def matrix_fglm(F, u, O_from, O_to, K):
"""
Converts the reduced Groebner basis ``F`` of a zero-dimensional
ideal w.r.t. ``O_from`` to a reduced Groebner basis
w.r.t. ``O_to``.
**References**
J.C. Faugere, P. Gianni, D. Lazard, T. Mora (1994). Efficient
Computation of Zero-dimensional Groebner Bases by Change of
Ordering
J.C. Faugere's lecture notes:
http://www-salsa.lip6.fr/~jcf/Papers/2010_MPRI5e.pdf
"""
old_basis = _basis(F, u, O_from, K)
M = _representing_matrices(old_basis, F, u, O_from, K)
# V contains the normalforms (wrt O_from) of S
S = [(0,) * (u + 1)]
V = [[K.one] + [K.zero] * (len(old_basis) - 1)]
G = []
L = [(i, 0) for i in xrange(u + 1)] # (i, j) corresponds to x_i * S[j]
L.sort(key=lambda (k, l): O_to(_incr_k(S[l], k)), reverse=True)
t = L.pop()
P = _identity_matrix(len(old_basis), K)
while True:
s = len(S)
v = _matrix_mul(M[t[0]], V[t[1]], K)
_lambda = _matrix_mul(P, v, K)
if all(_lambda[i] == K.zero for i in xrange(s, len(old_basis))):
# there is a linear combination of v by V
lt = [(_incr_k(S[t[1]], t[0]), K.one)]
rest = sdp_strip(sdp_sort([(S[i], _lambda[i]) for i in xrange(s)], O_to))
g = sdp_sub(lt, rest, u, O_to, K)
if g != []:
G.append(g)
else:
# v is linearly independant from V
P = _update(s, _lambda, P, K)
S.append(_incr_k(S[t[1]], t[0]))
V.append(v)
L.extend([(i, s) for i in xrange(u + 1)])
L = list(set(L))
L.sort(key=lambda (k, l): O_to(_incr_k(S[l], k)), reverse=True)
L = [(k, l) for (k, l) in L if all(monomial_div(_incr_k(S[l], k), sdp_LM(g, u)) is None for g in G)]
if not L:
G = [sdp_monic(g, K) for g in G]
return sorted(G, key=lambda g: O_to(sdp_LM(g, u)), reverse=True)
t = L.pop()
def sdp_spoly(p1, p2, u, O, K):
"""
Compute LCM(LM(p1), LM(p2))/LM(p1)*p1 - LCM(LM(p1), LM(p2))/LM(p2)*p2
This is the S-poly provided p1 and p2 are monic
"""
LM1 = sdp_LM(p1, u)
LM2 = sdp_LM(p2, u)
LCM12 = monomial_lcm(LM1, LM2)
m1 = monomial_div(LCM12, LM1)
m2 = monomial_div(LCM12, LM2)
s1 = sdp_mul_term(p1, (m1, K.one), u, O, K)
s2 = sdp_mul_term(p2, (m2, K.one), u, O, K)
s = sdp_sub(s1, s2, u, O, K)
return s
def sdp_spoly(p1, p2, u, O, K):
"""
Compute LCM(LM(p1), LM(p2))/LM(p1)*p1 - LCM(LM(p1), LM(p2))/LM(p2)*p2
This is the S-poly provided p1 and p2 are monic
"""
LM1 = sdp_LM(p1, u)
LM2 = sdp_LM(p2, u)
LCM12 = monomial_lcm(LM1, LM2)
m1 = monomial_div(LCM12, LM1)
m2 = monomial_div(LCM12, LM2)
s1 = sdp_mul_term(p1, (m1, K.one), u, O, K)
s2 = sdp_mul_term(p2, (m2, K.one), u, O, K)
s = sdp_sub(s1, s2, u, O, K)
return s
def lbp_sub(f, g, u, O, K):
"""
Subtract labeled polynomial g from f.
The signature and number of the difference of f and g are signature
and number of the maximum of f and g, w.r.t. lbp_cmp.
"""
if sig_cmp(Sign(f), Sign(g), O) < 0:
max_poly = g
else:
max_poly = f
ret = sdp_sub(Polyn(f), Polyn(g), u, O, K)
return lbp(Sign(max_poly), ret, Num(max_poly))
def lbp_sub(f, g, u, O, K):
"""
Subtract labeled polynomial g from f.
The signature and number of the difference of f and g are signature
and number of the maximum of f and g, w.r.t. lbp_cmp.
"""
if sig_cmp(Sign(f), Sign(g), O) < 0:
max_poly = g
else:
max_poly = f
ret = sdp_sub(Polyn(f), Polyn(g), u, O, K)
return lbp(Sign(max_poly), ret, Num(max_poly))
def matrix_fglm(F, u, O_from, O_to, K):
"""
Converts the reduced Groebner basis ``F`` of a zero-dimensional
ideal w.r.t. ``O_from`` to a reduced Groebner basis
w.r.t. ``O_to``.
**References**
J.C. Faugere, P. Gianni, D. Lazard, T. Mora (1994). Efficient
Computation of Zero-dimensional Groebner Bases by Change of
Ordering
J.C. Faugere's lecture notes:
http://www-salsa.lip6.fr/~jcf/Papers/2010_MPRI5e.pdf
"""
old_basis = _basis(F, u, O_from, K)
M = _representing_matrices(old_basis, F, u, O_from, K)
# V contains the normalforms (wrt O_from) of S
S = [(0, ) * (u + 1)]
V = [[K.one] + [K.zero] * (len(old_basis) - 1)]
G = []
L = [(i, 0) for i in xrange(u + 1)] # (i, j) corresponds to x_i * S[j]
L.sort(key=lambda (k, l): O_to(_incr_k(S[l], k)), reverse=True)
t = L.pop()
P = _identity_matrix(len(old_basis), K)
while True:
s = len(S)
v = _matrix_mul(M[t[0]], V[t[1]], K)
_lambda = _matrix_mul(P, v, K)
if all([_lambda[i] == K.zero for i in xrange(s, len(old_basis))]):
# there is a linear combination of v by V
lt = [(_incr_k(S[t[1]], t[0]), K.one)]
rest = sdp_strip(
sdp_sort([(S[i], _lambda[i]) for i in xrange(s)], O_to))
g = sdp_sub(lt, rest, u, O_to, K)
if g != []:
G.append(g)
else:
# v is linearly independant from V
P = _update(s, _lambda, P, K)
S.append(_incr_k(S[t[1]], t[0]))
V.append(v)
L.extend([(i, s) for i in xrange(u + 1)])
L = list(set(L))
L.sort(key=lambda (k, l): O_to(_incr_k(S[l], k)), reverse=True)
L = [(k, l) for (k, l) in L if \
all([monomial_div(_incr_k(S[l], k), sdp_LM(g, u)) is None for g in G])]
if L == []:
return sorted(G, key=lambda g: O_to(sdp_LM(g, u)), reverse=True)
t = L.pop()
