 # Jaromił Najman Gurobi Staff
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## Activity overview

Latest activity by Jaromił Najman
• Jaromił Najman commented,

If you look at the two constraints $$\texttt{R93}$$ and $$\texttt{R98}$$, you will see that both constraints have the exact same left-hand side and set the respective left-hand side to either 1 or ...

• Jaromił Najman commented,

Hi Iria, This sounds interesting and I would like to investigate further. Could you please share the graph coloring models and the symmetry breaking constraints that are necessary for this performa...

• Jaromił Najman commented,

The Knowledge Base article How do I determine why my model is infeasible? explains how to proceed in such a case.

• Jaromił Najman commented,

In your code $$\texttt{Expo_noise_matrix}$$ is a range object and thus, you cannot assign values to it. You should rather use a dictionary for $$\texttt{Expo_noise_matrix}$$. Time_span = 16Expo_noi...

• Jaromił Najman commented,

If I change the diagonal values, where the transportation takes place between $x$ to $x$ to some smaller values like 10e+6, does it work? You would have to test it yourself. It would definitely i...

• Jaromił Najman commented,

Do you have any idea of what could be my issue according to the output? You can implement any combination of $$y_{18,18} \in \{0,1\}, y_{18,40} \in \{0,1\}$$ to verify that any is infeasible. Hav...

• Jaromił Najman commented,

Hi Jacob, So, to get that straight: the long crossover time has nothing to do with the fact that I am passing a MIP model to Gurobi that is in fact LP, but because the LP (root) model is difficult...

• Jaromił Najman commented,

Hi Jacob, Usually, Crossover only takes an extraordinary amount of time if the problem is very large or if it has numerical issues. Do your models have any numeric issues? See Guidelines for Numeri...

• Jaromił Najman commented,

Did you consider skipping those entries? I assume that the fraction $$\frac{1}{|x-y|}$$ is some weight/cost coefficient for the distance from $$x$$ to $$y$$ correct? I think it is best to forbid di...

• Jaromił Najman commented,

Hi Hongyu, We are guessing Gurobi is doing analytic centre, but could anyone confirm what we thought? The Barrier algorithm without crossover, i.e., Crossover set to 0, in general returns a solut...