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lyndon_word.py
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lyndon_word.py
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# -*- coding: utf-8 -*-
"""
Lyndon words
"""
#*****************************************************************************
# Copyright (C) 2007 Mike Hansen <mhansen@gmail.com>,
#
# Distributed under the terms of the GNU General Public License (GPL)
#
# This code is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# The full text of the GPL is available at:
#
# http://www.gnu.org/licenses/
#*****************************************************************************
from sage.combinat.combinat import CombinatorialClass
from sage.combinat.composition import Composition, Compositions
from sage.rings.all import divisors, gcd, moebius, Integer
from sage.rings.arith import factorial
from sage.misc.all import prod
import __builtin__
import sage.combinat.necklace
from sage.combinat.integer_vector import IntegerVectors
from sage.combinat.words.word import FiniteWord_list
from sage.combinat.words.words import Words_all, FiniteWords_length_k_over_OrderedAlphabet
from sage.combinat.words.alphabet import build_alphabet
def LyndonWords(e=None, k=None):
"""
Returns the combinatorial class of Lyndon words.
A Lyndon word `w` is a word that is lexicographically less than all of
its rotations. Equivalently, whenever `w` is split into two non-empty
substrings, `w` is lexicographically less than the right substring.
INPUT:
- no input at all
or
- ``e`` - integer, size of alphabet
- ``k`` - integer, length of the words
or
- ``e`` - a composition
OUTPUT:
A combinatorial class of Lyndon words.
EXAMPLES::
sage: LyndonWords()
Lyndon words
If e is an integer, then e specifies the length of the
alphabet; k must also be specified in this case::
sage: LW = LyndonWords(3,3); LW
Lyndon words from an alphabet of size 3 of length 3
sage: LW.first()
word: 112
sage: LW.last()
word: 233
sage: LW.random_element() # random
word: 112
sage: LW.cardinality()
8
If e is a (weak) composition, then it returns the class of Lyndon
words that have evaluation e::
sage: LyndonWords([2, 0, 1]).list()
[word: 113]
sage: LyndonWords([2, 0, 1, 0, 1]).list()
[word: 1135, word: 1153, word: 1315]
sage: LyndonWords([2, 1, 1]).list()
[word: 1123, word: 1132, word: 1213]
"""
if e is None and k is None:
return LyndonWords_class()
elif isinstance(e, (int, Integer)):
if e > 0:
if not isinstance(k, (int, Integer)):
raise TypeError("k must be a non-negative integer")
if k < 0:
raise TypeError("k must be a non-negative integer")
return LyndonWords_nk(e, k)
elif e in Compositions():
return LyndonWords_evaluation(e)
raise TypeError("e must be a positive integer or a composition")
class LyndonWord(FiniteWord_list):
def __init__(self, data, check=True):
r"""
Construction of a Lyndon word.
INPUT:
- ``data`` - list
- ``check`` - bool (optional, default: True) if True, a
verification that the input data represent a Lyndon word.
OUTPUT:
A Lyndon word.
EXAMPLES::
sage: LyndonWord([1,2,2])
word: 122
sage: LyndonWord([1,2,3])
word: 123
sage: LyndonWord([2,1,2,3])
Traceback (most recent call last):
...
ValueError: Not a Lyndon word
If check is False, then no verification is done::
sage: LyndonWord([2,1,2,3], check=False)
word: 2123
"""
super(LyndonWord,self).__init__(parent=LyndonWords(),data=data)
if check and not self.is_lyndon():
raise ValueError("Not a Lyndon word")
class LyndonWords_class(Words_all):
def __repr__(self):
r"""
String representation.
