Subresultant PRS algorithm in `K[x]`.
Computes the subresultant polynomial remainder sequence (PRS) of `f`
and `g`, and the values for `\beta_i` and `\delta_i`. The last two
sequences of values are necessary for computing the resultant in
:func:`dup_prs_resultant`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_inner_subresultants
>>> f = ZZ.map([1, 0, 1])
>>> g = ZZ.map([1, 0, -1])
>>> dup_inner_subresultants(f, g, ZZ)
([[1, 0, 1], [1, 0, -1], [-2]], [-1, -1], [0, 2])
"""
n = dup_degree(f)
m = dup_degree(g)
if n < m:
f, g = g, f
n, m = m, n
R = [f, g]
d = n - m
b = (-K.one)**(d+1)
c = -K.one
B, D = [b], [d]
if not f or not g:
return R, B, D
h = dup_prem(f, g, K)
h = dup_mul_ground(h, b, K)
while h:
k = dup_degree(h)
R.append(h)
lc = dup_LC(g, K)
if not d:
q = c
else:
q = c**(d-1)
c = K.quo((-lc)**d, q)
b = -lc * c**(m-k)
f, g, m, d = g, h, k, m-k
B.append(b)
D.append(d)
h = dup_prem(f, g, K)
h = dup_quo_ground(h, b, K)
return R, B, D
def dup_subresultants(f, g, K):
"""
Computes subresultant PRS of two polynomials in `K[x]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_subresultants
>>> f = ZZ.map([1, 0, 1])
>>> g = ZZ.map([1, 0, -1])
>>> dup_subresultants(f, g, ZZ)
[[1, 0, 1], [1, 0, -1], [-2]]
"""
return dup_inner_subresultants(f, g, K)[0]
@cythonized("s,i,du,dv,dw")
def dup_prs_resultant(f, g, K):
"""
Resultant algorithm in `K[x]` using subresultant PRS.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_prs_resultant
>>> f = ZZ.map([1, 0, 1])
>>> g = ZZ.map([1, 0, -1])
>>> dup_prs_resultant(f, g, ZZ)
(4, [[1, 0, 1], [1, 0, -1], [-2]])
"""
if not f or not g:
return (K.zero, [])
R, B, D = dup_inner_subresultants(f, g, K)
if dup_degree(R[-1]) > 0:
return (K.zero, R)
if R[-2] == [K.one]:
return (dup_LC(R[-1], K), R)
s, i = 1, 1
p, q = K.one, K.one
for b, d in list(zip(B, D))[:-1]:
du = dup_degree(R[i-1])
dv = dup_degree(R[i ])
dw = dup_degree(R[i+1])
if du % 2 and dv % 2:
s = -s
lc, i = dup_LC(R[i], K), i+1
p *= b**dv * lc**(du-dw)
q *= lc**(dv*(1+d))
if s < 0:
p = -p
i = dup_degree(R[-2])
res = dup_LC(R[-1], K)**i
res = K.quo(res*p, q)
return res, R
def dup_resultant(f, g, K):
"""
Computes resultant of two polynomials in `K[x]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_resultant
>>> f = ZZ.map([1, 0, 1])
>>> g = ZZ.map([1, 0, -1])
>>> dup_resultant(f, g, ZZ)
4
"""
return dup_prs_resultant(f, g, K)[0]
@cythonized("u,v,n,m,d,k")
def dmp_inner_subresultants(f, g, u, K):
"""
Subresultant PRS algorithm in `K[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_inner_subresultants
>>> f = ZZ.map([[3, 0], [], [-1, 0, 0, -4]])
>>> g = ZZ.map([[1], [1, 0, 0, 0], [-9]])
>>> a = [[3, 0, 0, 0, 0], [1, 0, -27, 4]]
>>> b = [[-3, 0, 0, -12, 1, 0, -54, 8, 729, -216, 16]]
>>> R = ZZ.map([f, g, a, b])
>>> B = ZZ.map([[-1], [1], [9, 0, 0, 0, 0, 0, 0, 0, 0]])
>>> D = ZZ.map([0, 1, 1])
>>> dmp_inner_subresultants(f, g, 1, ZZ) == (R, B, D)
True
"""
if not u:
return dup_inner_subresultants(f, g, K)
n = dmp_degree(f, u)
m = dmp_degree(g, u)
if n < m:
f, g = g, f
n, m = m, n
R = [f, g]
d = n - m
v = u - 1
b = dmp_pow(dmp_ground(-K.one, v), d+1, v, K)
c = dmp_ground(-K.one, v)
B, D = [b], [d]
if dmp_zero_p(f, u) or dmp_zero_p(g, u):
