# Tagged Questions

**3**

votes

**2**answers

169 views

### Generalized Moore Graphs

A generalized Moore graph - as defined by Cerf, Cowan, Mullin and Stanton - is one for which the girth G and diameter D satisfy G ≥ 2D - 1. These graphs retain many of the optimal properties of Moore ...

**1**

vote

**0**answers

282 views

### A detail in the proof of the Motzkin-Straus theorem

The Motzkin-Straus theorem says that the global optimum of the quadratic program
$$\max f(x)=\frac{1}{2} x^{t}Ax,\qquad \mbox{ subject to }\sum x_{i}=1 \mbox{ and } x_{i}\geq 0,$$ where $A$ is the ...

**2**

votes

**0**answers

85 views

### A Conjecture related to minimization of product of determinants over permutations

Hi
I have the following problem (and a conjecture which holds in Matlab).
Given an $N\times N$ matrix $H$, represent it by its $2N\times 2N$ real-valued representation (which I will also denote by ...

**3**

votes

**0**answers

100 views

### Multiple Number Partitioning / “Multiprocessor Scheduling”

Consider the well-known Number Partitioning / "Multiprocessor Scheduling Problem": You want to partition a set $S$ of objects (jobs) $i$ with weights $w_i$ (process time) into subsets $S_k$ (e.g. ...

**2**

votes

**1**answer

197 views

### An optimization problem, non complete bipartite graph and hungarian algorithm

I have two tables at my disposal, one work dataset and one reference dataset. Each dataset has got two columns, lets say these are fields A and B. I would like the rows in reference dataset with the ...

**1**

vote

**3**answers

1k views

### How to get the largest subset of a set of sets of intervals with no overlapping intervals

Given: Set of Set of Intervals. Example {{(1,2), (3,4)}, {(1, 3)}, {(13,14)}}
Wanted Result: Largest Subset, in which no Interval overlaps with another from every Set pairwise.
Example:
Input ...

**4**

votes

**1**answer

231 views

### An optimization involving (random) graphs

Suppose we have a graph on $n$ nodes. We would like to assign to each node either a $+1$ or a $-1$. Call this a configuration $\sigma \in \{+1,-1\}^n$. The number of $+1$s that we have to assign is ...

**8**

votes

**1**answer

197 views

### Algorithm for matching in the power set lattice

Suppose that we have two probability distributions, $f$ and $g$ on the subsets of a finite set $X$, i.e. $f, g: P(X) \to [0,1]$, with
$$
\sum_{A \subseteq X} f(A) = \sum_{A \subseteq X} g(A) = 1.
$$
...

**3**

votes

**1**answer

185 views

### Integral of a quadratic on a polygon (variations of discrete surfaces)

This question is pretty simple to state: given two linear functions on a polygon, I'm looking for a formula for the integral of their product which depends only on the values at the (unlabelled) edges ...

**4**

votes

**1**answer

442 views

### An optimization problem involving sum of binomial coefficients upto some value

I would like to minimize $f(s, n, \epsilon)$ with respect to $s$ where
$$f(s,n,\epsilon) = \left( 1 + \frac{n}{2^s} \right)\frac{1}{s} \sum_{k=0}^{\lfloor s\epsilon \rfloor} {s \choose k}~.$$
Note ...

**1**

vote

**0**answers

117 views

### Minimizing an entropylike expression with a quadratic constraint

Let '$\{X_i\}$' be a set of n positive integers, and fix k to be a positive integer. I am interested in finding the set of solutions to the pair of inequalities:
'$\displaystyle \sum_{i=1}^n X_i ...

**0**

votes

**0**answers

412 views

### Decomposing max-convolution of sum of functions ?

Hello.
$R, F_1, F_2, F_3$ are random (not-convex, not-concave) 2D matrices of size 100x100.
$R$ is a linear combination of $F_1, F_2, F_3$.
Explicitly, $R = w_1 F_1 + w_2 F_2 + w_3 F_3$
where ...

**2**

votes

**1**answer

251 views

### Maximum-bend TSP

I've seen minimum-bend TSP studied, has anyone looked at max-bend TSP?
As a special case, I'm interested in the maximum number of turns a hamiltonian path can take in an $n \times n$ square grid.
I ...

**3**

votes

**2**answers

486 views

### Cubic graphs which are “difficult to navigate”

Suppose I am inside a finite, weighted cubic graph without loops, with no information regarding its layout, including the number of vertices or distances to the adjacent vertices. I want to reach a ...

