Word morphisms/substitutions¶
This modules implements morphisms over finite and infinite words.
AUTHORS:
Sebastien Labbe (2007-06-01): initial version
Sebastien Labbe (2008-07-01): merged into sage-words
Sebastien Labbe (2008-12-17): merged into sage
Sebastien Labbe (2009-02-03): words next generation
Sebastien Labbe (2009-11-20): allowing the choice of the datatype of the image. Doc improvements.
Stepan Starosta (2012-11-09): growing letters
EXAMPLES:
Creation of a morphism from a dictionary or a string:
sage: n = WordMorphism({0:[0,2,2,1],1:[0,2],2:[2,2,1]})
sage: m = WordMorphism('x->xyxsxss,s->xyss,y->ys')
sage: n
WordMorphism: 0->0221, 1->02, 2->221
sage: m
WordMorphism: s->xyss, x->xyxsxss, y->ys
The codomain may be specified:
sage: WordMorphism({0:[0,2,2,1],1:[0,2],2:[2,2,1]}, codomain=Words([0,1,2,3,4]))
WordMorphism: 0->0221, 1->02, 2->221
Power of a morphism:
sage: n^2
WordMorphism: 0->022122122102, 1->0221221, 2->22122102
Image under a morphism:
sage: m('y')
word: ys
sage: m('xxxsy')
word: xyxsxssxyxsxssxyxsxssxyssys
Iterated image under a morphism:
sage: m('y', 3)
word: ysxyssxyxsxssysxyssxyss
See more examples in the documentation of the call method
(m.__call__?
).
Infinite fixed point of morphism:
sage: fix = m.fixed_point('x')
sage: fix
word: xyxsxssysxyxsxssxyssxyxsxssxyssxyssysxys...
sage: fix.length()
+Infinity
Incidence matrix:
sage: matrix(m)
[2 3 1]
[1 3 0]
[1 1 1]
Many other functionalities…:
sage: m.is_identity()
False
sage: m.is_endomorphism()
True
-
class
sage.combinat.words.morphism.
PeriodicPointIterator
(m, cycle)¶ Bases:
object
(Lazy) constructor of the periodic points of a word morphism.
This class is mainly used in
WordMorphism.periodic_point
andWordMorphism.periodic_points
.EXAMPLES:
sage: from sage.combinat.words.morphism import PeriodicPointIterator sage: s = WordMorphism('a->bacca,b->cba,c->aab') sage: p = PeriodicPointIterator(s, ['a','b','c']) sage: p._cache[0] lazy list ['a', 'a', 'b', ...] sage: p._cache[1] lazy list ['b', 'a', 'c', ...] sage: p._cache[2] lazy list ['c', 'b', 'a', ...]
-
get_iterator
(i)¶ Internal method.
EXAMPLES:
sage: from sage.combinat.words.morphism import PeriodicPointIterator sage: s = WordMorphism('a->bacca,b->cba,c->aab') sage: p = PeriodicPointIterator(s, ['a','b','c']) sage: p.get_iterator(0) <generator object ...get_iterator at ...>
-
-
class
sage.combinat.words.morphism.
WordMorphism
(data, domain=None, codomain=None)¶ Bases:
sage.structure.sage_object.SageObject
WordMorphism class
INPUT:
data
– dict or str or an instance of WordMorphism, the map giving the image of lettersdomain
– (optional:None
) set of words over a given alphabet. IfNone
, the domain alphabet is computed fromdata
and is sorted.codomain
– (optional:None
) set of words over a given alphabet. IfNone
, the codomain alphabet is computed fromdata
and is sorted.
Note
When the domain or the codomain are not explicitly given, it is expected that the letters are comparable because the alphabets of the domain and of the codomain are sorted.
EXAMPLES:
From a dictionary:
sage: n = WordMorphism({0:[0,2,2,1],1:[0,2],2:[2,2,1]}) sage: n WordMorphism: 0->0221, 1->02, 2->221
From a string with
'->'
as separation:sage: m = WordMorphism('x->xyxsxss,s->xyss,y->ys') sage: m WordMorphism: s->xyss, x->xyxsxss, y->ys sage: m.domain() Finite words over {'s', 'x', 'y'} sage: m.codomain() Finite words over {'s', 'x', 'y'}
Specifying the domain and codomain:
sage: W = FiniteWords([0,1,2]) sage: d = {0:[0,1], 1:[0,1,0], 2:[0]} sage: m = WordMorphism(d, domain=W, codomain=W) sage: m([0]).parent() Finite words over {0, 1, 2}
When the alphabet is non-sortable, the domain and/or codomain must be explicitly given:
sage: W = FiniteWords(['a',6]) sage: d = {'a':['a',6,'a'],6:[6,6,6,'a']} sage: WordMorphism(d, domain=W, codomain=W) WordMorphism: 6->666a, a->a6a
-
abelian_rotation_subspace
()¶ Returns the subspace on which the incidence matrix of
self
acts by roots of unity.EXAMPLES:
sage: WordMorphism('0->1,1->0').abelian_rotation_subspace() Vector space of degree 2 and dimension 2 over Rational Field Basis matrix: [1 0] [0 1] sage: WordMorphism('0->01,1->10').abelian_rotation_subspace() Vector space of degree 2 and dimension 0 over Rational Field Basis matrix: [] sage: WordMorphism('0->01,1->1').abelian_rotation_subspace() Vector space of degree 2 and dimension 1 over Rational Field Basis matrix: [0 1] sage: WordMorphism('1->122,2->211').abelian_rotation_subspace() Vector space of degree 2 and dimension 1 over Rational Field Basis matrix: [ 1 -1] sage: WordMorphism('0->1,1->102,2->3,3->4,4->2').abelian_rotation_subspace() Vector space of degree 5 and dimension 3 over Rational Field Basis matrix: [0 0 1 0 0] [0 0 0 1 0] [0 0 0 0 1]
The domain needs to be equal to the codomain:
sage: WordMorphism('0->1,1->',codomain=Words('01')).abelian_rotation_subspace() Vector space of degree 2 and dimension 0 over Rational Field Basis matrix: []
-
codomain
()¶ Returns the codomain of
self
.EXAMPLES:
sage: WordMorphism('a->ab,b->a').codomain() Finite words over {'a', 'b'} sage: WordMorphism('6->ab,y->5,0->asd').codomain() Finite words over {'5', 'a', 'b', 'd', 's'}
-
conjugate
(pos)¶ Returns the morphism where the image of the letter by
self
is conjugated of parameterpos
.INPUT:
pos
- integer
EXAMPLES:
sage: m = WordMorphism('a->abcde') sage: m.conjugate(0) == m True sage: m.conjugate(1) WordMorphism: a->bcdea sage: m.conjugate(3) WordMorphism: a->deabc sage: WordMorphism('').conjugate(4) WordMorphism: sage: m = WordMorphism('a->abcde,b->xyz') sage: m.conjugate(2) WordMorphism: a->cdeab, b->zxy
-
domain
()¶ Returns domain of
self
.EXAMPLES:
sage: WordMorphism('a->ab,b->a').domain() Finite words over {'a', 'b'} sage: WordMorphism('b->ba,a->ab').domain() Finite words over {'a', 'b'} sage: WordMorphism('6->ab,y->5,0->asd').domain() Finite words over {'0', '6', 'y'}
-
dual_map
(k=1)¶ Return the dual map \(E_k^*\) of self (see [1]).
