Abstract word (finite or infinite)#
This module gathers functions that works for both finite and infinite words.
AUTHORS:
Sébastien Labbé
Franco Saliola
EXAMPLES:
sage: a = 0.618
sage: g = words.CodingOfRotationWord(alpha=a, beta=1-a, x=a)
sage: f = words.FibonacciWord()
sage: p = f.longest_common_prefix(g, length='finite')
sage: p
word: 0100101001001010010100100101001001010010...
sage: p.length()
231
- class sage.combinat.words.abstract_word.Word_class#
Bases:
SageObject
- apply_morphism(morphism)#
Returns the word obtained by applying the morphism to self.
INPUT:
morphism
- Can be an instance of WordMorphism, or anything that can be used to construct one.
EXAMPLES:
sage: w = Word("ab") sage: d = {'a':'ab', 'b':'ba'} sage: w.apply_morphism(d) word: abba sage: w.apply_morphism(WordMorphism(d)) word: abba
sage: w = Word('ababa') sage: d = dict(a='ab', b='ba') sage: d {'a': 'ab', 'b': 'ba'} sage: w.apply_morphism(d) word: abbaabbaab
For infinite words:
sage: t = words.ThueMorseWord([0,1]); t word: 0110100110010110100101100110100110010110... sage: t.apply_morphism({0:8,1:9}) word: 8998988998898998988989988998988998898998...
- complete_return_words_iterator(fact)#
Returns an iterator over all the complete return words of fact in self (without unicity).
A complete return words \(u\) of a factor \(v\) is a factor starting by the given factor \(v\) and ending just after the next occurrence of this factor \(v\). See for instance [1].
INPUT:
fact
- a non empty finite word
OUTPUT:
iterator
EXAMPLES:
sage: TM = words.ThueMorseWord() sage: fact = Word([0,1,1,0,1]) sage: it = TM.complete_return_words_iterator(fact) sage: next(it) word: 01101001100101101 sage: next(it) word: 01101001011001101 sage: next(it) word: 011010011001011001101 sage: next(it) word: 0110100101101 sage: next(it) word: 01101001100101101 sage: next(it) word: 01101001011001101
REFERENCES:
[1] J. Justin, L. Vuillon, Return words in Sturmian and episturmian words, Theor. Inform. Appl. 34 (2000) 343–356.
- delta()#
Returns the image of self under the delta morphism.
This is the word composed of the length of consecutive runs of the same letter in a given word.
OUTPUT:
Word over integers
EXAMPLES:
For finite words:
sage: W = Words('0123456789') sage: W('22112122').delta() word: 22112 sage: W('555008').delta() word: 321 sage: W().delta() word: sage: Word('aabbabaa').delta() word: 22112
For infinite words:
sage: t = words.ThueMorseWord() sage: t.delta() word: 1211222112112112221122211222112112112221...
- factor_occurrences_iterator(fact)#
Returns an iterator over all occurrences (including overlapping ones) of fact in self in their order of appearance.
INPUT:
fact
- a non empty finite word
OUTPUT:
iterator
EXAMPLES:
sage: TM = words.ThueMorseWord() sage: fact = Word([0,1,1,0,1]) sage: it = TM.factor_occurrences_iterator(fact) sage: next(it) 0 sage: next(it) 12 sage: next(it) 24
sage: u = Word('121') sage: w = Word('121213211213') sage: list(w.factor_occurrences_iterator(u)) [0, 2, 8]
- finite_differences(mod=None)#
Return the word obtained by the differences of consecutive letters of
self
.INPUT:
self
- A word over the integers.mod
- (default: None) It can be one of the following:None or 0 : result is over the integers
integer : result is over the integers modulo
mod
.
