Search found 113 matches

by dirkse
9 months ago
Forum: Archive Google Group
Topic: Is it possible to solve bi-objective model directly in GAMS?
Replies: 6
Views: 1203

Re: Is it possible to solve bi-objective model directly in GAMS?

Richard, Your last post gave lots of specifics related to the algebra of your model, but my question was more basic: what does it mean to say that a point is a solution? For example, a point xbar solves a uni-objective model min z = f(x) if xbar is feasible and f(xbar) <= f(x) for all feasible x. -S...
by dirkse
9 months ago
Forum: Archive Google Group
Topic: Is it possible to solve bi-objective model directly in GAMS?
Replies: 6
Views: 1203

Re: Is it possible to solve bi-objective model directly in GAMS?

Richard, Your post raises an interesting question. What exactly is a bi-objective model? The name seems self-explanatory and self-contradictory at the same time (e.g. "We need to both minimize costs and maximize production.") To be complete a definition would include some characterization of what it...
by dirkse
9 months ago
Forum: Modeling
Topic: Problem with the same code between different computer
Replies: 2
Views: 421

Re: Problem with the same code between different computer

Hello, You define a model and solve it, with a time limit of 15 seconds. It is not surprising that different computers make different amounts of progress before they hit the time limit and return the incumbent solution. In fact, you should expect to see this same behavior even on the same computer. ...
by dirkse
10 months ago
Forum: Solvers
Topic: Help me in CES, CET estimate, please
Replies: 12
Views: 1345

Re: Help me in CES, CET estimate, please

Hello, CONOPT has hit the iteration limit you set, so it stopped. Always look at the SOLVER STATUS and the MODEL STATUS before looking at the variable values. You could also use some GAMS code to print a message or abort if the solver didn't find a solution. This is sometimes better than continuing ...
by dirkse
10 months ago
Forum: Syntax
Topic: Record optimality gap at different CPU times
Replies: 1
Views: 411

Re: Record optimality gap at different CPU times

Amirhossein, The solvers XPRESS, SBB, and CPLEX all have a mipTrace facility that records bestBound/bestFound values. You can create what you want from this. https://www.gams.com/latest/docs/S_XPRESS.html?search=miptrace https://www.gams.com/latest/docs/S_SBB.html?search=miptrace https://www.gams.co...
by dirkse
10 months ago
Forum: Archive Google Group
Topic: Dijkstra's algorithm
Replies: 9
Views: 2511

Re: Dijkstra's algorithm

rawwi,

No, you cannot easy modify Dijkstra's algorithm to force the shortest path to go through all nodes. This would essentially give you a solution to a traveling salesman problem on the same network, which is a much more difficult problem.

-Dirkse
by dirkse
10 months ago
Forum: Modeling
Topic: Writing model tests - best practices
Replies: 4
Views: 689

Re: Writing model tests - best practices

Chris, You wrote about the remaining tedium: But even though the task is automated, it is still tedious: On the one hand, the "local" model check takes quiet long (ca. 30min, as every scenario has to be solved), and I don't see any way in reducing the required time significantly. Furthermore, there ...
by dirkse
10 months ago
Forum: Syntax
Topic: ERRSAMBAL/SAMBALCHK
Replies: 1
Views: 360

Re: ERRSAMBAL/SAMBALCHK

Judith, If the numbers balance somewhere else and they don't in GAMS, I would start by checking if I am really using the same numbers in both places. I would also look at the larger entries in the sambalchk parameter. If you dump that to GDX immediately before the division you can browse it afterwar...
by dirkse
10 months ago
Forum: Modeling
Topic: Conditional Binary
Replies: 1
Views: 328

Re: Conditional Binary

Omi, To paraphrase your question, you ask "How can I have a condition iff a binary variable is 1", e.g. for a binary y expression >= 1 implies y = 1 expression < 1 implies y = 0 This doesn't work well. Strict inequalities are not part of optimization for several reasons, e.g.: http://yetanothermathp...
by dirkse
10 months ago
Forum: Modeling
Topic: maximum and minimum value
Replies: 3
Views: 408

Re: maximum and minimum value

Steffen, In your model you will always have non-unique solutions. For any solution, you can just add some arbitrary positive amount to both Market_Purchase_Quantity and Market_Sell_Quantity and you'll also get a solution. What is perhaps unique about the solution is the difference between these two:...