Note
It is actually implemented only for \(k=1\).
INPUT:
self
- unimodular endomorphism defined on integers1, 2, \ldots, d
k
- integer (optional, default: 1)
OUTPUT:
an instance of E1Star - the dual map
EXAMPLES:
sage: sigma = WordMorphism({1:[2],2:[3],3:[1,2]}) sage: sigma.dual_map() E_1^*(1->2, 2->3, 3->12)
sage: sigma.dual_map(k=2) Traceback (most recent call last): ... NotImplementedError: The dual map E_k^* is implemented only for k = 1 (not 2)
REFERENCES:
[1] Sano, Y., Arnoux, P. and Ito, S., Higher dimensional extensions of substitutions and their dual maps, Journal d’Analyse Mathematique 83 (2001), 183-206.
-
extend_by
(other)¶ Returns
self
extended byother
.Let \(\varphi_1:A^*\rightarrow B^*\) and \(\varphi_2:C^*\rightarrow D^*\) be two morphisms. A morphism \(\mu:(A\cup C)^*\rightarrow (B\cup D)^*\) corresponds to \(\varphi_1\) extended by \(\varphi_2\) if \(\mu(a)=\varphi_1(a)\) if \(a\in A\) and \(\mu(a)=\varphi_2(a)\) otherwise.
INPUT:
other
- a WordMorphism.
OUTPUT:
WordMorphism
EXAMPLES:
sage: m = WordMorphism('a->ab,b->ba') sage: n = WordMorphism({'0':'1','1':'0','a':'5'}) sage: m.extend_by(n) WordMorphism: 0->1, 1->0, a->ab, b->ba sage: n.extend_by(m) WordMorphism: 0->1, 1->0, a->5, b->ba sage: m.extend_by(m) WordMorphism: a->ab, b->ba
-
fixed_point
(letter)¶ Returns the fixed point of
self
beginning by the givenletter
.A fixed point of morphism \(\varphi\) is a word \(w\) such that \(\varphi(w) = w\).
INPUT:
self
- an endomorphism, must be prolongable onletter
letter
- in the domain ofself
, the first letter of the fixed point.
OUTPUT:
word
- the fixed point ofself
beginning withletter
.
EXAMPLES:
sage: W = FiniteWords('abc')
Infinite fixed point:
sage: WordMorphism('a->ab,b->ba').fixed_point(letter='a') word: abbabaabbaababbabaababbaabbabaabbaababba... sage: WordMorphism('a->ab,b->a').fixed_point(letter='a') word: abaababaabaababaababaabaababaabaababaaba... sage: WordMorphism('a->ab,b->b,c->ba', codomain=W).fixed_point(letter='a') word: abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb...
Infinite fixed point of an erasing morphism:
sage: WordMorphism('a->ab,b->,c->ba', codomain=W).fixed_point(letter='a') word: ab
Finite fixed point:
sage: WordMorphism('a->ab,b->b,c->ba', codomain=W).fixed_point(letter='b') word: b sage: _.parent() Finite words over {'a', 'b', 'c'} sage: WordMorphism('a->ab,b->cc,c->', codomain=W).fixed_point(letter='a') word: abcc sage: _.parent() Finite words over {'a', 'b', 'c'} sage: m = WordMorphism('a->abc,b->,c->') sage: fp = m.fixed_point('a'); fp word: abc sage: m = WordMorphism('a->ba,b->') sage: m('ba') word: ba sage: m.fixed_point('a') #todo: not implemented word: ba
Fixed point of a power of a morphism:
sage: m = WordMorphism('a->ba,b->ab') sage: (m^2).fixed_point(letter='a') word: abbabaabbaababbabaababbaabbabaabbaababba...
-
fixed_points
()¶ Returns the list of all fixed points of
self
.EXAMPLES:
sage: f = WordMorphism('a->ab,b->ba') sage: for w in f.fixed_points(): print(w) abbabaabbaababbabaababbaabbabaabbaababba... baababbaabbabaababbabaabbaababbaabbabaab... sage: f = WordMorphism('a->ab,b->c,c->a') sage: for w in f.fixed_points(): print(w) abcaababcabcaabcaababcaababcabcaababcabc... sage: f = WordMorphism('a->ab,b->cab,c->bcc') sage: for w in f.fixed_points(): print(w) abcabbccabcabcabbccbccabcabbccabcabbccab...
This shows that ticket trac ticket #13668 has been resolved:
sage: d = {1:[1,2],2:[2,3],3:[4],4:[5],5:[6],6:[7],7:[8],8:[9],9:[10],10:[1]} sage: s = WordMorphism(d) sage: s7 = s^7 sage: s7.fixed_points() [word: 12232342..., word: 2,3,4,5,6,7,8...] sage: s7r = s7.reversal() sage: s7r.periodic_point(2) word: 2,1,1,10,9,8,7,6,5,4,3,2,1,10,9,8,7,6,5,4,3,2,10,9,8,7,6,5,4,3,2,9,8,7,6,5,4,3,2,8,...