return R, B, D
h = dmp_prem(f, g, u, K)
h = dmp_mul_term(h, b, 0, u, K)
while not dmp_zero_p(h, u):
k = dmp_degree(h, u)
R.append(h)
lc = dmp_LC(g, K)
p = dmp_pow(dmp_neg(lc, v, K), d, v, K)
if not d:
q = c
else:
q = dmp_pow(c, d-1, v, K)
c = dmp_quo(p, q, v, K)
b = dmp_mul(dmp_neg(lc, v, K),
dmp_pow(c, m-k, v, K), v, K)
f, g, m, d = g, h, k, m-k
B.append(b)
D.append(d)
h = dmp_prem(f, g, u, K)
h = [ dmp_quo(ch, b, v, K) for ch in h ]
return R, B, D
@cythonized("u")
def dmp_subresultants(f, g, u, K):
"""
Computes subresultant PRS of two polynomials in `K[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_subresultants
>>> f = [[3, 0], [], [-1, 0, 0, -4]]
>>> g = [[1], [1, 0, 0, 0], [-9]]
>>> a = [[3, 0, 0, 0, 0], [1, 0, -27, 4]]
>>> b = [[-3, 0, 0, -12, 1, 0, -54, 8, 729, -216, 16]]
>>> dmp_subresultants(f, g, 1, ZZ) == [f, g, a, b]
True
"""
return dmp_inner_subresultants(f, g, u, K)[0]
@cythonized("u,v,s,i,d,du,dv,dw")
def dmp_prs_resultant(f, g, u, K):
"""
Resultant algorithm in `K[X]` using subresultant PRS.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_prs_resultant
>>> f = ZZ.map([[3, 0], [], [-1, 0, 0, -4]])
>>> g = ZZ.map([[1], [1, 0, 0, 0], [-9]])
>>> a = ZZ.map([[3, 0, 0, 0, 0], [1, 0, -27, 4]])
>>> b = ZZ.map([[-3, 0, 0, -12, 1, 0, -54, 8, 729, -216, 16]])
>>> dmp_prs_resultant(f, g, 1, ZZ) == (b[0], [f, g, a, b])
True
"""
if not u:
return dup_prs_resultant(f, g, K)
if dmp_zero_p(f, u) or dmp_zero_p(g, u):
return (dmp_zero(u-1), [])
R, B, D = dmp_inner_subresultants(f, g, u, K)
if dmp_degree(R[-1], u) > 0:
return (dmp_zero(u-1), R)
if dmp_one_p(R[-2], u, K):
return (dmp_LC(R[-1], K), R)
s, i, v = 1, 1, u-1
p = dmp_one(v, K)
q = dmp_one(v, K)
for b, d in list(zip(B, D))[:-1]:
du = dmp_degree(R[i-1], u)
dv = dmp_degree(R[i ], u)
dw = dmp_degree(R[i+1], u)
if du % 2 and dv % 2:
s = -s
lc, i = dmp_LC(R[i], K), i+1
p = dmp_mul(dmp_mul(p, dmp_pow(b, dv, v, K), v, K),
dmp_pow(lc, du-dw, v, K), v, K)
q = dmp_mul(q, dmp_pow(lc, dv*(1+d), v, K), v, K)
_, p, q = dmp_inner_gcd(p, q, v, K)
if s < 0:
p = dmp_neg(p, v, K)
i = dmp_degree(R[-2], u)
res = dmp_pow(dmp_LC(R[-1], K), i, v, K)
res = dmp_quo(dmp_mul(res, p, v, K), q, v, K)
return res, R
@cythonized("u,v,n,m,N,M,B")
def dmp_zz_modular_resultant(f, g, p, u, K):
"""
Compute resultant of `f` and `g` modulo a prime `p`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_zz_modular_resultant
>>> f = ZZ.map([[1], [1, 2]])
>>> g = ZZ.map([[2, 1], [3]])
>>> dmp_zz_modular_resultant(f, g, ZZ(5), 1, ZZ)
[-2, 0, 1]
"""
if not u:
return gf_int(dup_prs_resultant(f, g, K)[0] % p, p)
v = u - 1
n = dmp_degree(f, u)
m = dmp_degree(g, u)
N = dmp_degree_in(f, 1, u)
M = dmp_degree_in(g, 1, u)
B = n*M + m*N
D, a = [K.one], -K.one
r = dmp_zero(v)
while dup_degree(D) <= B:
while True:
a += K.one
if a == p:
raise HomomorphismFailed('no luck')
F = dmp_eval_in(f, gf_int(a, p), 1, u, K)
if dmp_degree(F, v) == n:
G = dmp_eval_in(g, gf_int(a, p), 1, u, K)
if dmp_degree(G, v) == m:
break
R = dmp_zz_modular_resultant(F, G, p, v, K)
e = dmp_eval(r, a, v, K)
if not v:
R = dup_strip([R])
e = dup_strip([e])
else:
R = [R]
e = [e]
d = K.invert(dup_eval(D, a, K), p)
d = dup_mul_ground(D, d, K)
d = dmp_raise(d, v, 0, K)
