Questions tagged [network-flow]
For questions related to the formulation or solution methodologies of network flow problems. Some of the well-known network flow problems are maximum flow problem, minimum-cost flow problem, and multi-commodity flow problem.
86
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Shortest path problem with time as a random variable with correlation
I'm trying to solve the $\alpha$-reliable shortest path problem with correlated time variables (travel time per arc), i.e. the shortest path subject to the constraint that the probability of arriving ...
0
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1
answer
71
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Interpret the formulation of a pricing model in crowdshipping
I am trying to run the pricing model from the paper "Designing pricing and compensation schemes by integrating matching and routing models for crowd-shipping systems" on python with Gurobi, ...
2
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2
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120
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Transportation Problem
I want to create a transportation model. I have identified importing and exporting countries with their estimated demand and supply. The cost of transportation per one uni is already calculated for ...
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0
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49
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What the dual constraints mean?
I have a primal problem that is a network-flow:
$$
min_x \sum_{a \in A} c_a x_a \\
\text{s.t.} \sum_{a \in A:n = v} X_{a}-\sum_{a \in A:n' = v} X_{a} = \begin{cases} \;\;\;1, \; v=n^{in} \\ -1, \; v=n^...
- 507
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28
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When Supply < Demand - distributing resources v/s meeting as much demand
In network modelling LP , when Supply < Demand and we use normal balance of flow rule for all the constraints, i.e. (inflow - outflow) <= supply or demand, we say we are trying to redistribute ...
3
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0
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66
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Flow problem with flow demands
Recently I found a subproblem in a project I am working with. This problem is a sort of flow variant, as you will see. And I am looking for literature-related articles and also fast approaches for ...
- 1,091
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2
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236
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Graph models - Maximum flow problem and minimum cost flow problem
I'm trying to solve this problem:
An investment agency holds the rights to six investment projects: I1, I2, ..., I6. Projects I1, I2 and I3 are research and
technological development projects and the ...
- 119
4
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0
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646
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Google-OR tools vs Pyomo and other commercial Solvers for solving a simple maximum flow problem
I have implemented a Pyomo model for solving maximum flow problem as a subroutine of an algorithm. However, the approach does not scale very well because Pyomo does not provide a very good way to re-...
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2
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2
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229
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Improve Network Flow computation with additional Pyomo constraints based on previous computation
I am performing several max-flow computations on extremely similar networks and I seek to improve their execution time based on information from previous computations (As there is a lot of repetitive ...
- 392
3
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2
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114
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Partial Lagrangian in the Max-Flow problem
In the question:
"Partial" Lagrangian Dual in LP
It is argued that considering a partial Lagrangian $L_{partial}$, where we Dualize only some of the constraints, results in a tighter ...
- 143
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2
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104
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Transportation problem with consolidation within path
There's a supply network design problem that I'm trying to solve, which is as follows:
A certain amount of goods need to be transported from point A to B, and can have stoppages in between with a ...
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2
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1
answer
96
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Modify the network model to accommodate multiple vehicles
Given a directed network (or graph) $G = (V,E)$ with each edge $e_{ij}$ having a non-negative cost as the travel time from $i$ to $j$. Each node has an associated demand $d_i$. If the demand is ...
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2
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1
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60
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Find the shortest path connecting some (s,t) - a greedy (?) criterion to a multi-commodity flow problem
At page 7 from these slides there is a Greedy algorithm I want to implement.
It says
let $P_i$ be the shortest path (if one exists) that [...]
connects some ($s_j$, $t_j$) pair that is not yet ...
- 561
5
votes
1
answer
172
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Flow problem with side constraints: how to eliminate subtours?
I am working on a flow problem with side constraints. More specifically, I have a usual flow problem, with constraints that require some arcs to have exactly one unit of flow on them. This makes the ...
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0
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77
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Assignment problem with continuous constraints
I am trying to solve an assignment problem where all the variables are continuous. I have a set of sources S, and another set of destinations D. Each source and destination have capacity/demand ...
3
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1
answer
119
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Modeling a special case of conservation of flow
At a particular mode, there are 2 inflow arcs, a and b, and two or more outflow arcs, which is kept to 3 for this example, i.e., c, d and e
The first requirement is that only one of the two inflow ...
