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Questions about problems that entail selecting the best element from some set of available alternatives, and methods to solve them.

3 votes

Formulating a linear program s.t. only extreme point solutions are found

Perturb the vector of the objective function slightly. If you got multiple optimal solutions than this vector is orthogonal to a facet $F$ of the polytope that defines the feasible area of the LP. Not …
A.Schulz's user avatar
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14 votes
Accepted

Given a set of sets, find the smallest set(s) containing at least one element from each set

The problem is the well-known NP-complete problem Hitting Set. It is closely related to Set-Cover. The NP-completeness proof can found in the classic book of Garey and Johnson. If you want to approxi …
A.Schulz's user avatar
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7 votes
Accepted

Randomized Rounding of Solutions to Linear Programs

Of course, if you round, you have to verify that rounding preserves feasibility. Let us for example consider the relaxed VERTEX-COVER LP formulation. $$ \begin{array}{lll} \text{min} & \sum_{v\in V}c …
A.Schulz's user avatar
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7 votes
Accepted

Find maximum distance between elements given constraints on some

What you describe is a linear program. You can use the following formulation: Let $x_i$ be the $i$th element. The variables are $d_1,\ldots, d_{n-1}$, where $d_i$ denotes difference between $x_{i+1}$ …
A.Schulz's user avatar
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3 votes

Finding the required value of an algebric expression

This is classical Integer Linear Programming. You have the following problem: $$\begin{align} Ax+Bx+Cx & \to \max \\ \text{s.t} \quad x,y,z &\ge 0\\ Ax+Bx+Cx &\le T \\ x,y,z &\in \mathbb{Z}\\ \end{al …
A.Schulz's user avatar
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3 votes

Given an optimal solution to the LP, show how it can be used to construct a directed cycle w...

I traced the LP back to this article. Here you can find the answer to your question presented in Theorem 2. It might be helpful to look at the dual problem of your LP. This is analyzed in the above p …
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0 votes
Accepted

ordered uniform distribution

You can now turn your decision problem into an optimization problem. For example with the technique called parametric search. …
A.Schulz's user avatar
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15 votes

How many cookies in the cookie box? -- Tiling stars

Let me answer your question partially for the hexagram case. You can make the following tiling $\hskip1.2in$ By this you will cover 12/14=6/7 of the plane (count the triangles in the dashed quadril …
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