Jaromił Najman

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Activity overview

Latest activity by Jaromił Najman

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Weaker constraint returns worse solution

    Hi Gabriel and Lovisa, Just from looking at the Coefficient statistics of your model, it is very likely that the algorithm runs into numerical issues and can as a result provide contradicting resul...

  • Jaromił Najman commented,

    1. Community
    2. Programming
    3. Method to speed up solving many small MIPs

    Hi Ryan, I had tried Gurobi's automated parameter tool, but I think that I used it incorrectly (on single problems) so the parameters are not consistent (outside of obvious ones like turning off t...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Problem on Optimized Parameters are 0

    Hi Annie, And I just want to double-check with you that my code does reflect my mathematical equations since I'm adding many constraints, such as U_c in order to use the exp and log operations, an...

  • Jaromił Najman commented,

    1. Community
    2. Programming
    3. Method to speed up solving many small MIPs

    Currently each solve+creation takes roughly 0.004-0.005 seconds, and I am wondering if that is a kind of limit (Python API, would using the C++ API be noticeably superior here?) Which of the two ...

  • Jaromił Najman commented,

    1. Community
    2. Programming
    3. Dual Simplex Stucks when Barrier solves the model in C++

    Hi Giorgos, I have formulate the CVRPTW problem which is solved by the barrier algorithm but when the dual simplex method crossover comes to optimize the solution it stucks forever showing me logs...

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    • Jaromił Najman
    • Edited
    • 0 votes

  • Jaromił Najman commented,

    1. Community
    2. Programming
    3. Presolve is successful in removing all binary variables

    Hi Hussein, What does it mean when gurobi uses the Presolve, and now the Presolve removes all binary variables? Does that mean the problem can be formulated without binary variables?  Theoretical...

  • Jaromił Najman commented,

    1. Community
    2. Algorithms
    3. Improving Performance on 'Easy' Problems

    Hi Nate, It seems like I am taking silly run-time hits like ~0.004s to simply update the constraints. Normally, these would be negligible, but the 'easiness' of the problem means that such hits ar...

  • Jaromił Najman commented,

    1. Community
    2. Programming
    3. Restricting multiple flows in network

    Question 1: When modelling the binary constraint for flow, should I model it as this  for t in time:     m.addConstr((flow_bin.sum(i,j,t) <= 1)) or as this for t in time:   m.addConstr((flow_bin...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Problem on Optimized Parameters are 0

    Hi Annie, From the IIS you posted, you can see what is causing the infeasibility. Variable \(U_c\) is \(\geq 0\) and \(2.113 \cdot eigen_{cc} \geq 1.132740541274324 \). So in order to make the mode...

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    • Jaromił Najman
    • Edited
    • 0 votes

  • Jaromił Najman commented,

    1. Community
    2. Algorithms
    3. Increasing NumericFocus makes problem infeasible

    Hi Kazi, This particular issue has been fixed already for v9.1.2. Could you please share the model where you experience the problematic behavior? In order to generate a model file, please use the w...