Questions tagged [duality]

For questions on duals of (primal) mathematical programs that optimize the complementary bound. When minimizing, for example, primal solutions are upper bounds, and dual solutions lower bounds on the optimal value.

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12
votes
2answers
125 views

Dual bounds of integer programming problems

I often read in papers when branch-and-X algorithms are used to solve mixed integer programming problems, that the lower bound (in the minimization case) obtained from solving a linear programming ...
12
votes
0answers
100 views

Integrality gap in bilevel binary linear programming problem

I have a bilevel max-min optimization problem over binary variables, with constraints expressed using linear inequalities. The inner (minimization) problem is $$ \begin{alignat}2 \min\limits_x&\...
8
votes
1answer
144 views

Is there any relationship between KKT and duality?

I noticed the similarities between KKT and complementary slackness, but I do not fully understand it.
9
votes
1answer
124 views

Finding Dual Objective

I have the following simplified optimization problem: \begin{align}\max &\quad ax+by\\\text{s.t.}&\quad0 \le x \le \overline X\\&\quad0 \le y \le\overline Y\\&\quad z = E-x+\beta\cdot ...
14
votes
1answer
351 views

Duality in mixed integer linear programs

I know that the standard duality theory for the linear programming problem does not hold for mixed integer linear programming problems. I was wondering why an integer program does not have a dual ...
13
votes
1answer
128 views

Robust counterpart: why is dual reformulation not working?

I am trying to solve robust optimisation problems, but I am getting nonsensical solutions most of the time… Here is a very simplified example: \begin{alignat}{2}\max&\quad x+z&\\\text{s.t.}&...
17
votes
2answers
278 views

Tool to get dual problem from any linear optimization problem (.lp)

Is there a tool that reads any linear optimization problem (for example an .lp or .mps file), converts it to the dual problem and prints the dual problem?
11
votes
1answer
126 views

How to relate dual values of valid inequality to the dual values of the original problem?

I have a given formulation that looks like this (just for the constraints): $$\sum_i \beta_{i,j} \geq \alpha_j,\qquad\forall j$$ $$\alpha_j \geq \sum_i f_{i,j},\qquad\forall j$$ $$\alpha_j \geq 0, ...
11
votes
1answer
168 views

Recovering primal optimal solutions from dual sub gradient ascent using ergodic primal sequences

My question concerns recovering a primal optimal solution while performing dual sub gradient ascent. Denoting by $y_i$ the dual multiplier in the $i^{\text{th}}$ iteration, let \begin{equation} x_i = ...
12
votes
2answers
372 views

Correct way to get a dual extreme ray for an infeasible LP in CPLEX / C++

We are coding a Benders decomposition using CPLEX/Concert (C++) and we are having some troubles to generate a feasibility cut because we are not sure how to get an extreme ray of the dual for a primal ...
16
votes
3answers
140 views

How to take the dual of a conic optimization problem?

Given a conic problem $$\min \{c^\top x \mid Ax \succeq_\mathit{C} b\}$$ for an arbitrary cone $C$, how can I construct the dual to the problem? Moreover, in Linear Programming one constructs the ...
19
votes
4answers
230 views

How can I remember the rules for taking the dual of a linear program (LP)?

When taking the dual of a linear program (LP), is there a trick/easy way to remember the rules for the directions of the inequalities, signs of the variables, etc.? A trick with a catchy name, perhaps?...