This shows that ticket trac ticket #13668 has been resolved:
sage: s = "1->321331332133133,2->133321331332133133,3->2133133133321331332133133" sage: s = WordMorphism(s) sage: (s^2).fixed_points() []
-
growing_letters
()¶ Returns the list of growing letters.
See
is_growing()
for more information.EXAMPLES:
sage: WordMorphism('0->01,1->10').growing_letters() ['0', '1'] sage: WordMorphism('0->01,1->1').growing_letters() ['0'] sage: WordMorphism('0->01,1->0,2->1',codomain=Words('012')).growing_letters() ['0', '1', '2']
-
has_conjugate_in_classP
(f=None)¶ Returns
True
ifself
has a conjugate in class \(f\)-\(P\).DEFINITION : Let \(A\) be an alphabet. We say that a primitive substitution \(S\) is in the class P if there exists a palindrome \(p\) and for each \(b\in A\) a palindrome \(q_b\) such that \(S(b)=pq_b\) for all \(b\in A\). [1]
Let \(f\) be an involution on \(A\). We say that a morphism \(\varphi\) is in class \(f\)-\(P\) if there exists an \(f\)-palindrome \(p\) and for each \(\alpha \in A\) there exists an \(f\)-palindrome \(q_\alpha\) such that \(\varphi(\alpha)=pq_\alpha\). [2]
INPUT:
f
- involution (default: None) on the alphabet ofself
. It must be callable on letters as well as words (e.g. WordMorphism).
REFERENCES:
[1] Hof, A., O. Knill et B. Simon, Singular continuous spectrum for palindromic Schrödinger operators, Commun. Math. Phys. 174 (1995) 149-159.
[2] Labbe, Sebastien. Proprietes combinatoires des \(f\)-palindromes, Memoire de maitrise en Mathematiques, Montreal, UQAM, 2008, 109 pages.
EXAMPLES:
sage: fibo = WordMorphism('a->ab,b->a') sage: fibo.has_conjugate_in_classP() True sage: (fibo^2).is_in_classP() False sage: (fibo^2).has_conjugate_in_classP() True
-
has_left_conjugate
()¶ Returns
True
if all the non empty images ofself
begins with the same letter.EXAMPLES:
sage: m = WordMorphism('a->abcde,b->xyz') sage: m.has_left_conjugate() False sage: WordMorphism('b->xyz').has_left_conjugate() True sage: WordMorphism('').has_left_conjugate() True sage: WordMorphism('a->,b->xyz').has_left_conjugate() True sage: WordMorphism('a->abbab,b->abb').has_left_conjugate() True sage: WordMorphism('a->abbab,b->abb,c->').has_left_conjugate() True
-
has_right_conjugate
()¶ Returns
True
if all the non empty images ofself
ends with the same letter.EXAMPLES:
sage: m = WordMorphism('a->abcde,b->xyz') sage: m.has_right_conjugate() False sage: WordMorphism('b->xyz').has_right_conjugate() True sage: WordMorphism('').has_right_conjugate() True sage: WordMorphism('a->,b->xyz').has_right_conjugate() True sage: WordMorphism('a->abbab,b->abb').has_right_conjugate() True sage: WordMorphism('a->abbab,b->abb,c->').has_right_conjugate() True
-
image
(letter)¶ Return the image of a letter.
INPUT:
letter
– a letter in the domain alphabet
OUTPUT:
word
Note
The letter is assumed to be in the domain alphabet (no check done). Hence, this method is faster than the
__call__
method suitable for words input.EXAMPLES:
sage: m = WordMorphism('a->ab,b->ac,c->a') sage: m.image('b') word: ac
sage: s = WordMorphism({('a', 1):[('a', 1), ('a', 2)], ('a', 2):[('a', 1)]}) sage: s.image(('a',1)) word: ('a', 1),('a', 2)
sage: s = WordMorphism({'b':[1,2], 'a':(2,3,4), 'z':[9,8,7]}) sage: s.image('b') word: 12 sage: s.image('a') word: 234 sage: s.image('z') word: 987
-
images
()¶ Returns the list of all the images of the letters of the alphabet under
self
.EXAMPLES:
sage: sorted(WordMorphism('a->ab,b->a').images()) [word: a, word: ab] sage: sorted(WordMorphism('6->ab,y->5,0->asd').images()) [word: 5, word: ab, word: asd]
-
incidence_matrix
()¶ Returns the incidence matrix of the morphism. The order of the rows and column are given by the order defined on the alphabet of the domain and the codomain.
The matrix returned is over the integers. If a different ring is desired, use either the
change_ring
function or thematrix
function.EXAMPLES:
sage: m = WordMorphism('a->abc,b->a,c->c') sage: m.incidence_matrix() [1 1 0] [1 0 0] [1 0 1] sage: m = WordMorphism('a->abc,b->a,c->c,d->abbccccabca,e->abc') sage: m.incidence_matrix() [1 1 0 3 1] [1 0 0 3 1] [1 0 1 5 1]
-
is_empty
()¶ Returns
True
if the cardinality of the domain is zero andFalse
otherwise.EXAMPLES:
sage: WordMorphism('').is_empty() True sage: WordMorphism('a->a').is_empty() False
-
is_endomorphism
()¶ Returns
True
if the codomain is a subset of the domain.EXAMPLES:
sage: WordMorphism('a->ab,b->a').is_endomorphism() True sage: WordMorphism('6->ab,y->5,0->asd').is_endomorphism() False sage: WordMorphism('a->a,b->aa,c->aaa').is_endomorphism() False sage: Wabc = Words('abc') sage: m = WordMorphism('a->a,b->aa,c->aaa',codomain = Wabc) sage: m.is_endomorphism() True
We check that trac ticket #8674 is fixed:
sage: P = WordPaths('abcd') sage: m = WordMorphism('a->adab,b->ab,c->cbcd,d->cd', domain=P, codomain=P) sage: m.is_endomorphism() True
-
is_erasing
()¶ Returns
True
ifself
is an erasing morphism, i.e. the image of a letter is the empty word.EXAMPLES:
sage: WordMorphism('a->ab,b->a').is_erasing() False sage: WordMorphism('6->ab,y->5,0->asd').is_erasing() False sage: WordMorphism('6->ab,y->5,0->asd,7->').is_erasing() True sage: WordMorphism('').is_erasing() False
-
is_growing
(letter=None)¶ Return
True
ifletter
is a growing letter.A letter \(a\) is growing for the morphism \(s\) if the length of the iterates of \(| s^n(a) |\) tend to infinity as \(n\) goes to infinity.