EXAMPLES::
sage: LyndonWords()
Lyndon words
"""
return "Lyndon words"
def __contains__(self, x):
"""
TESTS::
sage: LW33 = LyndonWords(3,3)
sage: all([lw in LyndonWords() for lw in LW33])
True
"""
try:
return LyndonWord(x)
except ValueError:
return False
class LyndonWords_evaluation(CombinatorialClass):
def __init__(self, e):
"""
TESTS::
sage: LW21 = LyndonWords([2,1]); LW21
Lyndon words with evaluation [2, 1]
sage: LW21 == loads(dumps(LW21))
True
"""
self.e = Composition(e)
def __repr__(self):
"""
TESTS::
sage: repr(LyndonWords([2,1,1]))
'Lyndon words with evaluation [2, 1, 1]'
"""
return "Lyndon words with evaluation %s"%self.e
def __contains__(self, x):
"""
EXAMPLES::
sage: [1,2,1,2] in LyndonWords([2,2])
False
sage: [1,1,2,2] in LyndonWords([2,2])
True
sage: all([ lw in LyndonWords([2,1,3,1]) for lw in LyndonWords([2,1,3,1])])
True
"""
try:
w = LyndonWord(x)
except ValueError:
return False
ed = w.evaluation_dict()
for (i,a) in enumerate(self.e):
if ed[i+1] != a:
return False
return True
def cardinality(self):
"""
Returns the number of Lyndon words with the evaluation e.
EXAMPLES::
sage: LyndonWords([]).cardinality()
0
sage: LyndonWords([2,2]).cardinality()
1
sage: LyndonWords([2,3,2]).cardinality()
30
Check to make sure that the count matches up with the number of
Lyndon words generated.
::
sage: comps = [[],[2,2],[3,2,7],[4,2]]+Compositions(4).list()
sage: lws = [ LyndonWords(comp) for comp in comps]
sage: all( [ lw.cardinality() == len(lw.list()) for lw in lws] )
True
"""
evaluation = self.e
le = __builtin__.list(evaluation)
if len(evaluation) == 0:
return 0
n = sum(evaluation)
return sum([moebius(j)*factorial(n/j) / prod([factorial(ni/j) for ni in evaluation]) for j in divisors(gcd(le))])/n
def __iter__(self):
"""
An iterator for the Lyndon words with evaluation e.
EXAMPLES::
sage: LyndonWords([1]).list() #indirect doctest
[word: 1]
sage: LyndonWords([2]).list() #indirect doctest
[]
sage: LyndonWords([3]).list() #indirect doctest
[]
sage: LyndonWords([3,1]).list() #indirect doctest
[word: 1112]
sage: LyndonWords([2,2]).list() #indirect doctest
[word: 1122]
sage: LyndonWords([1,3]).list() #indirect doctest
[word: 1222]
sage: LyndonWords([3,3]).list() #indirect doctest
[word: 111222, word: 112122, word: 112212]
sage: LyndonWords([4,3]).list() #indirect doctest
[word: 1111222, word: 1112122, word: 1112212, word: 1121122, word: 1121212]
TESTS:
Check that :trac:`12997` is fixed::
sage: LyndonWords([0,1]).list()
[word: 2]
sage: LyndonWords([0,2]).list()
[]
sage: LyndonWords([0,0,1,0,1]).list()
[word: 35]
"""
if self.e == []:
return
k = 0
while self.e[k] == 0:
k += 1
for z in necklace._sfc(self.e[k:], equality=True):
yield LyndonWord([i+k+1 for i in z], check=False)
class LyndonWords_nk(FiniteWords_length_k_over_OrderedAlphabet):
def __init__(self, n, k):
"""
TESTS::
sage: LW23 = LyndonWords(2,3); LW23
Lyndon words from an alphabet of size 2 of length 3
sage: LW23== loads(dumps(LW23))
True
"""
self.n = Integer(n)
self.k = Integer(k)
alphabet = build_alphabet(range(1,self.n+1))
super(LyndonWords_nk,self).__init__(alphabet,self.k)
def __repr__(self):
"""
TESTS::
