Jaromił Najman

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Activity overview

Latest activity by Jaromił Najman

  • 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
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  • 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 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...

  • Jaromił Najman commented,

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

    In this part, the I want to constrain the flow from inland terminals. Such that only one of them should be able to provide containers. If I were to do it for every i j in nodes then port will be i...

  • Jaromił Najman commented,

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

    However, will I have to do it individually if the problem has many more variables? You somehow have to provide this information to Gurobi. If you have the optimal solution point as some data stru...

  • Jaromił Najman commented,

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

    Hi Annie, Posting screenshots of your code makes it very hard to provide help because one cannot copy and paste your code. If you would like to share big chunks of code, it is best to upload the fi...