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Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.
0
votes
Union of Permutations
You could look for a sequence of permutations, that are adjacent in the Steinhaus-Johnson-Trotter sequence of permutations
http://en.wikipedia.org/wiki/Steinhaus%E2%80%93Johnson%E2%80%93Trotter_algori …
1
vote
Resolution of multiple edges
For the algorithmic solution, i.e. reducing the problem to an ordinary matching problem, the following idea helps:
every of the $k$ girls has bucket with $n$ balls and every girl also has $n$ empt …
1
vote
Resolution of multiple edges
One aspect of exhanging the balls a girl initially has with balls from other girls can be interpreted as an assignment problem, namely matching the balls a girl has with the colors (depicted as square …
1
vote
Algorithm for Low Discrepancy Sequence of Hamilton Cycles in Complete Graphs
Motivated by a recent upvote, I started to reconsider the problem.
The first thing I did, was to repeat my search for algorithms that generate the $n$-th Steinhaus-Trotter-Johnson permutation - needle …
1
vote
Alternative parallel paths
the answer is yes, simply because there are at least two different paths for $n\ge 2$.
Assuming that at least two different paths exist for $n\ge 2$ one can interpret the 1st path as a $0$bit and the …
1
vote
0
answers
222
views
Number of pairs of edge-disjoint Hamilton cycles in complete graphs
Question:
how many pairs $\lbrace H_i, H_j\rbrace$ of edge-disjoint Hamilton cycles are in the complete graph $K_n$ with $n$ vertices?
while I could find information to the maximal number of edge-disj …
1
vote
0
answers
73
views
TSP: Approximation Ratio of the Double Tree Heuristic after Diagonals have been Removed
In their article "Double-Tree Approximations for the Metric TSP: Is the Best One Good Enough?", Vladimir Deineko and Alexander Tiskin derive a lower bound for the approximation ratio of the double-tre …
3
votes
0
answers
217
views
Gray Code for Combinations
Question:
are Gray Codes known for enumerating all fixed-size subsets of a given finite set?
Background of the question is trying to find the lightest k-clique in a symmetric TSP instance of s …
2
votes
2
answers
265
views
Clique Size in "Triangle Regular" Graphs
Let $G(V,E)$ be a connected, simple and undirected graph with the additional constraint, that each edge is contained in the same number $k_T$ of triangles; i.e. that $G$ is regular w.r.t. to that numb …
0
votes
1
answer
79
views
Number of order-relational different weighted $K_4$
Weighted $K_4$ are the simplest non-trivial symmetric TSP instances that already exhibit a rich variety of properties, e.g. that the shortest edge is not contained in the optimal solution or that the …
3
votes
2
answers
2k
views
Invariants of Matrix Reordering
are there any invariants of matrices, that are not affected by row- and/or column permutations?
To me it seems that the sequence of singular values could be such an invariant; am I right, resp. are t …
6
votes
1
answer
361
views
Algorithm for Low Discrepancy Sequence of Hamilton Cycles in Complete Graphs
Are there deterministic algorithms that generate a sequence of Hamilton Tours that is superior to a sequence of randomly chosen tours, when applied to the TSP (by applying to the TSP, I understand sum …
1
vote
0
answers
21
views
Properties of Optimal k-Tour Spanners
Let the edge set of a Optimal k-Tour Spanner of a graph $G$ be equal to the edges of $G$ that lie on at least one optimal tour through exactly $3<k<n$ distinct vertices of $G$.
I would like to know …
1
vote
0
answers
39
views
Colorful Neighborhoods
Given:
$G:=\{V= \{v_1,\ ...\ v_n\},E\subset V\times V\}, n<\infty$, a symmetric complete, simple graph
$w:=\ \ E \ni e_{ij}\mapsto \mathbb{R}^+$, a weight function for the edges of $G$
$K:=\{c_1,\ ... …
3
votes
1
answer
144
views
"Hypo" and "Hyper" for Perfect Matching
There is a fairly rich classification on graphs with respect to the existence of Hamiltonian cycles either in unmodified graphs or after certain small modifications.
Do there also exist such classi …