- 707
3
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1
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296
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Minimum cost flow problem with multiple arcs between nodes in Python / Google OR
Is it possible to work with multiple arcs between 2 nodes within Google OR?
Or are there better modeling techniques?
I want to optimize flow from supply to demand areas, where supply and demand are ...
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3
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1
answer
80
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Reformulating undirected to directed edges for MCF
As stated in this paper, there is a technique to reformulate a multi-commodity flow problem (MCF) with undirected edges to its equivalent version with directed edges.
By quoting them:
The ...
- 561
6
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1
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370
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How to Model Path Being Only Through Adjacent Cells
I am trying to develop a MILP for a path planning problem. I am operating on a grid of cells that represents a map. The arrangement of cells in the grid represents the placement of the cells in real ...
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-1
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1
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85
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Assignment Problem with continuous decision variable
I have to solve a problem from industry where there are a number of machines which should be assigned to a number of tasks. The difference from the general assignment problem is tough, that the ...
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1
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1
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143
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Help with dual of a problem
Could anyone confirm me if I write the correct dual for my problem? The different sets confuse me a lot.
$s$ is the source node and $t$ the sink node.
I'm uncertain if the last dual constraint in ...
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2
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1
answer
573
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Model the TSP as a shortest path
We have a directed graph $G=(N,A)$ where $N$ are the verticies $N=0,1,2,3,4,5,..,n$ the starting location is node 0.
For each arc $a=i-j$ in A we have a distance $d_a>0$
So we want to start and ...
0
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1
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107
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How to model a simple routing problem using nodes and arcs
I have the following problem.
I have a route which begins at node $0$.
I want to begin and end in $0$ which is a depot.
Now in this route even customer will be visited in order for example customer 2 ...
1
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0
answers
143
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How to see fix constraint violations found with IIS
I'm running a simple MCNF model to see if my network is balanced. I'm using Gurboi in Python and with the IIS I can see that there are 2 constraint violations making it infeasible. How do I fix these ...
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4
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492
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How to see constraint violation for network flow problem
I am testing to see if my network is balanced as part of a larger protection-interdiction-restoration problem. To do this, I'm solving the problem as a minimum cost network flow problem to see if the ...
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4
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2
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168
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How to fix unbalanced multi-commodity network flow with equal supply and demand?
I have a fairly large network with eleven commodities and arc capacities that are commodity-dependent (i.e. an arc may have a higher capacity for one commodity than another). I'm solving a protection-...
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0
answers
502
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How to eliminate large matrix coefficients and large RHS warning in Gurobi
I'm solving a large network flow problem using Gurobi to do Benders decomposition in Python. The imported .csvs contain values that typically fall in either zero, the range of [20,200], or with a ...
- 109
3
votes
2
answers
465
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Designing a multi-commodity network flow optimizer
I'm trying to solve multi commodity multi source network flow optimization problem using Python-PuLP. Here is how my problem looks like:
The numbers on the arcs represent the order of priority a ...
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2
votes
2
answers
212
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Min cut network for patients
I'm trying to formulate a min cut algorithm
There are two classes of patients: 1, 2, and the maximum number of patients that can be assigned to each bed per day is shown below as well.
$$
\begin{array}...
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6
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2
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293
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Multi-commodity Network Flow: Convert a node-arc solution to an arc-path solution
For a logistics optimization problem I am working on, the most natural expression of the problem is using a node-arc formulation of the MCNF. It is solved using an LP/MIP solver like CPLEX/Gurobi.
...
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3
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0
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132
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Sources of Min-Cost Flow Models That Utilize Binary Variables for Transportation Networks
I am looking for articles that include min-cost flow models with binary variables for flow transportation like gas networks, traffic systems, heating systems. Is there any specific place(like OR ...
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99
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Availability of library for solving generalized network flow problems
I need to solve a large-scale generalized network flow problem.
For reference, it is a pure network-flow model with the exception that arcs have a positive coefficient applied to flow on them. In my ...
2
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1
answer
303
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How to solve a minimum cost flow problem with time constraints
In the following picture, the decision-maker has to make deliveries to node $V=\{1,2,3,4,5,6\}$. He has two options: use cars or bikes. In both cases, he has to make a stop at a relay point where the ...