c = dmp_mul(d, dmp_sub(R, e, v, K), v, K)
r = dmp_add(r, c, v, K)
r = dmp_ground_trunc(r, p, v, K)
D = dup_mul(D, [K.one, -a], K)
D = dup_trunc(D, p, K)
return r
def _collins_crt(r, R, P, p, K):
"""Wrapper of CRT for Collins's resultant algorithm. """
return gf_int(gf_crt([r, R], [P, p], K), P*p)
@cythonized("u,v,n,m")
def dmp_zz_collins_resultant(f, g, u, K):
"""
Collins's modular resultant algorithm in `Z[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_zz_collins_resultant
>>> f = ZZ.map([[1], [1, 2]])
>>> g = ZZ.map([[2, 1], [3]])
>>> dmp_zz_collins_resultant(f, g, 1, ZZ)
[-2, -5, 1]
"""
n = dmp_degree(f, u)
m = dmp_degree(g, u)
if n < 0 or m < 0:
return dmp_zero(u-1)
A = dmp_max_norm(f, u, K)
B = dmp_max_norm(g, u, K)
a = dmp_ground_LC(f, u, K)
b = dmp_ground_LC(g, u, K)
v = u - 1
B = K(2)*K.factorial(n+m)*A**m*B**n
r, p, P = dmp_zero(v), K.one, K.one
while P <= B:
p = K(nextprime(p))
while not (a % p) or not (b % p):
p = K(nextprime(p))
F = dmp_ground_trunc(f, p, u, K)
G = dmp_ground_trunc(g, p, u, K)
try:
R = dmp_zz_modular_resultant(F, G, p, u, K)
except HomomorphismFailed:
continue
if K.is_one(P):
r = R
else:
r = dmp_apply_pairs(r, R, _collins_crt, (P, p, K), v, K)
P *= p
return r
@cythonized("u,n,m")
def dmp_qq_collins_resultant(f, g, u, K0):
"""
Collins's modular resultant algorithm in `Q[X]`.
**Examples**
>>> from sympy.polys.domains import QQ
>>> from sympy.polys.euclidtools import dmp_qq_collins_resultant
>>> f = [[QQ(1,2)], [QQ(1), QQ(2,3)]]
>>> g = [[QQ(2), QQ(1)], [QQ(3)]]
>>> dmp_qq_collins_resultant(f, g, 1, QQ)
[-2/1, -7/3, 5/6]
"""
n = dmp_degree(f, u)
m = dmp_degree(g, u)
if n < 0 or m < 0:
return dmp_zero(u-1)
K1 = K0.get_ring()
cf, f = dmp_clear_denoms(f, u, K0, K1)
cg, g = dmp_clear_denoms(g, u, K0, K1)
f = dmp_convert(f, u, K0, K1)
g = dmp_convert(g, u, K0, K1)
r = dmp_zz_collins_resultant(f, g, u, K1)
r = dmp_convert(r, u-1, K1, K0)
c = K0.convert(cf**m * cg**n, K1)
return dmp_quo_ground(r, c, u-1, K0)
@cythonized("u")
def dmp_resultant(f, g, u, K):
"""
Computes resultant of two polynomials in `K[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_resultant
>>> f = ZZ.map([[3, 0], [], [-1, 0, 0, -4]])
>>> g = ZZ.map([[1], [1, 0, 0, 0], [-9]])
>>> dmp_resultant(f, g, 1, ZZ)
[-3, 0, 0, -12, 1, 0, -54, 8, 729, -216, 16]
"""
if not u:
return dup_resultant(f, g, K)
if K.has_Field:
if K.is_QQ and query('USE_COLLINS_RESULTANT'):
return dmp_qq_collins_resultant(f, g, u, K)
else:
if K.is_ZZ and query('USE_COLLINS_RESULTANT'):
return dmp_zz_collins_resultant(f, g, u, K)
return dmp_prs_resultant(f, g, u, K)[0]
@cythonized("d,s")
def dup_discriminant(f, K):
"""
Computes discriminant of a polynomial in `K[x]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_discriminant
>>> dup_discriminant([ZZ(1), ZZ(2), ZZ(3)], ZZ)
-8
"""
d = dup_degree(f)
if d <= 0:
return K.zero
else:
s = (-1)**((d*(d-1)) // 2)
c = dup_LC(f, K)
r = dup_resultant(f, dup_diff(f, 1, K), K)
return K.quo(r, c*K(s))
@cythonized("u,v,d,s")
def dmp_discriminant(f, u, K):
"""
Computes discriminant of a polynomial in `K[X]`.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dmp_discriminant
>>> f = ZZ.map([[[[1]], [[]]], [[[1], []]], [[[1, 0]]]])
