Questions tagged [linear-programming]

Questions on linear programming, the optimization of a linear function subject to linear constraints.

A linear programming problem may be defined as the problem of maximizing or minimizing a linear function subject to linear constraints. The constraints may be equalities or inequalities.

Linear programs are problems that can be expressed in canonical form as \begin{align}\max\quad&c^\top x\\\text{s.t.}\quad& Ax\le b\\\quad& x\ge 0\end{align} where $x$ represents the vector of variables (to be determined), $c$ and $b$ are vectors of (known) coefficients, $A$ is a (known) matrix of coefficients, and ${\displaystyle (\cdot )^{\top}}$ is the matrix transpose.

The expression to be maximized or minimized is called the objective function ($c^{\top}x$ in this case).

The inequalities $Ax \le b$ and $x \ge 0$ are the constraints which specify a convex polytope over which the objective function is to be optimized. The inequality $x \ge 0$ is called non-negativity constraints and are often found in linear programming problems. The other inequality $Ax \le b$ is called the main constraints.

Applications:

Linear programming can be applied to various fields of study. It is widely used in mathematics, and to a lesser extent in business, economics, and for some engineering problems. Industries that use linear programming models include transportation, energy, telecommunications, and manufacturing. It has proven useful in modeling diverse types of problems in planning, routing, scheduling, assignment, and design.

References:

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Solving a linear problem using complementary slackness condition

Question $\max \space\space z= 8x_1 + 6x_2 -10x_3+20x_4+2x_5$ $\text{s.t.}\space\space\space\space\space 2x_1+x_2-x_3+2x_4+x_5= 25$ $\space\space\space\space\space\space\space\space\space\space 2x_1+2x_3 -x_4+3x_5= 20$ The optimal solution…
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How to find all basic feasible solutions of a linear system?

I'm trying to solve this problem but need some help getting started. The problem asks to find all the basic feasible solutions of the following system: $$ \begin{aligned} -4x_2+x_3 &= 6\\ 2x_1-2x_2-x_4 &= 1\\ x_1, x_2, x_3, x_4 &\geq 0 \end{aligned}…
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Proof of Why Optimal Solutions Occur at Extreme Points

I'm taking my first class in Linear Programming. The book I am reading from is good in that it uses a lot of examples, but bad in that it provides few proofs. I need a proof for the following theorem. Theorem: If the constraint set $S$ of a…
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Maximize $Z=-x+2y$ given $x\geq 3,\ x+y\geq 5,\ x+2y\geq 6,\ y\geq 0$

I am a highschool senior that's new to this topic. So, apologies for my lack of knowledge and misconceptions. The proof of the theory of this chapter is beyond the scope of my textbook, so that may be reason why I feel it difficult to do the…
Nick
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What's a basic solution, and how do we find them?

I've just started learning linear programming, and for some reason, have run into a question about something that isn't mentioned in the first chapter (and we're supposed to answer these questions based on the first chapter). What is a "basic"…
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Linear Programming and Standard Form

In order to find the dual of a primal linear program, do I always have to convert it to the standard form first? For example, if I have the following LP, would the dual also be a min since the LP in standard form is a maximization?
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Finding lexicographic maximum point using a linear program

I'm trying to find the lexicographical maximum point of a bounded polyhedron, i.e. I have a set $P = \{x \in \mathbb{R}^n : Ax \leq b\}$ and I'm looking for the lexicographic maximum point of this set. Note also that every component of $x$ is…
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Runs in Rummikub simulation in AMPL

I'm taking a class in linear programming and the project involves modelling a Rummikub game. I have made the simplifying assumptions (for now) that there is no joker and only one piece of each number/colour combination. So far what I have…
Red
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Linear Programming to find the loan plan to minimize the interest payment

Assume that it is the first of July and you are running a small shop. The sales revenue and the amount of bills you have to pay for the next six months are estimated as following: In short, you will make $4000 profit at the end of the year. However…
Ling
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Writing a linear program in standard form

Usually I have been asked to write problems in standard form that have inequalities involved. However, this problem has none and I was wondering if anyone had insight on how to go about solving it. Consider this system: $$ e_{i} = b_{i} -…
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Column generation algorithm gets stuck -- subproblem returns an existing column in master

I have implemented a column generation algorithm to (try to) solve a computationally large transportation routing problem. The gist of the algorithm is the classic column generation scheme: 1) start with a feasible (but non-optimal) set of columns…
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Linear Optimization Problem with a constraint on the cost functin

Is there a known algorithm ( similar to simplex algorithm) that solves the following problem: Maximize $c^Tx$ subject to the constraints $Ax\leq b$ and $c^Tx\leq \alpha$. It would be nice if you can provide a link to an article or software…
YoelZ
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Dual of an equality constraint in MIP

In a mixed integer programming question how one may find the dual of the equality constraint? As example: $min \quad C^T X$ $s.t. \quad aX\leq b$ $\qquad eX=d$ $\qquad X\in integers$ How to find the duals of constraints $eX=d$
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Sensitivity of a solution to an LP Problem to a change in the objective function

Suppose I have a LP problem of the kind $\max f(x) = 2x_1 + c_2x_2$, subject to several restrictions. Suppose I know that the point $(a, b)$ is optimal. How much can $c_2$ change so that $(a, b)$ remains optimal? Apparently I need that the gradient…
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Largest Circle in a Polygon

My polygon is given by $P=$$\left\{x\geq 0, y\geq 0, 3x-4y\leq 2, 4x+3y\leq 12\right\}$ Now trying to find the largest circle inscribed inside these half-planes. But whenever I formulate it as an LP problem, the answers don't make sense. I'm using…
Islands
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