Search found 34 matches

by abb.omidi
3 days ago
Forum: Modeling
Topic: Lagrangian relaxation issue
Replies: 1
Views: 103

Re: Lagrangian relaxation issue

Dear community team,

If you need more details about the question I can elaborate more on this. Actually, I do not expect an exact answer and any useful insight would be appreciated.

Best regards
Abbas
by abb.omidi
1 week ago
Forum: Modeling
Topic: Lagrangian relaxation issue
Replies: 1
Views: 103

Lagrangian relaxation issue

LR_(GAP-2)_1.gms Dear community team, I am trying to solve a scheduling problem by using the Lagrangian relaxation method. As I am pretty new in this field have tried to start with a generalized assignment problem to understand how this method can work on the MILP's. Also, I have read https://my.ec...
by abb.omidi
2 months ago
Forum: Modeling
Topic: Issue about fix and dive heuristic
Replies: 0
Views: 959

Issue about fix and dive heuristic

Hi, I am trying to solve a scheduling problem (MILP) by using GAMS/Cplex. As the problem is not being solved in a reasonable time for the large-scale instance, I would like to use a simple heuristic namely fix and dive to achieve a feasible solution. What I have tried to do is, solving the original ...
by abb.omidi
6 months ago
Forum: Modeling
Topic: Issue on executing an option file
Replies: 0
Views: 969

Issue on executing an option file

Dear community team, I am trying to solve an NLP problem by using Baron solver via the Neos interface in the GAMS v.34. The option file contains two local parameters of the Baron solver and is as follows: option nlp= Baron; $onecho > baron.opt numloc 0 dolocal 0 $offecho model.optfile=1; When I have...
by abb.omidi
8 months ago
Forum: Modeling
Topic: Defining the planning horizon in the RCPSP
Replies: 0
Views: 1088

Defining the planning horizon in the RCPSP

Dear support team, I am trying to write an optimization model related to the resource-constrained project schedule based on Pritsker et al. formulation. The model is as follows: test.jpg When I have defined the objective function as shown in the model, the final solution is incorrect but, when I wri...
by abb.omidi
9 months ago
Forum: Modeling
Topic: Issue with the reformulating MINLP
Replies: 0
Views: 1019

Issue with the reformulating MINLP

Dear support team, I have tried to solve an optimization problem (an MINLP) to minimize the number of items that need to be stored. The objective function is as follows: objective function: Minimize z = sum(i, R(i)/x(i)) Where, R(i), i in {1, ..., n}, given constant and x(i) are integer variables. I...
by abb.omidi
1 year ago
Forum: Modeling
Topic: Solving MIP using MCP
Replies: 0
Views: 1054

Solving MIP using MCP

Dear community team, I'm trying to solve a BIP using MCP solver. When I run the problem I have the following issue: Discrete variables can only appear in MIP, RMIP, MINLP, RMINLP, MIQCP or RMIQCP MPEC RMPEC problems. I was wondering if, A) Is it possible to use MCP solver for BIP/MIP? B) I'm trying ...
by abb.omidi
1 year ago
Forum: Modeling
Topic: Implementing decomposition method
Replies: 2
Views: 1083

Re: Implementing decomposition method

Dear Dr Bussieck,

Many thanks for your suggestion.
As I'm not any experience in the graph colouring and I am interested in scheduling model, I'm wondering if, are there any related materials for the scheduling problems?

Regards
Omidi
by abb.omidi
1 year ago
Forum: Modeling
Topic: Implementing decomposition method
Replies: 2
Views: 1083

Implementing decomposition method

Dear support team, I have often used GAMS and now have tried to implement a Dantzig-Wolfe Decomposition for an LP problem. It works fine for a small instance. Now, I'm trying to extend the DW-based algorithm to solve the MIP model. I'm aware that some of the algorithms like heuristic-based CG, can b...
by abb.omidi
1 year ago
Forum: Modeling
Topic: GAMS Kestrel Issue
Replies: 3
Views: 2194

Re: GAMS Kestrel Issue

Dear Dr Bussieck, Many thanks for your detailed explanations. The issue was fixed and the model was solved by the kestrel. I have another issue and I was wondering if, you could advise me about that. I have tried to solve a scheduling problem and regard to, the model is a large scale, I would like t...