Jaromił Najman

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Latest activity by Jaromił Najman

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Optimal value function of the bellman equation

    The Bellman equation describes a dynamic decision problem in the optimal control theory. It cannot be directly translated into a mathematical optimization model unless you define it only for a spec...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. node time keeps increasing

    Thank you for the log snippet. You can see 2 quite serious warnings. Warning: Thread count (16) is larger than processor count (8)          Reduce the value of the Threads parameter to improve perf...

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  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. How to solve the error "model.Q not representable "

    Hi Cai, I wonder what is the maximum limit of the matrix Q, is it because my matrix Q is too big? The maximum limit of nonzeros for matrix Q is currently 2 billion (\(2\cdot 10^9\)). If you want ...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Declare objective function and constraints in Python

    Hi Agustino, This kind of function and constraints are thoroughly discussed in the posts Nested sum using quicksum() Nested quicksum function? Nested quicksum Difference between nested quicksum an...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Efficient way to avoid quadratic constraints

    Hi Fabio, Good to hear that you are making progress. Just a question: Is it more efficient or correct to use 0.5 instead of 1, considering that all variables are integers? It is not more efficien...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Modeling issue of dealing with fractions of variables and computation issues of solving the model

    You say that you allow \(y\) to attain the value \(0\), i.e., you theoretically allow for the term \(\frac{1}{0}\). If I understand your formulation correctly, if \(y=0\), then \(\mu\) can attain a...

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  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. node time keeps increasing

    But from the log i can see the barrier method already solved something ? What you see is the solution of the root node relaxation which usually only takes a fraction of the actual B&B algorithm. ...

  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Efficient way to avoid quadratic constraints

    I am not sure whether it is the most efficient way of formulating \(S_{i,k} \neq S_{j,k}\) but you could use the addGenConstrAbs method to formulate \[\begin{align*}\text{auxvar} &= | S_{i,k} - S_{...

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  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Unbounded constraint

    Hi Jun, For the \(\min\) function, you can use the addGenContrMin method. Note that you will need an additional auxiliary variable to model the \(\min\) function. Regarding the indicator constraint...

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  • Jaromił Najman commented,

    1. Community
    2. Modeling
    3. Binary Variable Involving Case Brackets

    You are trying to access \(\texttt{X[edge]}\) but you define only a single variable \(\texttt{X}\). F_ij = {} for edge in edges: F_ij[edge] = sum(flow[(k, edge)] for k in pmu_nodes)    X[edge] ...