Silke Horn

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Activity overview

Latest activity by Silke Horn

  • Silke Horn commented,

    1. Community
    2. Systems
    3. figuring out resource requirements

    There are a few things I notice from your log: First of all, the error message from the scheduler says TIMEOUT. So I guess more time would help. :-) Why does it time out? Is there a hard limit on ...

  • Silke Horn commented,

    1. Community
    2. Modeling
    3. Linear program with ceiling or floor functions (HOW?)

    You could model the expression \(\lfloor x\rfloor\) for a decision variable \(x\) by introducing a new integer variable \(y\) and adding the constraints $$y <= x$$ $$y + 1 >= x + \epsilon$$ where \...

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    • Silke Horn
    • Edited
    • 1 vote

  • Silke Horn commented,

    1. Community
    2. Modeling
    3. Mapping two sets and set alias

    Hi Buddi, Welcome to Gurobi! To define sets, you can use anything that Python offers. E.g. you could define your sets using starting_city = {"City1", "City2", "City3"} and ending_city = starting_ci...

  • Silke Horn commented,

    1. Community
    2. Algorithms
    3. add sum of square root constraint

    Hi Yutaka, Do I understand correctly that you want to add a constraint containing a term like the following? $$\sum_{i=0}^m \frac 1{\sqrt{V_i}}$$ What are the \(V_i\)? Are those decision variables?...

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  • Silke Horn commented,

    1. Community
    2. Algorithms
    3. Special knapsack problem

    The solver tries to apply all kinds of cuts when solving a model and chooses automatically how aggressively each kind of cut is applied. In the final overview, you only see the ones that were not d...

  • Silke Horn commented,

    1. Community
    2. Algorithms
    3. Unexpected behaviour of Crossover algorithm

    Hi Henrik, When using the barrier algorithm, the random seed affects mostly the ordering (and maybe the cleanup). For some models it has a bigger influence on running time than for others. I am not...

  • Silke Horn commented,

    1. Community
    2. Algorithms
    3. Unexpected behaviour of Crossover algorithm

    You're right. I hadn't paid attention to the objectives and iteration numbers before. Maybe the differences are due to chance? Have you tried running the same settings multiple times with different...

  • Silke Horn commented,

    1. Community
    2. Algorithms
    3. Unexpected behaviour of Crossover algorithm

    Hi Henrik, If you look at the logs, you can see that the barrier was a bit faster with the bigger tolerance: 424.06 seconds for 1e-7 versus 428.05 seconds for 1e-9. However, the crossover took a lo...

  • Silke Horn commented,

    1. Community
    2. Programming
    3. something wrong with my MILP model

    I am glad you could figure it out. From what I have seen, your code looks all right now. The last screenshot shows a Gurobi log, which means that the solver is running and optimizing your model. De...

  • Silke Horn commented,

    1. Community
    2. Programming
    3. something wrong with my MILP model

    You create a (and b) variables with indices from 1 to 24. In the problematic constraint, however, you are trying to access a['Delta', 25] (which does not exist). Where you create the problematic co...