>>> dmp_discriminant(f, 3, ZZ)
[[[-4, 0]], [[1], [], []]]
"""
if not u:
return dup_discriminant(f, K)
d, v = dmp_degree(f, u), u-1
if d <= 0:
return dmp_zero(v)
else:
s = (-1)**((d*(d-1)) // 2)
c = dmp_LC(f, K)
r = dmp_resultant(f, dmp_diff(f, 1, u, K), u, K)
c = dmp_mul_ground(c, K(s), v, K)
return dmp_quo(r, c, v, K)
def _dup_rr_trivial_gcd(f, g, K):
"""Handle trivial cases in GCD algorithm over a ring. """
if not (f or g):
return [], [], []
elif not f:
if K.is_nonnegative(dup_LC(g, K)):
return g, [], [K.one]
else:
return dup_neg(g, K), [], [-K.one]
elif not g:
if K.is_nonnegative(dup_LC(f, K)):
return f, [K.one], []
else:
return dup_neg(f, K), [-K.one], []
return None
def _dup_ff_trivial_gcd(f, g, K):
"""Handle trivial cases in GCD algorithm over a field. """
if not (f or g):
return [], [], []
elif not f:
return dup_monic(g, K), [], [dup_LC(g, K)]
elif not g:
return dup_monic(f, K), [dup_LC(f, K)], []
else:
return None
@cythonized("u")
def _dmp_rr_trivial_gcd(f, g, u, K):
"""Handle trivial cases in GCD algorithm over a ring. """
zero_f = dmp_zero_p(f, u)
zero_g = dmp_zero_p(g, u)
if zero_f and zero_g:
return tuple(dmp_zeros(3, u, K))
elif zero_f:
if K.is_nonnegative(dmp_ground_LC(g, u, K)):
return g, dmp_zero(u), dmp_one(u, K)
else:
return dmp_neg(g, u, K), dmp_zero(u), dmp_ground(-K.one, u)
elif zero_g:
if K.is_nonnegative(dmp_ground_LC(f, u, K)):
return f, dmp_one(u, K), dmp_zero(u)
else:
return dmp_neg(f, u, K), dmp_ground(-K.one, u), dmp_zero(u)
elif query('USE_SIMPLIFY_GCD'):
return _dmp_simplify_gcd(f, g, u, K)
else:
return None
@cythonized("u")
def _dmp_ff_trivial_gcd(f, g, u, K):
"""Handle trivial cases in GCD algorithm over a field. """
zero_f = dmp_zero_p(f, u)
zero_g = dmp_zero_p(g, u)
if zero_f and zero_g:
return tuple(dmp_zeros(3, u, K))
elif zero_f:
return (dmp_ground_monic(g, u, K),
dmp_zero(u),
dmp_ground(dmp_ground_LC(g, u, K), u))
elif zero_g:
return (dmp_ground_monic(f, u, K),
dmp_ground(dmp_ground_LC(f, u, K), u),
dmp_zero(u))
elif query('USE_SIMPLIFY_GCD'):
return _dmp_simplify_gcd(f, g, u, K)
else:
return None
@cythonized("u,v,df,dg")
def _dmp_simplify_gcd(f, g, u, K):
"""Try to eliminate `x_0` from GCD computation in `K[X]`. """
df = dmp_degree(f, u)
dg = dmp_degree(g, u)
if df > 0 and dg > 0:
return None
if not (df or dg):
F = dmp_LC(f, K)
G = dmp_LC(g, K)
else:
if not df:
F = dmp_LC(f, K)
G = dmp_content(g, u, K)
else:
F = dmp_content(f, u, K)
G = dmp_LC(g, K)
v = u - 1
h = dmp_gcd(F, G, v, K)
cff = [ dmp_quo(cf, h, v, K) for cf in f ]
cfg = [ dmp_quo(cg, h, v, K) for cg in g ]
return [h], cff, cfg
def dup_rr_prs_gcd(f, g, K):
"""
Computes polynomial GCD using subresultants over a ring.
Returns ``(h, cff, cfg)`` such that ``a = gcd(f, g)``, ``cff = quo(f, h)``,
and ``cfg = quo(g, h)``.
**Examples**
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.euclidtools import dup_rr_prs_gcd
>>> f = ZZ.map([1, 0, -1])
>>> g = ZZ.map([1, -3, 2])
>>> dup_rr_prs_gcd(f, g, ZZ)
([1, -1], [1, 1], [1, -2])
"""
result = _dup_rr_trivial_gcd(f, g, K)
if result is not None:
return result
fc, F = dup_primitive(f, K)
gc, G = dup_primitive(g, K)
c = K.gcd(fc, gc)
h = dup_subresultants(F, G, K)[-1]
_, h = dup_primitive(h, K)