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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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
  • 13.2k
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 …
Manfred Weis's user avatar
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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,\ ... …
Manfred Weis's user avatar
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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 …
Manfred Weis's user avatar
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