INPUT:
letter
–None
or a letter in the domain ofself
Note
If letter is
None
, this returnsTrue
ifself
is everywhere growing, i.e., all letters are growing letters (see [CassNic10]), and thatself
must be an endomorphism.EXAMPLES:
sage: WordMorphism('0->01,1->1').is_growing('0') True sage: WordMorphism('0->01,1->1').is_growing('1') False sage: WordMorphism('0->01,1->10').is_growing() True sage: WordMorphism('0->1,1->2,2->01').is_growing() True sage: WordMorphism('0->01,1->1').is_growing() False
The domain needs to be equal to the codomain:
sage: WordMorphism('0->01,1->0,2->1',codomain=Words('012')).is_growing() True
Test of erasing morphisms:
sage: WordMorphism('0->01,1->').is_growing('0') False sage: m = WordMorphism('a->bc,b->bcc,c->',codomain=Words('abc')) sage: m.is_growing('a') False sage: m.is_growing('b') False sage: m.is_growing('c') False
REFERENCES:
- CassNic10
Cassaigne J., Nicolas F. Factor complexity. Combinatorics, automata and number theory, 163–247, Encyclopedia Math. Appl., 135, Cambridge Univ. Press, Cambridge, 2010.
-
is_identity
()¶ Returns
True
ifself
is the identity morphism.EXAMPLES:
sage: m = WordMorphism('a->a,b->b,c->c,d->e') sage: m.is_identity() False sage: WordMorphism('a->a,b->b,c->c').is_identity() True sage: WordMorphism('a->a,b->b,c->cb').is_identity() False sage: m = WordMorphism('a->b,b->c,c->a') sage: (m^2).is_identity() False sage: (m^3).is_identity() True sage: (m^4).is_identity() False sage: WordMorphism('').is_identity() True sage: WordMorphism({0:[0],1:[1]}).is_identity() True
We check that trac ticket #8618 is fixed:
sage: t = WordMorphism({'a1':['a2'], 'a2':['a1']}) sage: (t*t).is_identity() True
-
is_in_classP
(f=None)¶ Returns
True
ifself
is in class \(P\) (or \(f\)-\(P\)).DEFINITION : Let \(A\) be an alphabet. We say that a primitive substitution \(S\) is in the class P if there exists a palindrome \(p\) and for each \(b\in A\) a palindrome \(q_b\) such that \(S(b)=pq_b\) for all \(b\in A\). [1]
Let \(f\) be an involution on \(A\). “We say that a morphism \(\varphi\) is in class \(f\)-\(P\) if there exists an \(f\)-palindrome \(p\) and for each \(\alpha \in A\) there exists an \(f\)-palindrome \(q_\alpha\) such that \(\varphi(\alpha)=pq_\alpha\). [2]
INPUT:
f
- involution (default: None) on the alphabet ofself
. It must be callable on letters as well as words (e.g. WordMorphism).
REFERENCES:
[1] Hof, A., O. Knill et B. Simon, Singular continuous spectrum for palindromic Schrödinger operators, Commun. Math. Phys. 174 (1995) 149-159.
[2] Labbe, Sebastien. Proprietes combinatoires des \(f\)-palindromes, Memoire de maitrise en Mathematiques, Montreal, UQAM, 2008, 109 pages.
EXAMPLES:
sage: WordMorphism('a->bbaba,b->bba').is_in_classP() True sage: tm = WordMorphism('a->ab,b->ba') sage: tm.is_in_classP() False sage: f = WordMorphism('a->b,b->a') sage: tm.is_in_classP(f=f) True sage: (tm^2).is_in_classP() True sage: (tm^2).is_in_classP(f=f) False sage: fibo = WordMorphism('a->ab,b->a') sage: fibo.is_in_classP() True sage: fibo.is_in_classP(f=f) False sage: (fibo^2).is_in_classP() False sage: f = WordMorphism('a->b,b->a,c->c') sage: WordMorphism('a->acbcc,b->acbab,c->acbba').is_in_classP(f) True
-
is_involution
()¶ Returns
True
ifself
is an involution, i.e. its square is the identity.INPUT:
self
- an endomorphism
EXAMPLES:
sage: WordMorphism('a->b,b->a').is_involution() True sage: WordMorphism('a->b,b->ba').is_involution() False sage: WordMorphism({0:[1],1:[0]}).is_involution() True
-
is_primitive
()¶ Returns
True
ifself
is primitive.A morphism \(\varphi\) is primitive if there exists an positive integer \(k\) such that for all \(\alpha\in\Sigma\), \(\varphi^k(\alpha)\) contains all the letters of \(\Sigma\).
INPUT:
self
- an endomorphism
ALGORITHM:
Exercices 8.7.8, p.281 in [1]: (c) Let \(y(M)\) be the least integer \(e\) such that \(M^e\) has all positive entries. Prove that, for all primitive matrices \(M\), we have \(y(M) \leq (d-1)^2 + 1\). (d) Prove that the bound \(y(M)\leq (d-1)^2+1\) is best possible.
EXAMPLES:
sage: tm = WordMorphism('a->ab,b->ba') sage: tm.is_primitive() True sage: fibo = WordMorphism('a->ab,b->a') sage: fibo.is_primitive() True sage: m = WordMorphism('a->bb,b->aa') sage: m.is_primitive() False sage: f = WordMorphism({0:[1],1:[0]}) sage: f.is_primitive() False
sage: s = WordMorphism('a->b,b->c,c->ab') sage: s.is_primitive() True sage: s = WordMorphism('a->b,b->c,c->d,d->e,e->f,f->g,g->h,h->ab') sage: s.is_primitive() True
REFERENCES:
[1] Jean-Paul Allouche and Jeffrey Shallit, Automatic Sequences: Theory, Applications, Generalizations, Cambridge University Press, 2003.
