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.

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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 ...
Mathematician....'s user avatar
0 votes
1 answer
71 views

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, ...
Last_Mile's user avatar
2 votes
2 answers
120 views

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 ...
dieter's user avatar
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0 answers
49 views

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^...
orpanter's user avatar
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0 answers
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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 ...
user2705034's user avatar
3 votes
0 answers
66 views

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 ...
Matheus Diógenes Andrade's user avatar
1 vote
2 answers
236 views

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 ...
Carmen González's user avatar
4 votes
0 answers
646 views

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-...
Pia MiA's user avatar
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2 votes
2 answers
229 views

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 ...
Pia MiA's user avatar
  • 392
3 votes
2 answers
114 views

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 ...
Cris's user avatar
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3 votes
2 answers
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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 ...
J. Alan's user avatar
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2 votes
1 answer
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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 ...
endeavor's user avatar
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2 votes
1 answer
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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 ...
Daniele Cuomo's user avatar
5 votes
1 answer
172 views

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 ...
Kuifje's user avatar
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1 vote
0 answers
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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 ...
PrashanthVajjhala's user avatar
3 votes
1 answer
119 views

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 ...
Mike's user avatar
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3 votes
1 answer
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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 ...
Fabian's user avatar
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1 answer
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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 ...
Daniele Cuomo's user avatar
6 votes
1 answer
370 views

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 ...
Raghav Thakar's user avatar
-1 votes
1 answer
85 views

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 ...
Harun Gül's user avatar
1 vote
1 answer
143 views

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 ...
orpanter's user avatar
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2 votes
1 answer
573 views

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 ...
Fernando Martinez's user avatar
0 votes
1 answer
107 views

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 ...
Fernando Martinez's user avatar
1 vote
0 answers
143 views

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 ...
Emma Kuttler's user avatar
3 votes
4 answers
492 views

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 ...
Emma Kuttler's user avatar
4 votes
2 answers
168 views

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-...
Emma Kuttler's user avatar
1 vote
0 answers
502 views

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 ...
Emma Kuttler's user avatar
3 votes
2 answers
465 views

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 ...
themlchic's user avatar
2 votes
2 answers
212 views

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}...
Devita J's user avatar
6 votes
2 answers
293 views

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. ...
anerjee's user avatar
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3 votes
0 answers
132 views

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 ...
asdf's user avatar
  • 105
3 votes
0 answers
99 views

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 ...
Suleyman Karabuk's user avatar
2 votes
1 answer
303 views

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 ...
Bree's user avatar
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1 vote
0 answers
22 views

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 ...
Daniele Cuomo's user avatar
3 votes
1 answer
89 views

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. ...
Daniele Cuomo's user avatar
5 votes
1 answer
152 views

(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 ...
Daniele Cuomo's user avatar
1 vote
0 answers
55 views

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. ...
Daniele Cuomo's user avatar
1 vote
0 answers
44 views

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 ...
Daniele Cuomo's user avatar
1 vote
0 answers
22 views

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)?
Daniele Cuomo's user avatar
1 vote
0 answers
27 views

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: ...
Daniele Cuomo's user avatar
3 votes
1 answer
423 views

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 ...
Daniele Cuomo's user avatar
1 vote
2 answers
395 views

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 (...
TomR's user avatar
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2 votes
0 answers
31 views

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 ...
Daniele Cuomo's user avatar
4 votes
1 answer
687 views

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,...
Khalilbs's user avatar
2 votes
1 answer
126 views

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 ...
themlchic's user avatar
3 votes
0 answers
183 views

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 ...
Daniele Cuomo's user avatar
3 votes
1 answer
127 views

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 ...
batwing's user avatar
  • 1,458
4 votes
1 answer
185 views

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 ...
crypto's user avatar
  • 143
4 votes
1 answer
570 views

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 ...
Daniele Cuomo's user avatar
4 votes
1 answer
808 views

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 ...
learnPyt's user avatar