Unanswered Questions
121 questions with no upvoted or accepted answers
7
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What distuingishes a model-and-run framework solver from a programmatic solver?
I am looking for examples to understand what kind of benefits a model-and-run framework solver offers that a more programmatic solver doesn't do or doesn't do as well.
What distinguishes a model-and-...
7
votes
0
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885
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Having trouble with objective function in Python: "GurobiError: Variable not in model". What else could I try?
I am trying to figure out how I can write this objective function into python using Gurobi. I have to minimize the sum of the product of three dictionary's values. The reason I am confused is that ...
6
votes
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651
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Cplex is stuck after root node relaxation solution
I am solving an MIP through Benders decomposition (coded both generic and legacy callback versions), by employing Java with Cplex 12.9. For some of the instances, Cplex is stuck for two hours (time ...
6
votes
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447
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How to make constraints satisfy disciplined convex programming guidelines?
How do I turn my convex constraints (described below) into constraints that are DCP so that I can solve them in CVXPy? Is there some ``cheat sheet'' of standard tricks?
I'm trying to implement the ...
5
votes
0
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238
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How to use interpolation for problem parameters in Pyomo
I'm working on my first Pyomo DAE project to teach myself how to use it for trajectory optimization. I have generated an atmosphere lookup table with density and speed of sound as a function of ...
5
votes
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124
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Scale of largest CPLEX/Gurobi execution
I am trying to understand the CO2 emission of large scale optimization using CPLEX or Gurobi. Is there a published literature which addresses the compute usage of large scale executions?
5
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121
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Reduce overhead Gurobi Python getting and setting attributes
I am using Gurobi 9.5.1 in Python 3.10. In the context of column generation I request the duals of the master problem and set them in the objective of the subproblem. This is done repeated times.
<...
5
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153
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How to handle constraints in docplex to states the relation between two variables?
I am using docplex.cp and I need to state the following constraint:
$$\sum_{c}(X_p{_w}_{cj}+X_{p+1}{_{w'}}_{cj+1})\leqslant T_w{_{w'}}_{,jj+1} + 1$$
Knowing that the binary variables are:
$X_p{_w}_{...
4
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159
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4
votes
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385
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CPLEX Python: Current subproblem model in branch and bound
I have an MILP problem and use CPLEX (Python interface). I am working on user heuristics for branching in the branch-and-bound procedure. With HSCallback I managed to get the information about the ...
4
votes
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272
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Does anyone have the criss cross algorithm programming code to solve linear programming problems?
I have a project that requires programming code for the simplex algorithm and criss-cross algorithm. The purpose of this project is to compare the two methods. I've tried to find it, but the ...
4
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87
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Problem related to machine's performance while solving an LP-relaxation of a set-covering problem using the Column Generation
PS: I am familiar with performance variability encountered while solving large-scale MIPs. My question may not be explicitly related to it but maybe to the inefficiency of python packages.
I have ...
3
votes
1
answer
210
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Implementing Logic-based Benders decomposition on a single search tree
Currently, I am working on a scheduling problem and trying to approach it by the logic-based Benders decomposition method. Theoretically, I have everything, i.e., the master and sub problem(s), the ...
3
votes
0
answers
100
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Pygmo2: What is the point of evolving an archipelago in a loop if number of generations already set in algo
I want to solve a multi-objective problem with nsga2 or moead taking advantage of the parallelism available in pygmo library. I have seen a very nice example on github posted below. However I am not ...
3
votes
0
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87
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Minimize total cost to buy unique products over timespan
I am looking for some guidance on how to better state my problem formally and practically (e.g., relevant Python libraries).
Let's assume I have a set of $X$ unique products to buy. I have $Y$ days in ...