Python Permutation.to_cycles方法代码示例

# 需要导入模块: from sage.combinat.permutation import Permutation [as 别名]
# 或者: from sage.combinat.permutation.Permutation import to_cycles [as 别名]
    def __classcall_private__(cls, p):
        r"""
        This function tries to recognize the input (it can be either a list or
        a tuple of pairs, or a fix-point free involution given as a list or as
        a permutation), constructs the parent (enumerated set of
        PerfectMatchings of the ground set) and calls the __init__ function to
        construct our object.

        EXAMPLES::

            sage: m = PerfectMatching([('a','e'),('b','c'),('d','f')]);m
            [('a', 'e'), ('b', 'c'), ('d', 'f')]
            sage: isinstance(m,PerfectMatching)
            True
            sage: n = PerfectMatching([3, 8, 1, 7, 6, 5, 4, 2]);n
            [(1, 3), (2, 8), (4, 7), (5, 6)]
            sage: n.parent()
            Set of perfect matchings of {1, 2, 3, 4, 5, 6, 7, 8}
            sage: PerfectMatching([(1, 4), (2, 3), (5, 6)]).is_non_crossing()
            True

        The function checks that the given list or permutation is a valid perfect
        matching (i.e. a list of pairs with pairwise disjoint elements  or a
        fixpoint-free involution) and raises a ValueError otherwise:

            sage: PerfectMatching([(1, 2, 3), (4, 5)])
            Traceback (most recent call last):
            ...
            ValueError: [(1, 2, 3), (4, 5)] is not a valid perfect matching: all elements of the list must be pairs

        If you know your datas are in a good format, use directly
        ``PerfectMatchings(objects)(data)``.

        TESTS::

             sage: m = PerfectMatching([('a','e'),('b','c'),('d','f')])
             sage: TestSuite(m).run()
             sage: m = PerfectMatching([])
             sage: TestSuite(m).run()
             sage: PerfectMatching(6)
             Traceback (most recent call last):
             ...
             ValueError: cannot convert p (= 6) to a PerfectMatching
             sage: PerfectMatching([(1,2,3)])
             Traceback (most recent call last):
             ...
             ValueError: [(1, 2, 3)] is not a valid perfect matching:
             all elements of the list must be pairs
             sage: PerfectMatching([(1,1)])
             Traceback (most recent call last):
             ...
             ValueError: [(1, 1)] is not a valid perfect matching:
             there are some repetitions
             sage: PerfectMatching(Permutation([4,2,1,3]))
             Traceback (most recent call last):
             ...
             ValueError: The permutation p (= [4, 2, 1, 3]) is not a fixed point free involution
        """
        # we have to extract from the argument p the set of objects of the
        # matching and the list of pairs.
        # First case: p is a list (resp tuple) of lists (resp tuple).
        if (isinstance(p, list) or isinstance(p, tuple)) and (
                all([isinstance(x, list) or isinstance(x, tuple) for x in p])):
            objects = Set(flatten(p))
            data = (map(tuple, p))
            #check if the data are correct
            if not all([len(t) == 2 for t in data]):
                raise ValueError("%s is not a valid perfect matching:\n"
                                 "all elements of the list must be pairs" % p)
            if len(objects) < 2*len(data):
                raise ValueError("%s is not a valid perfect matching:\n"
                                 "there are some repetitions" % p)
        # Second case: p is a permutation or a list of integers, we have to
        # check if it is a fix-point-free involution.
        elif ((isinstance(p, list) and
               all(map(lambda x: (isinstance(x, Integer) or isinstance(x, int)), p)))
              or isinstance(p, Permutation)):
            p = Permutation(p)
            n = len(p)
            if not(p.cycle_type() == [2 for i in range(n//2)]):
                raise ValueError("The permutation p (= %s) is not a "
                                 "fixed point free involution" % p)
            objects = Set(range(1, n+1))
            data = p.to_cycles()
        # Third case: p is already a perfect matching, we return p directly
        elif isinstance(p, PerfectMatching):
            return p
        else:
            raise ValueError("cannot convert p (= %s) to a PerfectMatching" % p)
        # Finally, we create the parent and the element using the element
        # class of the parent. Note: as this function is private, when we
        # create an object via parent.element_class(...), __init__ is directly
        # executed and we do not have an infinite loop.
        return PerfectMatchings(objects)(data)

# 需要导入模块: from sage.combinat.permutation import Permutation [as 别名]
# 或者: from sage.combinat.permutation.Permutation import to_cycles [as 别名]
    def __classcall_private__(cls, parts):
        """
        Create a perfect matching from ``parts`` with the appropriate parent.

        This function tries to recognize the input (it can be either a list or
        a tuple of pairs, or a fix-point free involution given as a list or as
        a permutation), constructs the parent (enumerated set of
        PerfectMatchings of the ground set) and calls the __init__ function to
        construct our object.

        EXAMPLES::

            sage: m = PerfectMatching([('a','e'),('b','c'),('d','f')]);m
            [('a', 'e'), ('b', 'c'), ('d', 'f')]
            sage: isinstance(m, PerfectMatching)
            True
            sage: n = PerfectMatching([3, 8, 1, 7, 6, 5, 4, 2]);n
            [(1, 3), (2, 8), (4, 7), (5, 6)]
            sage: n.parent()
            Perfect matchings of {1, 2, 3, 4, 5, 6, 7, 8}
            sage: PerfectMatching([(1, 4), (2, 3), (5, 6)]).is_noncrossing()
            True

        The function checks that the given list or permutation is
        a valid perfect matching (i.e. a list of pairs with pairwise
        disjoint elements or a fix point free involution) and raises
        a ``ValueError`` otherwise::

            sage: PerfectMatching([(1, 2, 3), (4, 5)])
            Traceback (most recent call last):
            ...
            ValueError: [(1, 2, 3), (4, 5)] is not an element of
             Perfect matchings of {1, 2, 3, 4, 5}

        TESTS::

            sage: m = PerfectMatching([('a','e'),('b','c'),('d','f')])
            sage: TestSuite(m).run()
            sage: m = PerfectMatching([])
            sage: TestSuite(m).run()
            sage: PerfectMatching(6)
            Traceback (most recent call last):
            ...
            TypeError: 'sage.rings.integer.Integer' object is not iterable
            sage: PerfectMatching([(1,2,3)])
            Traceback (most recent call last):
            ...
            ValueError: [(1, 2, 3)] is not an element of
             Perfect matchings of {1, 2, 3}

            sage: PerfectMatching([(1,1)])
            Traceback (most recent call last):
            ...
            ValueError: [(1)] is not an element of Perfect matchings of {1}

            sage: PerfectMatching(Permutation([4,2,1,3]))
            Traceback (most recent call last):
            ...
            ValueError: permutation p (= [4, 2, 1, 3]) is not a
             fixed point free involution
        """
        if ((isinstance(parts, list) and
             all((isinstance(x, (int, Integer)) for x in parts)))
            or isinstance(parts, Permutation)):
            s = Permutation(parts)
            if not all(e == 2 for e in s.cycle_type()):
                raise ValueError("permutation p (= {}) is not a "
                                 "fixed point free involution".format(s))
            parts = s.to_cycles()

        base_set = frozenset(e for p in parts for e in p)
        P = PerfectMatchings(base_set)
        return P(parts)