-
is_prolongable
(letter)¶ Returns
True
ifself
is prolongable onletter
.A morphism \(\varphi\) is prolongable on a letter \(a\) if \(a\) is a prefix of \(\varphi(a)\).
INPUT:
self
- its codomain must be an instance of Wordsletter
- a letter in the domain alphabet
OUTPUT:
Boolean
EXAMPLES:
sage: WordMorphism('a->ab,b->a').is_prolongable(letter='a') True sage: WordMorphism('a->ab,b->a').is_prolongable(letter='b') False sage: WordMorphism('a->ba,b->ab').is_prolongable(letter='b') False sage: (WordMorphism('a->ba,b->ab')^2).is_prolongable(letter='b') True sage: WordMorphism('a->ba,b->').is_prolongable(letter='b') False sage: WordMorphism('a->bb,b->aac').is_prolongable(letter='a') False
We check that trac ticket #8595 is fixed:
sage: s = WordMorphism({('a', 1) : [('a', 1), ('a', 2)], ('a', 2) : [('a', 1)]}) sage: s.is_prolongable(('a',1)) True
-
is_uniform
(k=None)¶ Returns True if self is a \(k\)-uniform morphism.
Let \(k\) be a positive integer. A morphism \(\phi\) is called \(k\)-uniform if for every letter \(\alpha\), we have \(|\phi(\alpha)| = k\). In other words, all images have length \(k\). A morphism is called uniform if it is \(k\)-uniform for some positive integer \(k\).
INPUT:
k
- a positive integer or None. If set to a positive integer, then the function return True if self is \(k\)-uniform. If set to None, then the function return True if self is uniform.
EXAMPLES:
sage: phi = WordMorphism('a->ab,b->a') sage: phi.is_uniform() False sage: phi.is_uniform(k=1) False sage: tau = WordMorphism('a->ab,b->ba') sage: tau.is_uniform() True sage: tau.is_uniform(k=1) False sage: tau.is_uniform(k=2) True
-
language
(n, u=None)¶ Return the words of length
n
in the language generated by this substitution.Given a non-erasing substitution \(s\) and a word \(u\) the DOL-language generated by \(s\) and \(u\) is the union of the factors of \(s^n(u)\) where \(n\) is a non-negative integer.
INPUT:
n
– non-negative integer - length of the words in the languageu
– a word orNone
(optional, defaultNone
) - if set toNone
some letter of the alphabet is used
OUTPUT: a Python set
EXAMPLES:
The fibonacci morphism:
sage: s = WordMorphism({0: [0,1], 1:[0]}) sage: sorted(s.language(3)) [word: 001, word: 010, word: 100, word: 101] sage: len(s.language(1000)) 1001 sage: all(len(s.language(n)) == n+1 for n in range(100)) True
A growing but non-primitive example. The DOL-languages generated by 0 and 2 are different:
sage: s = WordMorphism({0: [0,1], 1:[0], 2:[2,0,2]}) sage: u = s.fixed_point(0) sage: A0 = u[:200].factor_set(5) sage: B0 = s.language(5, [0]) sage: set(A0) == B0 True sage: v = s.fixed_point(2) sage: A2 = v[:200].factor_set(5) sage: B2 = s.language(5, [2]) sage: set(A2) == B2 True sage: len(A0), len(A2) (6, 20)
The Chacon transformation (non-primitive):
sage: s = WordMorphism({0: [0,0,1,0], 1:[1]}) sage: sorted(s.language(10)) [word: 0001000101, word: 0001010010, ... word: 1010010001, word: 1010010100]
-
latex_layout
(layout=None)¶ Get or set the actual latex layout (oneliner vs array).
INPUT:
layout
- string (default:None
), can take one of the following values:None
- Returns the actual latex layout. By default, the layout is'array'
'oneliner'
- Set the layout to'oneliner'
'array'
- Set the layout to'array'
EXAMPLES:
sage: s = WordMorphism('a->ab,b->ba') sage: s.latex_layout() 'array' sage: s.latex_layout('oneliner') sage: s.latex_layout() 'oneliner'
-
list_of_conjugates
()¶ Returns the list of all the conjugate morphisms of
self
.DEFINITION:
Recall from Lothaire [1] (Section 2.3.4) that \(\varphi\) is right conjugate of \(\varphi'\), noted \(\varphi\triangleleft\varphi'\), if there exists \(u \in \Sigma^*\) such that
\[\varphi(\alpha)u = u\varphi'(\alpha),\]for all \(\alpha \in \Sigma\), or equivalently that \(\varphi(x)u = u\varphi'(x)\), for all words \(x \in \Sigma^*\). Clearly, this relation is not symmetric so that we say that two morphisms \(\varphi\) and \(\varphi'\) are conjugate, noted \(\varphi\bowtie\varphi'\), if \(\varphi\triangleleft\varphi'\) or \(\varphi'\triangleleft\varphi\). It is easy to see that conjugacy of morphisms is an equivalence relation.
REFERENCES:
[1] M. Lothaire, Algebraic Combinatorics on words, Cambridge University Press, 2002.
EXAMPLES:
sage: m = WordMorphism('a->abbab,b->abb') sage: m.list_of_conjugates() [WordMorphism: a->babba, b->bab, WordMorphism: a->abbab, b->abb, WordMorphism: a->bbaba, b->bba, WordMorphism: a->babab, b->bab, WordMorphism: a->ababb, b->abb, WordMorphism: a->babba, b->bba, WordMorphism: a->abbab, b->bab] sage: m = WordMorphism('a->aaa,b->aa') sage: m.list_of_conjugates() [WordMorphism: a->aaa, b->aa] sage: WordMorphism('').list_of_conjugates() [WordMorphism: ] sage: m = WordMorphism('a->aba,b->aba') sage: m.list_of_conjugates() [WordMorphism: a->baa, b->baa, WordMorphism: a->aab, b->aab, WordMorphism: a->aba, b->aba] sage: m = WordMorphism('a->abb,b->abbab,c->') sage: m.list_of_conjugates() [WordMorphism: a->bab, b->babba, c->, WordMorphism: a->abb, b->abbab, c->, WordMorphism: a->bba, b->bbaba, c->, WordMorphism: a->bab, b->babab, c->, WordMorphism: a->abb, b->ababb, c->, WordMorphism: a->bba, b->babba, c->, WordMorphism: a->bab, b->abbab, c->]
-
partition_of_domain_alphabet
()¶ Returns a partition of the domain alphabet.
