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Failing to meet a constraint in a NLP problem

I have a NLP problem at hand, which I am trying to solve via Pyomo + ipopt. I try to run several different instances of the optimizer with different conditions, out of which I notice that I am able to optimize for ~90% of times. In the other 10%…
chupa_kabra
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Add robustness of AMPL code through file name

I want to add robustness to my AMPL code, here is what I am actually doing: In my script I use a .txt file that contains all my parameters, let's call it "instance.txt". I want to print my result in another txt file and call it…
odd
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2 answers

Overwrite on a txt file from AMPL

I have a result I want to save in a .txt file. So I use this line to save a result k: param OutputFile symbolic := "output.txt"; print k >> (OutputFile); However, I may run the script several times which means I will open an existing file and add…
odd
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5
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CBC stalling after approximately 10 seconds

I'm using CBC with PuLP to solve a small unit commitment problem. I'm finding that with certain combinations of input parameters, CBC simply stalls. With other input parameters, it solves, usually in 10 seconds or so. I've applied a 20 second time…
Daniel
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What are examples of integral polytopes, where there exists an algorithm to write a given point as a convex combination of integral points?

Given a set of integer points $S$, one is often interested in finding $\operatorname{conv}(S)$ or characterizing certain cases, where $\operatorname{conv}(S)$ is described by few inequalities. Examples would be stable set polytope on perfect graphs…
user3680510
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Polyhedra to Simplex by using convex combination of vertices

Optimization problems over linear constraints (defining a convex polyhedron) can be written as optimization over a simplex in a higher dimension. Let $\mathcal{P}$ be a bounded polyhedron, and the vertices of this polyhedron are saved as columns of…
independentvariable
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Combined arc capacity constraints in network flows

Consider the network flow polyhedron for a directed graph $G = (N, A)$. Along with the standard flow-balance and single-arc capacity constraints, we are faced with additional constraints which enforce capacities on the total flow through subsets of…
dxb
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When is there at least an integral point in a polyhedron?

This problem comes from a problem of economics. Let $x\in [0,1]^n$. $\{x_1,x_2,\ldots,x_n\}$ is partitioned into ${S_1, S_2,\ldots,S_k}$ such that $\sum_{x_i\in S_j}x_i\leq 1$ for each $1\leq j\leq k$. This constraint can be restated as $Bx\leq 1$…
Surpass2019
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How to represent time windows as a constraint in a vehicle routing problem?

I am trying to solve a vehicle routing problem using Tabu search. I have successfully completed implementing the constraints for CVRP by giving penalties to in the objective function. How do I implement time windows as a constraint?
21vs
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Procurement and supply management: model-oriented undergradute textbook

I look for an undergraduate-level textbook on procurement and supply management that is largely organized around (reasonably simple) mathematical models. The texts I have reviewed so far are all description/discussion-based, with minimal to no…
tvk
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Quantifying Feasibility

I have a scheduling model formulation ( experimental setup) that takes in product states as input (sample points) and checks the model status (response) and returns feasible or infeasible. My plan is to be able to represent the feasible space of the…
Dare Badejo
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How to use solvers with virtual machines?

Is there any way to install and use commercial solvers (for which I have a license) on some virtual machines? For example, if it's possible to install the Octeract engine student version on a google engine virtual machine? Or use Gurobi on a VM? A…
Oguz Toragay
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Does pyomo support column generation?

I want to use column generation technique to solve cutting stock problem. Is there any other python modeling library that supports column generation?
Sina Haji Kazemi
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1 answer

how to apply Big M to model the logic constraint （if-then-else）

I was hoping to get some help in modelling the following logic as an MIP Constraint c_{m,l}^{RC} is binary decision variable. Simplify it：
xuezheng
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3 answers

Global Optimization when the exponential function is involved

I wonder if there are methods to determine the global optimum of MINLP problems, when the nonlinear functions involved are only of the form $Z = Y e^{- \alpha X}$, where $Y \ge 0$ and $X \ge 0$. Are there any papers describing such an approach? Do…
Clement
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