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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Showing that if the Primal Program is unbounded then the dual is necessarily infeasible

On my linear programming midterm we were asked the following question. I received a 5/10 on this so I would like to know where I went wrong in my explanation. $$ \text{max } c^{T}x \\ \text{subject to } Ax \leq b \\ x \geq 0 $$ a) Write down the…
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Why do linearly independent constraints correspond to a basic solution?

Let $P$ be a polyhedron in $[0,1]^n$ defined by the constraints $Ax \leq b$ for $A \in \mathbb{R}^{m \times n}$, $x \in \mathbb{R}^n$, and $b \in \mathbb{R}^m$. In the solutions of an exercise, the following is mentioned: "Since the first $n$…
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In linear optimization, what do you call a variable whose value is derived from the value of one or more decision variable?

My view of classes of variables in linear programming is as follows: The optimization variable (which is to be maximized/minimized) Decision variables (Which I control/choose the value of in order to set the variable to be optimized to ts ideal…
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A LP model for production of two kinds of microphone

Here is a LP problem: A company produces two kinds of microphones: large and small. The expected demand for the first 3 months of the year is shown below: The first month : 400 small microphones, 200 large microphones The second month :…
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Basic solution, basic feasible solution, degeneracy

I have this matrix $$A = \begin{bmatrix}3&0&1&1&0\\2&1&0&0&0\\4&0&3&0&1\end{bmatrix}$$ and $$b = \begin{bmatrix}5&3&6\end{bmatrix}$$ So this questions asks me to find if it's a basic solution, basic feasible solution and if its a degeneracy. For…
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Analyze a combination problem : Why not producing more and Why advertising on just $1$ product?

Question : A company produces three kinds of gas ( Kind $1$, $2$ and $3$ ). Each kind of gas is made from combination of three kinds of petroleums ( Kind $1$, $2$ and $3$). The price of one barrel of the first kind of petroleum, the second…
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Linear Programming Optimal Solution at (0,0)

I'm starting to learn about linear programming. On one of my HW questions I was able to write the LP, graph (shown below), and find the optimal solution (3,2) without a problem. When I checked my solution in the manual, I had everything correct…
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General solution of linear programming is a convex combination of basic solutions?

Consider a linear programming problem of the form: $$ \max \vec c \cdot \vec x \quad \text{s.t.}$$ $$\mathbf{A} \cdot \vec x = \vec b,\quad \vec x \ge 0$$ It is known that either this problem is infeasible or it has an optimum basic solution (where…
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Linear programming problem to minimise capacity of a truck

A steel company is faced with the problem of transporting coal from two coal mines to four of its steel plants. The amount of coal available in the coal mines are $a_1, a_2$ metric tons. The amounts required at plants are $b_1, b_2, b_3, b_4$ metric…
Tosh
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How to solve this linear programming problem question?

We are started Linear programming problem question. Questions provided in examples are easy. And in exercise starting questions are easy to solve. As we have given conditions to form equations and solve them. But this question little…
user404716
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Why some solutions don't show up as corner points while optimizing functions?

I was optimizing f(x)=38000-30000x-8000y. Constraints:- 38000x+8000y<=38000 30000x+8000y>=15000 x>=0, y>=0, I Got minimum Values at two corner points (0,1.875) & (0.5,0). But when I did some grunt work I also found that (0.233333333,1) was also a…
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LP Solver performance: Tradeoff between variables and constraints

I have a problem which can be written in two ways. A simple example: More variables, less constraints: $ min\ x\\ s.t.\ x = \sum_{i} b_iy_i\\ m_1 \leq x \leq M_1\\ m_2 \leq y_i \leq M_2 $ Less variables, more constraints: $ min\ \sum_{i}…
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When does $\max x+y $ subject to $ax+by \le 1$, $x,y\ge 0$ have a unique optimal solution?

From reading online I found someone said that it has a unique optimal solution when $a$ and $b$ are positive and $a \neq b$. Could someone explain why this is the case? I know that if $a = b$ then any x,y values that satisfy the equation $x + y =…
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linear programming problem pivot selection

I am using pythons linprog to solve the following linear program. I am using a callback to have linprog display the tableau on each iteration below. I don't understand how the last tableau is calculated. I would think the pivot would be 1 (row…
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Solving a linear programming problem with different constraints

A project involves three activities $a_1, a_2$ and $a_3$. $a_3$ can start only after $a_1, a_2$ are completed. The amount of work done by a single worker in a day for the activities are 2, 3 and 1 units respectively. The total amount of work for…