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0
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22
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Asserting solution existence via approximation of multi-commodity integral flow
Consider a polynomial $\epsilon$-approximation for MCF with integral flow (like the one based on LP relaxation).
Can I (in general) use this algorithm as a predicate, asserting whether a solution ...
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1
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89
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Does multi-commodity flow problem (MCF) block cycling flows?
I am working with multi-commodity flow at integral flow with unit demand for each operation.
Since I use the MCF formulation to model path finding, in my scenario cycles are just a waste of resources. ...
- 561
5
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1
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152
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(Integral) multi-commodity flow on undirected graph
Usually in (integral) multi-commodity flow problems the graph is assumed to be directed. Instead, I am working with an undirected graph. Is it possible to transform it in a digraph?
Does such a ...
- 561
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0
answers
55
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Multi-commodity flow problem reduction
Assume to tackle a particular group of instances for the integral multi-commodity flow problem.
Particularly, given a digraph $G = (V \cup S \cup T,E)$, such that $S, T, V$ are all disjoint. ...
- 561
1
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0
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44
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Solving a max-flow problem through lex-max flow problem
Assume that, for a given network, its multi-sink multi-source max-flow satisfies a lexicographic order. Is this enough to state that I can solve the max-flow problem, by using a lex-max solver (i.e. a ...
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Complexity of lexicographic integral flow
I read that the lexicographic flow problem is polynomially solvable. However it allows for continuous flow values.
Is there any reference about the problem with integral flow (and its complexity)?
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Is there a difference between "Integral Quickest Transshipment" and "Integral Quickest Multicommodity flow"?
I can't get the difference between this two problems, which seem equal to me.
But, for the former, a polynomial solver is known, while, for the latter, it is not.
EDIT - References:
...
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3
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1
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423
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Is Multicommodity Flow problem really NP-hard?
Within paper ON THE COMPLEXITY OF TIMETABLE AND MULTI-COMMODITY FLOW PROBLEMS
there's a proof that the multi-commodity is NP-hard.
While in ...
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2
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395
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How to include material flow in job shop scheduling problem (as constraint?)?
I am reading about https://en.wikipedia.org/wiki/Job-shop_scheduling and https://en.wikipedia.org/wiki/Optimal_job_scheduling. Such scheduling is possible if we know the number (amount) of operations (...
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Lexicographic flow property and consequences
I am struggling with the understanding of the (quite famous) paper on lexicographical flows:
Maximal, Lexicographic, and Dynamic Network Flows - by Edward Minieka
...
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4
votes
1
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687
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pyomo/ipopt: nonlinear network optimization not converging
The question (very short version)
Why can I not decrease the lower boundary for the decision variable model.v_dot (see implementation) below 30 ? As soon as I do so,...
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2
votes
1
answer
126
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Advanced Transportation optimization problem
I'm trying to explore OR problems and wanted to know what algorithm fits here.
Consider fuel stations with lithium ion battery that service replacing battery at each refuel ( you replace your batters ...
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3
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0
answers
183
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Multi-commodity (Integral) flow problem with unit demand; complexity
It seems to me that a multi-commodity flow problem should be treated differently when the commodity demand constraint is an equivalence and not a lower-bound. Consider a unit demand. Apparently, in ...
- 561
3
votes
1
answer
127
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Extreme points for capacitated flow polytope
Given a network as a directed acyclic graph with a source and sink, and non-negative edge capacities, I am interested in the extreme source-sink flows. More formally, I am interested in a ...
- 1,458
4
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1
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185
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Problems modeling a constraint in network design problem
I'm working on a network design problem where the objective is to minimise the network design cost. Given a graph G = (V, E) and a set of point-to-point demands K, the task is to route the demands and ...
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4
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1
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570
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Max-flow of undirected graph
I know that a max flow problem for undirected graphs has a standard reduction to directed graphs in order to apply Ford–Fulkerson algorithm and getting a feasible solution.
Here's my doubt. An ...
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1
answer
808
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Best way to add dummy to transportation problem? Zero cost will be always chosen first?
I know that an unbalanced transportation problem could be made a balanced transportation problem by adding a dummy node which equals the difference between demand and supply.
In literature, dummy ...
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