def best_linear_code_in_guava(n, k, F):
r"""
Returns the linear code of length ``n``, dimension ``k`` over field ``F``
with the maximal minimum distance which is known to the GAP package GUAVA.
The function uses the tables described in ``bounds_on_minimum_distance_in_guava`` to
construct this code. This requires the optional GAP package GUAVA.
INPUT:
- ``n`` -- the length of the code to look up
- ``k`` -- the dimension of the code to look up
- ``F`` -- the base field of the code to look up
OUTPUT:
- A :class:`LinearCode` which is a best linear code of the given parameters known to GUAVA.
EXAMPLES::
sage: codes.databases.best_linear_code_in_guava(10,5,GF(2)) # long time; optional - gap_packages (Guava package)
[10, 5] linear code over GF(2)
sage: gap.eval("C:=BestKnownLinearCode(10,5,GF(2))") # long time; optional - gap_packages (Guava package)
'a linear [10,5,4]2..4 shortened code'
This means that the best possible binary linear code of length 10 and
dimension 5 is a code with minimum distance 4 and covering radius s somewhere
between 2 and 4. Use ``bounds_on_minimum_distance_in_guava(10,5,GF(2))``
for further details.
"""
if not is_package_installed('gap_packages'):
raise PackageNotFoundError('gap_packages')
gap.load_package("guava")
q = F.order()
C = gap("BestKnownLinearCode(%s,%s,GF(%s))"%(n,k,q))
from .linear_code import LinearCode
return LinearCode(C.GeneratorMat()._matrix_(F))
def best_linear_code_in_guava(n, k, F):
r"""
Returns the linear code of length ``n``, dimension ``k`` over field ``F``
with the maximal minimum distance which is known to the GAP package GUAVA.
The function uses the tables described in ``bounds_on_minimum_distance_in_guava`` to
construct this code. This requires the optional GAP package GUAVA.
INPUT:
- ``n`` -- the length of the code to look up
- ``k`` -- the dimension of the code to look up
- ``F`` -- the base field of the code to look up
OUTPUT:
- A :class:`LinearCode` which is a best linear code of the given parameters known to GUAVA.
EXAMPLES::
sage: codes.databases.best_linear_code_in_guava(10,5,GF(2)) # long time; optional - gap_packages (Guava package)
[10, 5] linear code over GF(2)
sage: gap.eval("C:=BestKnownLinearCode(10,5,GF(2))") # long time; optional - gap_packages (Guava package)
'a linear [10,5,4]2..4 shortened code'
This means that the best possible binary linear code of length 10 and
dimension 5 is a code with minimum distance 4 and covering radius s somewhere
between 2 and 4. Use ``bounds_on_minimum_distance_in_guava(10,5,GF(2))``
for further details.
"""
if not is_package_installed('gap_packages'):
raise PackageNotFoundError('gap_packages')
gap.load_package("guava")
q = F.order()
C = gap("BestKnownLinearCode(%s,%s,GF(%s))" % (n, k, q))
from .linear_code import LinearCode
return LinearCode(C.GeneratorMat()._matrix_(F))
def solve(self,state, algorithm='default'):
r"""
Solves the cube in the ``state``, given as a dictionary
as in ``legal``. See the ``solve`` method
of the RubiksCube class for more details.
This may use GAP's ``EpimorphismFromFreeGroup`` and
``PreImagesRepresentative`` as explained below, if
'gap' is passed in as the algorithm.
This algorithm
#. constructs the free group on 6 generators then computes a
reasonable set of relations which they satisfy
#. computes a homomorphism from the cube group to this free group
quotient
#. takes the cube position, regarded as a group element, and maps
it over to the free group quotient
#. using those relations and tricks from combinatorial group theory
(stabilizer chains), solves the "word problem" for that element.
#. uses python string parsing to rewrite that in cube notation.
The Rubik's cube group has about `4.3 \times 10^{19}`
elements, so this process is time-consuming. See
http://www.gap-system.org/Doc/Examples/rubik.html for an
interesting discussion of some GAP code analyzing the Rubik's
cube.
EXAMPLES::
sage: rubik = CubeGroup()
sage: state = rubik.faces("R")
sage: rubik.solve(state)
'R'
sage: state = rubik.faces("R*U")
sage: rubik.solve(state, algorithm='gap') # long time
'R*U'
You can also check this another (but similar) way using the
``word_problem`` method (eg, G = rubik.group(); g =
G("(3,38,43,19)(5,36,45,21)(8,33,48,24)(25,27,32,30)(26,29,31,28)");
g.word_problem([b,d,f,l,r,u]), though the output will be less
intuitive).
"""
from sage.groups.perm_gps.permgroup import PermutationGroup
from sage.interfaces.all import gap
G = self.group()
try:
g = self.parse(state)
except TypeError:
return "Illegal or syntactically incorrect state. No solution."
if algorithm != 'gap':
C = RubiksCube(g)
return C.solve(algorithm)
hom = G._gap_().EpimorphismFromFreeGroup()
soln = hom.PreImagesRepresentative(gap(str(g)))
# print soln
sol = str(soln)
names = self.gen_names()
for i in range(6):
sol = sol.replace("x%s" % (i+1), names[i])
return sol
def solve(self, state, algorithm='default'):
r"""
Solves the cube in the ``state``, given as a dictionary
as in ``legal``. See the ``solve`` method
of the RubiksCube class for more details.
This may use GAP's ``EpimorphismFromFreeGroup`` and
``PreImagesRepresentative`` as explained below, if
'gap' is passed in as the algorithm.
This algorithm
#. constructs the free group on 6 generators then computes a
reasonable set of relations which they satisfy
#. computes a homomorphism from the cube group to this free group
quotient
#. takes the cube position, regarded as a group element, and maps
it over to the free group quotient
#. using those relations and tricks from combinatorial group theory
(stabilizer chains), solves the "word problem" for that element.
#. uses python string parsing to rewrite that in cube notation.
The Rubik's cube group has about `4.3 \times 10^{19}`
elements, so this process is time-consuming. See
http://www.gap-system.org/Doc/Examples/rubik.html for an
interesting discussion of some GAP code analyzing the Rubik's
cube.
EXAMPLES::
sage: rubik = CubeGroup()
sage: state = rubik.faces("R")
sage: rubik.solve(state)
'R'
sage: state = rubik.faces("R*U")
sage: rubik.solve(state, algorithm='gap') # long time
'R*U'
You can also check this another (but similar) way using the
``word_problem`` method (eg, G = rubik.group(); g =
G("(3,38,43,19)(5,36,45,21)(8,33,48,24)(25,27,32,30)(26,29,31,28)");
g.word_problem([b,d,f,l,r,u]), though the output will be less
intuitive).
"""
from sage.groups.perm_gps.permgroup import PermutationGroup
from sage.interfaces.all import gap
G = self.group()
try:
g = self.parse(state)
except TypeError:
return "Illegal or syntactically incorrect state. No solution."
if algorithm != 'gap':
C = RubiksCube(g)
return C.solve(algorithm)
hom = G._gap_().EpimorphismFromFreeGroup()
soln = hom.PreImagesRepresentative(gap(str(g)))
# print soln
sol = str(soln)
names = self.gen_names()
for i in range(6):
sol = sol.replace("x%s" % (i + 1), names[i])
return sol