EXAMPLES:
sage: w = Word([x^2 for x in range(10)]) sage: w.finite_differences() word: 1,3,5,7,9,11,13,15,17 sage: w.finite_differences(mod=4) word: 131313131 sage: w.finite_differences(mod=0) word: 1,3,5,7,9,11,13,15,17
- first_occurrence(other, start=0)#
Return the position of the first occurrence of
other
inself
.If
other
is not a factor ofself
, it returnsNone
or loops forever whenself
is an infinite word.INPUT:
other
– a finite wordstart
– integer (default:0
), where the search starts
OUTPUT:
integer or
None
EXAMPLES:
sage: w = Word('01234567890123456789') sage: w.first_occurrence(Word('3456')) 3 sage: w.first_occurrence(Word('3456'), start=7) 13
When the factor is not present,
None
is returned:sage: w.first_occurrence(Word('3456'), start=17) is None True sage: w.first_occurrence(Word('3333')) is None True
Also works for searching a finite word in an infinite word:
sage: w = Word('0123456789')^oo sage: w.first_occurrence(Word('3456')) 3 sage: w.first_occurrence(Word('3456'), start=1000) 1003
But it will loop for ever if the factor is not found:
sage: w.first_occurrence(Word('3333')) # not tested -- infinite loop
The empty word occurs in a word:
sage: Word('123').first_occurrence(Word(''), 0) 0 sage: Word('').first_occurrence(Word(''), 0) 0
- is_empty()#
Returns True if the length of self is zero, and False otherwise.
EXAMPLES:
sage: it = iter([]) sage: Word(it).is_empty() True sage: it = iter([1,2,3]) sage: Word(it).is_empty() False sage: from itertools import count sage: Word(count()).is_empty() False
- is_finite()#
Returns whether this word is known to be finite.
Warning
A word defined by an iterator such that its end has never been reached will returns False.
EXAMPLES:
sage: Word([]).is_finite() True sage: Word('a').is_finite() True sage: TM = words.ThueMorseWord() sage: TM.is_finite() False
sage: w = Word(iter('a'*100)) sage: w.is_finite() False
- iterated_right_palindromic_closure(f=None, algorithm='recursive')#
Returns the iterated (\(f\)-)palindromic closure of self.
INPUT:
f
- involution (default: None) on the alphabet of self. It must be callable on letters as well as words (e.g. WordMorphism).algorithm
- string (default:'recursive'
) specifying which algorithm to be used when computing the iterated palindromic closure. It must be one of the two following values:'definition'
- computed using the definition'recursive'
- computation based on an efficient formula that recursively computes the iterated right palindromic closure without having to recompute the longest \(f\)-palindromic suffix at each iteration [2].
OUTPUT:
word – the iterated (\(f\)-)palindromic closure of self
EXAMPLES:
sage: Word('123').iterated_right_palindromic_closure() word: 1213121
sage: w = Word('abc') sage: w.iterated_right_palindromic_closure() word: abacaba
sage: w = Word('aaa') sage: w.iterated_right_palindromic_closure() word: aaa
sage: w = Word('abbab') sage: w.iterated_right_palindromic_closure() word: ababaabababaababa
A right \(f\)-palindromic closure:
sage: f = WordMorphism('a->b,b->a') sage: w = Word('abbab') sage: w.iterated_right_palindromic_closure(f=f) word: abbaabbaababbaabbaabbaababbaabbaab
An infinite word:
sage: t = words.ThueMorseWord('ab') sage: t.iterated_right_palindromic_closure() word: ababaabababaababaabababaababaabababaabab...
There are two implementations computing the iterated right \(f\)-palindromic closure, the latter being much more efficient:
sage: w = Word('abaab') sage: u = w.iterated_right_palindromic_closure(algorithm='definition') sage: v = w.iterated_right_palindromic_closure(algorithm='recursive') sage: u word: abaabaababaabaaba sage: u == v True sage: w = words.RandomWord(8) sage: u = w.iterated_right_palindromic_closure(algorithm='definition') sage: v = w.iterated_right_palindromic_closure(algorithm='recursive') sage: u == v True
REFERENCES:
[1] A. de Luca, A. De Luca, Pseudopalindrome closure operators in free monoids, Theoret. Comput. Sci. 362 (2006) 282–300.
[2] J. Justin, Episturmian morphisms and a Galois theorem on continued fractions, RAIRO Theoret. Informatics Appl. 39 (2005) 207-215.
- length()#
Returns the length of self.
- lex_greater(other)#
Returns True if self is lexicographically greater than other.