Let \(\varphi:\Sigma^*\rightarrow\Sigma^*\) be an involution. There exists a triple of sets \((A, B, C)\) such that
\(A \cup B \cup C =\Sigma\);
\(A\), \(B\) and \(C\) are mutually disjoint and
\(\varphi(A)= B\), \(\varphi(B)= A\), \(\varphi(C)= C\).
These sets are not unique.
INPUT:
self
- An involution.
OUTPUT:
A tuple of three sets
EXAMPLES:
sage: m = WordMorphism('a->b,b->a') sage: m.partition_of_domain_alphabet() #random ordering ({'a'}, {'b'}, {}) sage: m = WordMorphism('a->b,b->a,c->c') sage: m.partition_of_domain_alphabet() #random ordering ({'a'}, {'b'}, {'c'}) sage: m = WordMorphism('a->a,b->b,c->c') sage: m.partition_of_domain_alphabet() #random ordering ({}, {}, {'a', 'c', 'b'}) sage: m = WordMorphism('A->T,T->A,C->G,G->C') sage: m.partition_of_domain_alphabet() #random ordering ({'A', 'C'}, {'T', 'G'}, {}) sage: I = WordMorphism({0:oo,oo:0,1:-1,-1:1,2:-2,-2:2,3:-3,-3:3}) sage: I.partition_of_domain_alphabet() #random ordering ({0, -1, -3, -2}, {1, 2, 3, +Infinity}, {})
-
periodic_point
(letter)¶ Return the periodic point of self that starts with
letter
.EXAMPLES:
sage: f = WordMorphism('a->bab,b->ab') sage: f.periodic_point('a') word: abbababbababbabababbababbabababbababbaba... sage: f.fixed_point('a') Traceback (most recent call last): ... TypeError: self must be prolongable on a
-
periodic_points
()¶ Return the periodic points of
f
as a list of tuples where each tuple is a periodic orbit off
.EXAMPLES:
sage: f = WordMorphism('a->aba,b->baa') sage: for p in f.periodic_points(): ....: print("{} , {}".format(len(p), p[0])) 1 , ababaaababaaabaabaababaaababaaabaabaabab... 1 , baaabaabaababaaabaababaaabaababaaababaaa... sage: f = WordMorphism('a->bab,b->aa') sage: for p in f.periodic_points(): ....: print("{} , {}".format(len(p), p[0])) 2 , aababaaaababaababbabaababaababbabaababaa... sage: f.fixed_points() []
This shows that ticket trac ticket #13668 has been resolved:
sage: d = {1:[1,2],2:[2,3],3:[4],4:[5],5:[6],6:[7],7:[8],8:[9],9:[10],10:[1]} sage: s = WordMorphism(d) sage: s7 = s^7 sage: s7r = s7.reversal() sage: for p in s7r.periodic_points(): p [word: 1,10,9,8,7,6,5,4,3,2,10,9,8,7,6,5,4,3,2,..., word: 8765432765432654325432432322176543265432..., word: 5,4,3,2,4,3,2,3,2,2,1,4,3,2,3,2,2,1,3,2,..., word: 2,1,1,10,9,8,7,6,5,4,3,2,1,10,9,8,7,6,5,..., word: 9876543287654327654326543254324323221876..., word: 6543254324323221543243232214323221322121..., word: 3,2,2,1,2,1,1,10,9,8,7,6,5,4,3,2,2,1,1,1..., word: 10,9,8,7,6,5,4,3,2,9,8,7,6,5,4,3,2,8,7,6..., word: 7654326543254324323221654325432432322154..., word: 4,3,2,3,2,2,1,3,2,2,1,2,1,1,10,9,8,7,6,5...]
-
pisot_eigenvector_left
()¶ Returns the left eigenvector of the incidence matrix associated to the largest eigenvalue (in absolute value).
Unicity of the result is guaranteed when the multiplicity of the largest eigenvalue is one, for example when self is a Pisot irreductible substitution.
A substitution is Pisot irreducible if the characteristic polynomial of its incidence matrix is irreducible over \(\QQ\) and has all roots, except one, of modulus strictly smaller than 1.
INPUT:
self
- a Pisot irreducible substitution.
EXAMPLES:
sage: m = WordMorphism('a->aaaabbc,b->aaabbc,c->aabc') sage: matrix(m) [4 3 2] [2 2 1] [1 1 1] sage: m.pisot_eigenvector_left() (1, 0.8392867552141611?, 0.5436890126920763?)
-
pisot_eigenvector_right
()¶ Returns the right eigenvector of the incidence matrix associated to the largest eigenvalue (in absolute value).
Unicity of the result is guaranteed when the multiplicity of the largest eigenvalue is one, for example when self is a Pisot irreductible substitution.
A substitution is Pisot irreducible if the characteristic polynomial of its incidence matrix is irreducible over \(\QQ\) and has all roots, except one, of modulus strictly smaller than 1.
INPUT:
self
- a Pisot irreducible substitution.
EXAMPLES:
sage: m = WordMorphism('a->aaaabbc,b->aaabbc,c->aabc') sage: matrix(m) [4 3 2] [2 2 1] [1 1 1] sage: m.pisot_eigenvector_right() (1, 0.5436890126920763?, 0.2955977425220848?)
-
rauzy_fractal_plot
(n=None, exchange=False, eig=None, translate=None, prec=53, colormap='hsv', opacity=None, plot_origin=None, plot_basis=False, point_size=None)¶ Returns a plot of the Rauzy fractal associated with a substitution.