**1**

vote

**2**answers

1k views

### Greedy approach to 0-1 Knapsack problem in specific instances

The 0-1 knapsack problem is known to be NP-complete, and the greedy approach by Dantzig (based on choosing on the basis of density or value/weight) can be shown to be suboptimal using counterexamples. ...

**1**

vote

**1**answer

483 views

### Split sum into equal terms

Given a sum of $l$ integers $r_1+...+r_k+...+r_l$ and an integer $t$.
Find indices
$1 < p_1 <...< p_h <...< p_{t-1} < l$
such that in sum
...

**4**

votes

**0**answers

177 views

### restricting “dances of minimal cost” (optimization on braids/permutations?)

Consider applying the permutation (1,3,0,5,2,7,4,6) to the integers (0,1,2,3,4,5,6,7) three times.
I call this a "dance of minimal cost" because all unordered pairs in {0..7} meet each other, and the
...

**3**

votes

**2**answers

2k views

### Maximum flow with negative capacities?

I'm trying to compute an (s-t) maximum flow through a network which includes a number of arc pairs ((u,v), (v,u)) that have equal, negative capacities (weights). I'm not aware of any efficient ...

**2**

votes

**2**answers

557 views

### Mean curvature of polyhedral surfaces

Whilst working on this problem, I've come across the work of Konrad Polthier on generalizing the notion of curature to discrete surfaces; much of his work is covered in his thesis, "Polyhedral ...

**8**

votes

**2**answers

647 views

### Covering a random graph with spanning trees.

Let $G=(V,E)$ be a connected graph, say $V=\{1,\ldots,n\}$. Let $F=(V,E')$ be a uniformly random forest in $G$. (In other words, $E'$ is a subset of edges $E$ not containing a cycle, and it is ...

**27**

votes

**0**answers

2k views

### A Combinatorial Abstraction for The “Polynomial Hirsch Conjecture”

Consider $t$ disjoint families of subsets of {1,2,…,n}, ${\cal F}_1,{\cal F_2},\dots {\cal F_t}$ .
Suppose that
(*)
For every $i \lt j \lt k$
and every $R \in {\cal F}_i$, and $T \in {\cal F}_k$, ...

**-1**

votes

**2**answers

712 views

### dynamic programming and combinatorics

Suppose there are $ K $ buckets each can be filled upto $ N-1 $ balls. The gain on putting $ i $ balls in the $ k^{th} $ bucket is given by $ \Delta l_{k,i}, \, i \in [1,N-1] $. The problem is to ...

**1**

vote

**0**answers

366 views

### Minimizing quadratic form over permutations

Let $Q$ be an $n \times n$ real symmetric matrix and $x$ an $n \times 1$ real vector. Consider the following minimization problem:
$\min_{\pi \in S_n} ~(\pi x)^{\rm T} Q (\pi x)$,
where $S_n$ ...

**5**

votes

**1**answer

366 views

### How to optimize student happiness in group work?

There are $n$ students in a class, and they must be divided into, say, $k$ groups. Each student ranks the other students in order of preference of working together. Is there a way to generally ...

**5**

votes

**3**answers

604 views

### How can I embed an N-points metric space to a hypercube with low distortion?

I have a N-point metric space defined by the pairwise distance matrix. I want to encode these N points with binary strings, i.e. each point will be mapped to a vertex in a hypercube. The lengths of ...

**11**

votes

**6**answers

3k views

### Solving NP problems in (usually) Polynomial time?

Just because a problem is NP-complete doesn't mean it can't be usually solved quickly.
The best example of this is probably the traveling salesman problem, for which extraordinarily large instances ...

**1**

vote

**0**answers

120 views

### Term to describe how much harder an optimization problem can become after constraining a small part of the domain?

This is a follow up to this question.
I'm interested in discrete optimization problems formulated as 0-1 integer programs; essentially, anything of the form
$$\Phi = \max_{\mathbf{x} \in ...

**3**

votes

**2**answers

272 views

### Hardness of combinatorial optimization after adding one constraint

I'm interested generally in discrete optimization problems formulated as 0-1 integer programs; essentially, anything of the form
$$\Phi = \max_{\mathbf{x} \in \left\{0,1\right\} ^N} f(\mathbf{x})$$
...