sage: repr(LyndonWords(2, 3))
'Lyndon words from an alphabet of size 2 of length 3'
"""
return "Lyndon words from an alphabet of size %s of length %s"%(self.n, self.k)
def __contains__(self, x):
"""
TESTS::
sage: LW33 = LyndonWords(3,3)
sage: all([lw in LW33 for lw in LW33])
True
"""
try:
w = LyndonWord(x)
return w.length() == self.k and len(set(w)) <= self.n
except ValueError:
return False
def cardinality(self):
"""
TESTS::
sage: [ LyndonWords(3,i).cardinality() for i in range(1, 11) ]
[3, 3, 8, 18, 48, 116, 312, 810, 2184, 5880]
"""
if self.k == 0:
return 1
else:
s = 0
for d in divisors(self.k):
s += moebius(d)*(self.n**(self.k/d))
return s/self.k
def __iter__(self):
"""
TESTS::
sage: LyndonWords(3,3).list() # indirect doctest
[word: 112, word: 113, word: 122, word: 123, word: 132, word: 133, word: 223, word: 233]
"""
for c in IntegerVectors(self.k, self.n):
cf = [x for x in c if x != 0]
nonzero_indices = []
for i in range(len(c)):
if c[i] != 0:
nonzero_indices.append(i)
for lw in LyndonWords_evaluation(cf):
yield LyndonWord([nonzero_indices[x-1]+1 for x in lw], check=False)
def StandardBracketedLyndonWords(n, k):
"""
Returns the combinatorial class of standard bracketed Lyndon words
from [1, ..., n] of length k. These are in one to one
correspondence with the Lyndon words and form a basis for the
subspace of degree k of the free Lie algebra of rank n.
EXAMPLES::
sage: SBLW33 = StandardBracketedLyndonWords(3,3); SBLW33
Standard bracketed Lyndon words from an alphabet of size 3 of length 3
sage: SBLW33.first()
[1, [1, 2]]
sage: SBLW33.last()
[[2, 3], 3]
sage: SBLW33.cardinality()
8
sage: SBLW33.random_element()
[1, [1, 2]]
"""
return StandardBracketedLyndonWords_nk(n,k)
class StandardBracketedLyndonWords_nk(CombinatorialClass):
def __init__(self, n, k):
"""
TESTS::
sage: SBLW = StandardBracketedLyndonWords(3, 2)
sage: SBLW == loads(dumps(SBLW))
True
"""
self.n = Integer(n)
self.k = Integer(k)
def __repr__(self):
"""
TESTS::
sage: repr(StandardBracketedLyndonWords(3, 3))
'Standard bracketed Lyndon words from an alphabet of size 3 of length 3'
"""
return "Standard bracketed Lyndon words from an alphabet of size %s of length %s"%(self.n, self.k)
def cardinality(self):
"""
EXAMPLES::
sage: StandardBracketedLyndonWords(3, 3).cardinality()
8
sage: StandardBracketedLyndonWords(3, 4).cardinality()
18
"""
return LyndonWords_nk(self.n,self.k).cardinality()
def __iter__(self):
"""
EXAMPLES::
sage: StandardBracketedLyndonWords(3, 3).list()
[[1, [1, 2]],
[1, [1, 3]],
[[1, 2], 2],
[1, [2, 3]],
[[1, 3], 2],
[[1, 3], 3],
[2, [2, 3]],
[[2, 3], 3]]
"""
for lw in LyndonWords_nk(self.n, self.k):
yield standard_bracketing(lw)
def standard_bracketing(lw):
"""
Returns the standard bracketing of a Lyndon word lw.
EXAMPLES::
sage: import sage.combinat.lyndon_word as lyndon_word
sage: map( lyndon_word.standard_bracketing, LyndonWords(3,3) )
[[1, [1, 2]],
[1, [1, 3]],
[[1, 2], 2],
[1, [2, 3]],
[[1, 3], 2],
[[1, 3], 3],
[2, [2, 3]],
[[2, 3], 3]]
"""
if len(lw) == 1:
return lw[0]
for i in range(1,len(lw)):
if lw[i:] in LyndonWords():
return [ standard_bracketing( lw[:i] ), standard_bracketing(lw[i:]) ]