## Search found 108 matches

2 years ago
Forum: Solvers
Replies: 26
Views: 11064

Fred wrote:
2 years ago
GAMS/CPLEX does not distinguish between a default 0 and an explicitly set 0.
wow Fred! I know I will regret forgetting this when I try to use mipstart. This should be in the GAMS/CPLEX mipstart docu, imho.

Thanks for this insight !!
Claudio
2 years ago
Forum: Syntax
Topic: How to model iterative calculation?
Replies: 3
Views: 1683

### Re: How to model iterative calculation?

What is iterative about the problem statement ?

or:

Why isn't b = -2 the solution ?

Best
2 years ago
Forum: Solvers
Replies: 26
Views: 11064

So, running with fixed variables finishes in "optimal solution" ? Are you initializing all variables in your problem ? Remember that, because of your GAMS version you don't have full access to mipstart options. I'm just rehashing this post by Fred, but you don't specify if it is a full solution, and...
2 years ago
Forum: Syntax
Topic: Multiplying binary variables
Replies: 7
Views: 2795

### Re: Multiplying binary variables

I get the feeling we are misunderstanding. How does a(i,t) represent a color ? Is it like

Code: Select all

t colors /red,blue,green/
a(i,t) = 1 means that point i is colored color t ?
2 years ago
Forum: Syntax
Topic: Multiplying binary variables
Replies: 7
Views: 2795

### Re: Multiplying binary variables

Point i and j will still have the same color. If points are not connected they might have the same color, only if they are connected they must have. So, the logical condition is b(i,j) = 1 ==> a(i,t) = 1 for all t b(i,j) = 1 ==> a(j,t) = 1 for all t ( Notice that this allows a(i,t) = 1 and b(i,j) =...
2 years ago
Forum: Syntax
Topic: Multiplying binary variables
Replies: 7
Views: 2795

### Re: Multiplying binary variables

While making out an example, I ran into the following:

What happens if

b(i1,i2) = 1
b(i2,i1) = 0

?
2 years ago
Forum: Syntax
Topic: Multiplying binary variables
Replies: 7
Views: 2795

### Re: Multiplying binary variables

Hi: My intuition is that your problem can be written as a MIP, but I wasn't able to understand the logic. Whenever b(i,j) =1 , a(i,t) should also be 1, but for both alias Are you saying that b(i,j) = 1 if and only if a(i,t) = 1 for all t b(i,j) = 1 if and only if a(t,j) = 1 for all t ? If you could ...
2 years ago
Forum: Modeling
Topic: solving a model with deferent solvers
Replies: 5
Views: 1999

### Re: solving a model with deferent solvers

what is wrong with yours ?, or: what is your definition of "better" ?
2 years ago
Forum: Syntax
Topic: Objective with if-condition
Replies: 28
Views: 8515

### Re: Objective with if-condition

Hi Peter, So you suggest that I should not define variables in equations but rather define them immediately? So instead of having for example No, I'm not suggesting that ! Your code is totally correct. Your problem is just your conceptual understanding. This is a little hard to explain not in person...
2 years ago
Forum: Syntax
Topic: Objective with if-condition
Replies: 28
Views: 8515

### Re: Objective with if-condition

Hi Peter: What Fred told you is very correct. Just to sum up, would you please follow his recommendation and: 1. Provide a feasible solution for the problematic situation (more than one household) and use the equation listing to tell which constraints are infeasible. The steps to do this have been d...