Search found 75 matches

by dirkse
1 week ago
Forum: Modeling
Topic: Stochastic Programming: Assign probability to multiple vector scenarios using EMP
Replies: 2
Views: 89

Re: Stochastic Programming: Assign probability to multiple vector scenarios using EMP

Rishabh, Instead of thinking of the EMP info file as independent of your GAMS model - and using data from an external source in this file - you should think of this file as an extension of your GAMS model. If you use the put facility you can easily take data that is in your GAMS model and send it to...
by dirkse
2 weeks ago
Forum: Archive Google Group
Topic: Is it possible to solve bi-objective model directly in GAMS?
Replies: 6
Views: 220

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

Richard, If we exclude the EMP model type from the discussion (that's a whole other story), then GAMS does not have a multi-objective model type. The model you describe seems to be a good representative example. You have two objectives - distance traveled and construction costs - and you'd like a so...
by dirkse
2 weeks ago
Forum: Archive Google Group
Topic: Is it possible to solve bi-objective model directly in GAMS?
Replies: 6
Views: 220

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
2 weeks ago
Forum: Archive Google Group
Topic: Is it possible to solve bi-objective model directly in GAMS?
Replies: 6
Views: 220

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
3 weeks ago
Forum: Modeling
Topic: Problem with the same code between different computer
Replies: 2
Views: 155

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
1 month ago
Forum: Solvers
Topic: Help me in CES, CET estimate, please
Replies: 12
Views: 367

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
1 month ago
Forum: Syntax
Topic: Record optimality gap at different CPU times
Replies: 1
Views: 160

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
1 month ago
Forum: Archive Google Group
Topic: Dijkstra's algorithm
Replies: 9
Views: 1537

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
1 month ago
Forum: Modeling
Topic: Writing model tests - best practices
Replies: 4
Views: 303

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
1 month ago
Forum: Syntax
Topic: ERRSAMBAL/SAMBALCHK
Replies: 1
Views: 130

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...