# Questions tagged [co.combinatorics]

Questions related to combinatorics and discrete mathematical structures

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### The tree augmentation problem, but with hyperlinks

In the (Weighted) Tree Augmentation Problem, we are given a tree $T = (V,E)$ and a set of additional edges $L$ called links with non-negative costs. Each link $\ell = (u,v)$ covers the tree edges ...
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### Multi-dimensional 0-1 Knapsack problem with a high number of dimensions

I would like to solve a multi-dimensional 0-1 Knapsack problem, by looking for approximation algorithms with constant approximation ratio if possible. Here the particularity is that the number of ...
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### A question regarding the proof of Lévy–Steinitz theorem

I have asked this question in math.stackexchange.com four days ago. I did not get any feedback, so I am asking it here. I am reading the proof of Lévy–Steinitz theorem from ON THE POWER OF LINEAR ...
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### Maximize a special monotone submodular function - is it easier?

I am looking for a way to optimize the function $f$, defined below. First, fix some positive integer $k$ and let $c_1$ and $c_2$ be non-negative vectors in $\mathbb{R}^n$. Let $g$ be an increasing ...
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### On cubic planar graphs with face boundaries of length divisible by 4

All graphs considered here are finite, simple and undirected. Let $\mathscr{G}$ denote the class of cubic plane graphs for which all face boundaries are of length divisible by four. The 3-cube $Q_3$ ...
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### Cycle decompositions of locally linear 4-regular graphs

(Preface) We consider only finite, simple, undirected graphs here. An orientation of a graph $G$ is obtained by assigning some direction to each edge of $G$. (Question starts) A graph is locally ...
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I am looking for information on the bin packing problem, where the load of each bin is not the sum of items in the bin, but some other monotone set function. For example, suppose each item $i$ has ...
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### Is arrangement-type graph on cyclic $k$-permutations of $n$ already studied?

The arrangement graph $A_{n,k}$ is the graph whose vertices are $k$-permutations of an $n$-vertex set $X$ (say, $X=\mathbb{Z}_n$) and two $k$-permutations are adjacent if they differ in exactly one ...
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### How can we compute the VC dimension of a finite class of sets?

Let $F$ be a class of subsets of a finite set $X$ of cardinality $n$. What is the complexity of computing the VC dimension of $F$? Can we do better than looping through every subset of $X$ and ...
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### Does such a bipartite graph exist?

In the course of my studies on graphs I sometimes use gadgets. I recently came upon a need for a certain bipartite graph with the following properties, and I am wondering if anyone knows if such a ...
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### Boltzmann sampling for containers/dependent polynomials?

I’d like to randomly sample from dependently-typed data structures. Has anyone looked at extending Boltzmann sampling to containers or dependent polynomials?
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### Prove that this linear relaxation has half-integral extreme points

Given a graph $G=(V,E)$, here is a Linear Relaxation of the edge cover polytope: (1) For each $v \in V, \sum_{e \in \delta(v)} x_e \geq 1.$ (2) For each $e \in E$, $0 \leq x_e \leq 1.$ Here $\delta(S)$...
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### Minimum spanning tree, but with an unusual objective function

This is a problem that came up in my study of rumour networks. I was wondering if anyone had thoughts or references on this problem. If we have a rooted tree $T = (V,E)$ with root $r$, I first label ...
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### XOR Resilient Encoding

I am looking for an efficient encoding algorithm $E:\{0,1\}^n\to\{0,1\}^m$ such that given $E(x)\oplus E(y)$ for $x\neq y$, we can reconstruct $x$ and $y$. One example of such an algorithm would be ...
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### Maximum weight matching with classes of edges in a multi-edge bipartite graph

Posted a similar question in mathoverflow, have tried to reduce this to Ford Fulkerson, but been stuck. Thought I'd ask TCS community to see if there are any ideas from individuals, here. Consider a ...
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### Subset sum for lists [closed]

Given a target list a = [2,4,1,4]` and a list of lists ...
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### Inferring the Kolmogorov complexity of a string from its substrings' complexity

I know that the Kolmogorov complexity of a substring $v$ of an incompressible string $x$ has $C(v)\geq |v|-O(\log{|x|})$ , but I'm wondering if it is also possible to infer the complexity of a string ...
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### "Parity testing set" for disjoint pairs of sets

I'd like a construction of the following description. Let $V$ be a set of $n$ elements. I'd like a collection $X$ of subsets of $V$ such that for any pair $(P,Q)$ of disjoint subsets of $V$, there ...
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### How many maximal planar graphs are there?

We denote by a triangulation a (simple) maximal planar graph. How many triangulations on $n$ vertices are there? How many triangulations are there if we cannot distinguish the vertices, i.e. ...
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### Upper bound on Independence Number of Random Regular Graph with degree $\Theta(\sqrt{|V|} \log^2 |V|)$

Let $G=(V,E)$ be a random $\Delta$-regular graph with $\Delta \in \Theta(\sqrt{|V|} \log^2 |V|)$. I'm analysing an algorithm having asymptotic running time crucially depending on the Independence ...
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### $k$-XOR collision free families

Given parameters $n,k\in \mathbb N^+$, I'm interested in finding a set of binary vectors $V_{n,k}=\{v_1,\ldots,v_n\}$ of length that satisfies: $\forall i: v_i\in\{0,1\}^{z_{n,k}}$. The bitwise xor ...
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### Damerau–Levenshtein distance with transposition of non-adjacent characters?

Wondering if it's possible to calculate Damerau–Levenshtein distance with transposition of non-adjacent characters (DL distance allows transposition of immediately adjacent characters only). I want ...
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### Is this homework problem on T-joins wrong? [closed]

In Question 9.3a, it states that if $T=V$, then the minimum cost perfect matching is the minimum cost T-join. Is this actually true? I think I have a counterexample which I have drawn below.
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### Where to find info on (polytime) approximability of various discrete optimization problems?

Where to find info on (polytime) approximability of various discrete optimization problems? Sorry if this is stupid,but is there a site or reference that keeps up to date info on approximability of ...
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### does within the "range a and b" include a and b?

I have not found the answer to this doubt of mine elsewhere, hence posting it here. It may be a silly question but I just want to be sure :P would be great if someone could help me out with this ...
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### Quantum error correction and graph codes

I was reading combinatorial approach towards quantum correction. A lot of work in this is on finding diagonal distance of a graph. Let me add definition of diagonal distance so that this remains self-...
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### Name of (and solution to) this generalization of linear assignment

I would like to know if the following problem is known and has any efficient solution. Given an $n\times n$ score matrix $S$. Find the best $a$ elements, in terms of their sum of scores, such that no ...
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### NP hard proving: separate graph into a set of the same size disjoint parts by maximizing the shared neighbours of each part

Given a graph $G=\{V,E\}$ where $V$ denotes the nodes and $E$ denotes edges. The size of the node $|V| = nk$. The target is to separte the graph into $n$ disjoint parts $P=\{V_i\}_{i=1}^n$ and the ...
Given a parameter $k$, and a graph $G$ with $O(k^2)$ vertices that has a maximum clique with $\le k$ vertices, I want to investigate the maximum number of colors $C(k)$ needed to properly color $G$, i....