The substitution does not have to be irreducible. The usual definition of a Rauzy fractal requires that its dominant eigenvalue is a Pisot number but the present method doesn’t require this, allowing to plot some interesting pictures in the non-Pisot case (see the examples below).
For more details about the definition of the fractal and the projection which is used, see Section 3.1 of [1].
Plots with less than 100,000 points take a few seconds, and several millions of points can be plotted in reasonable time.
Other ways to draw Rauzy fractals (and more generally projections of paths) can be found in
sage.combinat.words.paths.FiniteWordPath_all.plot_projection()
or insage.combinat.e_one_star()
.OUTPUT:
A Graphics object.
INPUT:
n
- integer (default:None
) The number of points used to plot the fractal. Default values:1000
for a 1D fractal,50000
for a 2D fractal,10000
for a 3D fractal.exchange
- boolean (default:False
). Plot the Rauzy fractal with domain exchange.eig
- a real element ofQQbar
of degree >= 2 (default:None
). The eigenvalue used to plot the fractal. It must be an eigenvalue ofself.incidence_matrix()
. The one used by default the maximal eigenvalue ofself.incidence_matrix()
(usually a Pisot number), but for substitutions with more than 3 letters other interesting choices are sometimes possible.translate
- a list of vectors ofRR^size_alphabet
, or a dictionary from the alphabet to lists of vectors (default:None
). Plot translated copies of the fractal. This option allows to plot tilings easily. The projection used for these vectors is the same as the projection used for the canonical basis to plot the fractal. If the input is a list, all the pieces will be translated and plotted. If the input is a dictionary, each piece will be translated and plotted accordingly to the vectors associated with each letter in the dictionary. Note: by default, the Rauzy fractal placed at the origin is not plotted with thetranslate
option; the vector(0,0,...,0)
has to be added manually.prec
- integer (default:53
). The number of bits used in the floating point representations of the points of the fractal.colormap
- color map or dictionary (default:'hsv'
). It can be one of the following:string
- a coloring map. For available coloring map names type:sorted(colormaps)
dict
- a dictionary of the alphabet mapped to colors.
opacity
- a dictionary from the alphabet to the real interval [0,1] (default:None
). If none is specified, all letters are plotted with opacity1
.plot_origin
- a couple(k,c)
(default:None
). If specified, mark the origin by a point of sizek
and colorc
.plot_basis
- boolean (default:False
). Plot the projection of the canonical basis with the fractal.point_size
- float (default:None
). The size of the points used to plot the fractal.
EXAMPLES:
The Rauzy fractal of the Tribonacci substitution:
sage: s = WordMorphism('1->12,2->13,3->1') sage: s.rauzy_fractal_plot() # long time Graphics object consisting of 3 graphics primitives
The “Hokkaido” fractal. We tweak the plot using the plotting options to get a nice reusable picture, in which we mark the origin by a black dot:
sage: s = WordMorphism('a->ab,b->c,c->d,d->e,e->a') sage: G = s.rauzy_fractal_plot(n=100000, point_size=3, plot_origin=(50,"black")) # not tested sage: G.show(figsize=10, axes=false) # not tested
Another “Hokkaido” fractal and its domain exchange:
sage: s = WordMorphism({1:[2], 2:[4,3], 3:[4], 4:[5,3], 5:[6], 6:[1]}) sage: s.rauzy_fractal_plot() # not tested takes > 1 second sage: s.rauzy_fractal_plot(exchange=True) # not tested takes > 1 second
A three-dimensional Rauzy fractal:
sage: s = WordMorphism('1->12,2->13,3->14,4->1') sage: s.rauzy_fractal_plot() # not tested takes > 1 second
A one-dimensional Rauzy fractal (very scattered):
sage: s = WordMorphism('1->2122,2->1') sage: s.rauzy_fractal_plot().show(figsize=20) # not tested takes > 1 second
A high resolution plot of a complicated fractal:
sage: s = WordMorphism('1->23,2->123,3->1122233') sage: G = s.rauzy_fractal_plot(n=300000) # not tested takes > 1 second sage: G.show(axes=false, figsize=20) # not tested takes > 1 second
A nice colorful animation of a domain exchange:
sage: s = WordMorphism('1->21,2->3,3->4,4->25,5->6,6->7,7->1') sage: L = [s.rauzy_fractal_plot(), s.rauzy_fractal_plot(exchange=True)] # not tested takes > 1 second sage: animate(L, axes=false).show(delay=100) # not tested takes > 1 second
Plotting with only one color:
sage: s = WordMorphism('1->12,2->31,3->1') sage: s.rauzy_fractal_plot(colormap={'1':'black', '2':'black', '3':'black'}) # not tested takes > 1 second
Different fractals can be obtained by choosing another (non-Pisot) eigenvalue:
sage: s = WordMorphism('1->12,2->3,3->45,4->5,5->6,6->7,7->8,8->1') sage: E = s.incidence_matrix().eigenvalues() sage: x = [x for x in E if -0.8 < x < -0.7][0] sage: s.rauzy_fractal_plot() # not tested takes > 1 second sage: s.rauzy_fractal_plot(eig=x) # not tested takes > 1 second
A Pisot reducible substitution with seemingly overlapping tiles:
sage: s = WordMorphism({1:[1,2], 2:[2,3], 3:[4], 4:[5], 5:[6], 6:[7], 7:[8], 8:[9], 9:[10], 10:[1]}) sage: s.rauzy_fractal_plot() # not tested takes > 1 second
A non-Pisot reducible substitution with a strange Rauzy fractal:
sage: s = WordMorphism({1:[3,2], 2:[3,3], 3:[4], 4:[1]}) sage: s.rauzy_fractal_plot() # not tested takes > 1 second
A substitution with overlapping tiles. We use the options
colormap
andopacity
to study how the tiles overlap:sage: s = WordMorphism('1->213,2->4,3->5,4->1,5->21') sage: s.rauzy_fractal_plot() # not tested takes > 1 second sage: s.rauzy_fractal_plot(colormap={'1':'red', '4':'purple'}) # not tested takes > 1 second sage: s.rauzy_fractal_plot(opacity={'1':0.1,'2':1,'3':0.1,'4':0.1,'5':0.1}, n=150000) # not tested takes > 1 second
Funny experiments by playing with the precision of the float numbers used to plot the fractal:
sage: s = WordMorphism('1->12,2->13,3->1') sage: s.rauzy_fractal_plot(prec=6) # not tested sage: s.rauzy_fractal_plot(prec=9) # not tested sage: s.rauzy_fractal_plot(prec=15) # not tested sage: s.rauzy_fractal_plot(prec=19) # not tested sage: s.rauzy_fractal_plot(prec=25) # not tested
Using the
translate
option to plot periodic tilings:sage: s = WordMorphism('1->12,2->13,3->1') sage: s.rauzy_fractal_plot(n=10000, translate=[(0,0,0),(-1,0,1),(0,-1,1),(1,-1,0),(1,0,-1),(0,1,-1),(-1,1,0)]) # not tested takes > 1 second
sage: t = WordMorphism("a->aC,b->d,C->de,d->a,e->ab") # substitution found by Julien Bernat sage: V = [vector((0,0,1,0,-1)), vector((0,0,1,-1,0))] sage: S = set(map(tuple, [i*V[0] + j*V[1] for i in [-1,0,1] for j in [-1,0,1]])) sage: t.rauzy_fractal_plot(n=10000, translate=S, exchange=true) # not tested takes > 1 second
Using the
translate
option to plot arbitrary tilings with the fractal pieces. This can be used for example to plot the self-replicating tiling of the Rauzy fractal:sage: s = WordMorphism({1:[1,2], 2:[3], 3:[4,3], 4:[5], 5:[6], 6:[1]}) sage: s.rauzy_fractal_plot() # not tested takes > 1 second sage: D = {1:[(0,0,0,0,0,0), (0,1,0,0,0,0)], 3:[(0,0,0,0,0,0), (0,1,0,0,0,0)], 6:[(0,1,0,0,0,0)]} sage: s.rauzy_fractal_plot(n=30000, translate=D) # not tested takes > 1 second
Plot the projection of the canonical basis with the fractal:
sage: s = WordMorphism({1:[2,1], 2:[3], 3:[6,4], 4:[5,1], 5:[6], 6:[7], 7:[8], 8:[9], 9:[1]}) sage: s.rauzy_fractal_plot(plot_basis=True) # not tested takes > 1 second
REFERENCES:
[1] Valerie Berthe and Anne Siegel, Tilings associated with beta-numeration and substitutions, Integers 5 (3), 2005. http://www.integers-ejcnt.org/vol5-3.html
AUTHOR:
Timo Jolivet (2012-06-16)
-
rauzy_fractal_points
(n=None, exchange=False, eig=None, translate=None, prec=53)¶ Returns a dictionary of list of points associated with the pieces of the Rauzy fractal of
self
.INPUT:
See the method
rauzy_fractal_plot()
for a description of the options and more examples.OUTPUT:
dictionary of list of points
EXAMPLES:
The Rauzy fractal of the Tribonacci substitution and the number of points in the piece of the fractal associated with
'1'
,'2'
and'3'
are respectively:sage: s = WordMorphism('1->12,2->13,3->1') sage: D = s.rauzy_fractal_points(n=100) sage: len(D['1']) 54 sage: len(D['2']) 30 sage: len(D['3']) 16
AUTHOR:
Timo Jolivet (2012-06-16)
-
rauzy_fractal_projection
(eig=None, prec=53)¶ Returns a dictionary giving the projection of the canonical basis.
See the method
rauzy_fractal_plot()
for more details about the projection.INPUT:
eig
- a real element ofQQbar
of degree >= 2 (default:None
). The eigenvalue used for the projection. It must be an eigenvalue ofself.incidence_matrix()
. The one used by default is the maximal eigenvalue ofself.incidence_matrix()
(usually a Pisot number), but for substitutions with more than 3 letters other interesting choices are sometimes possible.prec
- integer (default:53
). The number of bits used in the floating point representations of the coordinates.
OUTPUT:
dictionary, letter -> vector, giving the projection
EXAMPLES:
The projection for the Rauzy fractal of the Tribonacci substitution is:
sage: s = WordMorphism('1->12,2->13,3->1') sage: s.rauzy_fractal_projection() {'1': (1.00000000000000, 0.000000000000000), '2': (-1.41964337760708, -0.606290729207199), '3': (-0.771844506346038, 1.11514250803994)}
AUTHOR:
Timo Jolivet (2012-06-16)
-
restrict_domain
(alphabet)¶ Returns a restriction of
self
to the given alphabet.INPUT:
alphabet
- an iterable
OUTPUT:
WordMorphism
EXAMPLES:
sage: m = WordMorphism('a->b,b->a') sage: m.restrict_domain('a') WordMorphism: a->b sage: m.restrict_domain('') WordMorphism: sage: m.restrict_domain('A') WordMorphism: sage: m.restrict_domain('Aa') WordMorphism: a->b
The input alphabet must be iterable:
sage: m.restrict_domain(66) Traceback (most recent call last): ... TypeError: 'sage.rings.integer.Integer' object is not iterable
-
reversal
()¶ Returns the reversal of
self
.EXAMPLES:
sage: WordMorphism('6->ab,y->5,0->asd').reversal() WordMorphism: 0->dsa, 6->ba, y->5 sage: WordMorphism('a->ab,b->a').reversal() WordMorphism: a->ba, b->a
-
sage.combinat.words.morphism.
get_cycles
(f, domain=None)¶ Return the cycle of the function
f
on the finite set domain. It is assumed that f is an endomorphism.INPUT:
f
- function.domain
- set (default: None) - the domain off
. If none, then tries to usef.domain()
.
EXAMPLES:
sage: from sage.combinat.words.morphism import get_cycles sage: get_cycles(lambda i: (i+1)%3, domain=[0,1,2]) [(0, 1, 2)] sage: get_cycles(lambda i: [0,0,0][i], domain=[0,1,2]) [(0,)] sage: get_cycles(lambda i: [1,1,1][i], domain=[0,1,2]) [(1,)]