EXAMPLES:
sage: w = Word([1,2,3]) sage: u = Word([1,3,2]) sage: v = Word([3,2,1]) sage: w.lex_greater(u) False sage: v.lex_greater(w) True sage: a = Word("abba") sage: b = Word("abbb") sage: a.lex_greater(b) False sage: b.lex_greater(a) True
For infinite words:
sage: t = words.ThueMorseWord() sage: t[:10].lex_greater(t) False sage: t.lex_greater(t[:10]) True
- lex_less(other)#
Returns True if self is lexicographically less than other.
EXAMPLES:
sage: w = Word([1,2,3]) sage: u = Word([1,3,2]) sage: v = Word([3,2,1]) sage: w.lex_less(u) True sage: v.lex_less(w) False sage: a = Word("abba") sage: b = Word("abbb") sage: a.lex_less(b) True sage: b.lex_less(a) False
For infinite words:
sage: t = words.ThueMorseWord() sage: t.lex_less(t[:10]) False sage: t[:10].lex_less(t) True
- longest_common_prefix(other, length='unknown')#
Returns the longest common prefix of self and other.
INPUT:
other
- wordlength
- string (optional, default:'unknown'
) the length type of the resulting word if known. It may be one of the following:'unknown'
'finite'
'infinite'
EXAMPLES:
sage: f = lambda n : add(Integer(n).digits(2)) % 2 sage: t = Word(f) sage: u = t[:10] sage: t.longest_common_prefix(u) word: 0110100110
The longest common prefix of two equal infinite words:
sage: t1 = Word(f) sage: t2 = Word(f) sage: t1.longest_common_prefix(t2) word: 0110100110010110100101100110100110010110...
Useful to study the approximation of an infinite word:
sage: a = 0.618 sage: g = words.CodingOfRotationWord(alpha=a, beta=1-a, x=a) sage: f = words.FibonacciWord() sage: p = f.longest_common_prefix(g, length='finite') sage: p.length() 231
- longest_periodic_prefix(period=1)#
Returns the longest prefix of self having the given period.
INPUT:
period
- positive integer (optional, default 1)
OUTPUT:
word
EXAMPLES:
sage: Word([]).longest_periodic_prefix() word: sage: Word([1]).longest_periodic_prefix() word: 1 sage: Word([1,2]).longest_periodic_prefix() word: 1 sage: Word([1,1,2]).longest_periodic_prefix() word: 11 sage: Word([1,2,1,2,1,3]).longest_periodic_prefix(2) word: 12121 sage: type(_) <class 'sage.combinat.words.word.FiniteWord_iter_with_caching'> sage: Word(lambda n:0).longest_periodic_prefix() word: 0000000000000000000000000000000000000000...
- palindrome_prefixes_iterator(max_length=None)#
Returns an iterator over the palindrome prefixes of self.
INPUT:
max_length
- non negative integer or None (optional, default: None) the maximum length of the prefixes
OUTPUT:
iterator
EXAMPLES:
sage: w = Word('abaaba') sage: for pp in w.palindrome_prefixes_iterator(): pp word: word: a word: aba word: abaaba sage: for pp in w.palindrome_prefixes_iterator(max_length=4): pp word: word: a word: aba
You can iterate over the palindrome prefixes of an infinite word:
sage: f = words.FibonacciWord() sage: for pp in f.palindrome_prefixes_iterator(max_length=20): pp word: word: 0 word: 010 word: 010010 word: 01001010010 word: 0100101001001010010
- parent()#
Returns the parent of self.
- partial_sums(start, mod=None)#
Returns the word defined by the partial sums of its prefixes.
INPUT:
self
- A word over the integers.start
- integer, the first letter of the resulting word.mod
- (default: None) It can be one of the following:None or 0 : result is over the integers
integer : result is over the integers modulo
mod
.
EXAMPLES:
sage: w = Word(range(10)) sage: w.partial_sums(0) word: 0,0,1,3,6,10,15,21,28,36,45 sage: w.partial_sums(1) word: 1,1,2,4,7,11,16,22,29,37,46
sage: w = Word([1,2,3,1,2,3,2,2,2,2]) sage: w.partial_sums(0, mod=None) word: 0,1,3,6,7,9,12,14,16,18,20 sage: w.partial_sums(0, mod=0) word: 0,1,3,6,7,9,12,14,16,18,20 sage: w.partial_sums(0, mod=8) word: 01367146024 sage: w.partial_sums(0, mod=4) word: 01323102020 sage: w.partial_sums(0, mod=2) word: 01101100000 sage: w.partial_sums(0, mod=1) word: 00000000000
- prefixes_iterator(max_length=None)#
Returns an iterator over the prefixes of self.
