Tobias Völk
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Latest activity by Tobias Völk
Tobias Völk created a post,
Bug? Numerical Issue? Help! Optimal objective value of relaxation is negative despite being the sum of nonnegative variables?
Awaiting user inputSo I was using slack variables (indicating how much a constraint is violated for > 0, = 0 means that the constraint is fulfilled) to find any feasible solution as fast as possible (why doesn't Guro...

Tobias Völk commented,
The alternative form is what I was looking for, thanks :)

Tobias Völk created a post,
Change objective function during optimization
AnsweredWe cannot use a certain type of cut with Gurobi because it requires the replacement of a part of the objective function in the callback. It would be cool if there was some "onyourownrisk"way of...

Tobias Völk created a post,
Query ruled out values for binary variables in callback
AnsweredWhen Gurobi knows, that there is no feasible/optimal solution with (binary variable x_3) x_3 = 1, it would be cool if this could be queried during the callback. Not that Gurobi should try to look f...

Tobias Völk created a post,
Proper way to access LP relaxation?
AnsweredWhen Gurobi has solved a relaxation during it's Branch & Bound  Algorithm, I would like to look at the solution of the relaxation in order to add a type of cut which we found in a paper. What is t...

Tobias Völk created a post,
Query which binary variables have known values during optimization in order to add additional constraints
AnsweredIf it doesn't exist yet, it would be a cool feature to have. Having binary variables x_1, x_2, ... Gurobi does rule out values for variables during optimization, right? For example, if it has deci...

Tobias Völk created a post,
Indicator constraints with arbitrary righthandside (Python)
Answeredmodel.addGenConstrIndicator(...) As far as I can see (though that does not mean much of course), there is no reason why the righthandside has to be a float. Neither Math nor Python should pose a ...

Tobias Völk created a post,
Optimizing away dummy binary variables with values determined by other variables?
AnsweredHi all, we have the following part of our problem formulation: x_t = 1 IFF machine is on at time t ELSE 0 u_t = 1 IFF machine was started (u)p, meaning x_(t1) = 0 AND x_t = 1 ELSE 0 d_t = 1 IFF ma...

Tobias Völk created a post,
Model too big for academic license
AnsweredMe, a curious student, was so so excited to finally have modeled their first optimization problem using Gurobi and thus having found a much faster way to solve their problem for big sizes, soon had...