def unrank_gray(self, rank, superset):
"""
Gets the Gray code ordered subset of the specified rank.
Examples:
>>> from sympy.combinatorics.subsets import Subset
>>> Subset.unrank_gray(4, ['a','b','c']).subset
['a', 'b']
>>> Subset.unrank_gray(0, ['a','b','c']).subset
[]
"""
graycode_bitlist = GrayCode.unrank(len(superset), rank)
return Subset.subset_from_bitlist(superset, graycode_bitlist)
def unrank_gray(self, rank, superset):
"""
Gets the Gray code ordered subset of the specified rank.
Examples
========
>>> from sympy.combinatorics.subsets import Subset
>>> Subset.unrank_gray(4, ['a','b','c']).subset
['a', 'b']
>>> Subset.unrank_gray(0, ['a','b','c']).subset
[]
"""
graycode_bitlist = GrayCode.unrank(len(superset), rank)
return Subset.subset_from_bitlist(superset, graycode_bitlist)
def iterate_graycode(self, k):
"""
Helper function used for prev_gray and next_gray.
It performs k step overs to get the respective Gray codes.
Examples:
>>> from sympy.combinatorics.subsets import Subset
>>> a = Subset([1,2,3], [1,2,3,4])
>>> a.iterate_graycode(3).subset
[1, 4]
>>> a.iterate_graycode(-2).subset
[1, 2, 4]
"""
unranked_code = GrayCode.unrank(self.superset_size, (self.rank_gray + k) % self.cardinality)
return Subset.subset_from_bitlist(self.superset, unranked_code)
def iterate_graycode(self, k):
"""
Helper function used for prev_gray and next_gray.
It performs k step overs to get the respective Gray codes.
Examples
========
>>> from sympy.combinatorics.subsets import Subset
>>> a = Subset([1,2,3], [1,2,3,4])
>>> a.iterate_graycode(3).subset
[1, 4]
>>> a.iterate_graycode(-2).subset
[1, 2, 4]
"""
unranked_code = GrayCode.unrank(
self.superset_size, (self.rank_gray + k) % self.cardinality)
return Subset.subset_from_bitlist(self.superset, unranked_code)
