Unanswered Questions
862 questions with no upvoted or accepted answers
6
votes
0
answers
237
views
Provide basic solution to CLP
I'm using Pyomo to formulate an LP with approx 500,000 constraints and 200,000 decision variables. The LP is solved using CLP. Some instances fail to return even a feasible solution after many ...
- 89
6
votes
0
answers
145
views
Cases where RLT/SDP relaxation does not work well with standard quadratic optimization
(For people who don't know what RLT is): I am maximizing an indefinite quadratic function over a standard simplex, i.e., the standard quadratic optimization problem. A well-known approach is to relax ...
- 4,010
6
votes
0
answers
100
views
Proof that the leaving variable cannot be selected as the entering one in the next round
Using the Dantzig's pivoting rule, can it be proven that the leaving variable of one round cannot be selected as the entering variable in the next round?
6
votes
0
answers
87
views
How to communicate number of integer combinations to a user
I'm working on a nifty little feature for our next release, i.e., to print the number of possible integer combinations left during branch and bound.
This is really handy for the user because they ...
- 5,442
6
votes
0
answers
757
views
Solver for Go Programming Laguage
Has anyone used MIP solvers (open source or commercial) with Go language https://golang.org/? I am looking for a solver for simple linear MIPs for network flows and set cover types of problems.
- 141
6
votes
0
answers
59
views
Semi-definite Programming, non standard notation
The usual way to define a semi-definite program (SDP), e.g., as given in Boyd and Vandenberghe's convex optimization book, is:
$$
\begin{array}{cl}
\min & c^\top x \\
\mathrm{s.t.} & 0 \succeq ...
- 4,010
6
votes
0
answers
227
views
OptionalIntervalVar enforced but not working OR-TOOLS
I'm using OptionalIntervalVar and then maximizing the starts. The optimal solution is not affecting the other variables that creates the ...
- 1,895
6
votes
0
answers
187
views
Benefits of removing slack variables during presolve
I was reading Tobias Achterberg's thesis, and on page 138 he mentions the following presolving technique for linear equations (I'm slightly paraphrasing Example 10.2):
Consider the equation $4x_1+...
- 12.2k
6
votes
0
answers
144
views
Can demand be modeled by a limited amount of probability distributions?
In stochastic inventory control, it is very important to model the demand appropriate to set e.g. order levels. Demand can be fit to a certain probability distribution via many means (e.g. a goodness ...
- 1,043
6
votes
0
answers
166
views
Modelling issue with precedence constraint in OR-Tools
I'm trying to solve an RCPSPDc model It is infeasible, although Ilog Cplex solves it, so I think I have a modelling issue. I have more constraints but the precedence is the one that makes it ...
- 2,865
6
votes
0
answers
91
views
Data Formulation for Mixed-Integer-Programming Models
Until now, I have used the Gurobi, CPLEX and OR-Tools (GCO) interface to formulate mixed-integer-programming models.
Recently, I have discovered MiniZinc and want to utilize it to formulate big ...
- 2,865
6
votes
0
answers
107
views
Demonstrating a given solution is basic for a MCFP?
Given a minimum-cost flow problem, how could I go about demonstrating that a specific solution (as sets of basic and non-basic (!) arcs that build a rooted spanning tree for a given graph) is basic ...
- 253
6
votes
0
answers
651
views
Cplex is stuck after root node relaxation solution
I am solving an MIP through Benders decomposition (coded both generic and legacy callback versions), by employing Java with Cplex 12.9. For some of the instances, Cplex is stuck for two hours (time ...
- 5,442
6
votes
0
answers
173
views
Minimization of car cost during 4 years problem
I am going to buy a family car at the beginning of the New Year. I am going to stay in the UK for the next 4 years. I am considering the possibility of being a customer of company A which sells BMW ...
- 107
6
votes
0
answers
62
views
DOE Output Versus Testing Against Baseline
I am doing some output analysis on a discrete event simulation model and trying to interpret the results. My first step was to run the baseline model to get the response variable, let's say it's 10 ...
- 8,677