INPUT:
max_length
- non negative integer or None (optional, default: None) the maximum length of the prefixes
OUTPUT:
iterator
EXAMPLES:
sage: w = Word('abaaba') sage: for p in w.prefixes_iterator(): p word: word: a word: ab word: aba word: abaa word: abaab word: abaaba sage: for p in w.prefixes_iterator(max_length=3): p word: word: a word: ab word: aba
You can iterate over the prefixes of an infinite word:
sage: f = words.FibonacciWord() sage: for p in f.prefixes_iterator(max_length=8): p word: word: 0 word: 01 word: 010 word: 0100 word: 01001 word: 010010 word: 0100101 word: 01001010
- return_words_iterator(fact)#
Returns an iterator over all the return words of fact in self (without unicity).
INPUT:
fact
- a non empty finite word
OUTPUT:
iterator
EXAMPLES:
sage: w = Word('baccabccbacbca') sage: b = Word('b') sage: list(w.return_words_iterator(b)) [word: bacca, word: bcc, word: bac]
sage: TM = words.ThueMorseWord() sage: fact = Word([0,1,1,0,1]) sage: it = TM.return_words_iterator(fact) sage: next(it) word: 011010011001 sage: next(it) word: 011010010110 sage: next(it) word: 0110100110010110 sage: next(it) word: 01101001 sage: next(it) word: 011010011001 sage: next(it) word: 011010010110
- string_rep()#
Returns the (truncated) raw sequence of letters as a string.
EXAMPLES:
sage: Word('abbabaab').string_rep() 'abbabaab' sage: Word([0, 1, 0, 0, 1]).string_rep() '01001' sage: Word([0,1,10,101]).string_rep() '0,1,10,101' sage: WordOptions(letter_separator='-') sage: Word([0,1,10,101]).string_rep() '0-1-10-101' sage: WordOptions(letter_separator=',')
- sum_digits(base=2, mod=None)#
Return the sequence of the sum modulo
mod
of the digits written in basebase
ofself
.INPUT:
self
- word over natural numbersbase
- integer (default : 2), greater or equal to 2mod
- modulo (default:None
), can take the following values:integer – the modulo
None
- the valuebase
is considered for the modulo.
EXAMPLES:
The Thue-Morse word:
sage: from itertools import count sage: Word(count()).sum_digits() word: 0110100110010110100101100110100110010110...
Sum of digits modulo 2 of the prime numbers written in base 2:
sage: Word(primes(1000)).sum_digits() # optional - sage.libs.pari word: 1001110100111010111011001011101110011011...
Sum of digits modulo 3 of the prime numbers written in base 3:
sage: Word(primes(1000)).sum_digits(base=3) # optional - sage.libs.pari word: 2100002020002221222121022221022122111022... sage: Word(primes(1000)).sum_digits(base=3, mod=3) # optional - sage.libs.pari word: 2100002020002221222121022221022122111022...
Sum of digits modulo 2 of the prime numbers written in base 3:
sage: Word(primes(1000)).sum_digits(base=3, mod=2) # optional - sage.libs.pari word: 0111111111111111111111111111111111111111...
Sum of digits modulo 7 of the prime numbers written in base 10:
sage: Word(primes(1000)).sum_digits(base=10, mod=7) # optional - sage.libs.pari word: 2350241354435041006132432241353546006304...
Negative entries:
sage: w = Word([-1,0,1,2,3,4,5]) sage: w.sum_digits() Traceback (most recent call last): ... NotImplementedError: nth digit of Thue-Morse word is not implemented for negative value of n
- to_integer_word()#
Returns a word over the integers whose letters are those output by self._to_integer_iterator()
EXAMPLES:
sage: from itertools import count sage: w = Word(count()); w word: 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,... sage: w.to_integer_word() word: 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,... sage: w = Word(iter("abbacabba"), length="finite"); w word: abbacabba sage: w.to_integer_word() word: 011020110 sage: w = Word(iter("abbacabba"), length="unknown"); w word: abbacabba sage: w.to_integer_word() word: 011020110