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6 views

Inter-neighbor resistance on triangular prism

Given a triangular prism of infinite length along the X direction. A graph is formed with the set of nodes all the points on an edge of the prism with integer values of X, and the with each node ...
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1answer
29 views

Reduce problem to max flow

I have the following question: Assume each student can borrow at most 10 books from the library, and the library has three copies of each title in its inventory. Each student submits a list of ...
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1answer
20 views

Maximum Flow - Ford Fulkerson

I tried using the Ford Fulkerson algorithm with the following question: The result I got was 25: I've been told that my solution is not correct. I was not told what the solution was however. ...
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1answer
36 views

Find $k$ non-disrupting paths from $s$ to $t$

Given the bidirectional graph $G = (V, E)$ where $V$ = set of Vertices, $E$ = set of Edges; given source node $s$ and destination node $t$. Let $A_i$ ($i = 1, 2,\ldots l$) be the subset of vertices ...
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11 views

How do you update primal flow and dual slacks with dual network flow?

Heres the problem Heres my attempt The leaving arc is arc(d,b) since it is negative, now arc(d,b) = 0 The entering arc is arc(g,e) since it is lowest primal flow and in opposite direction of ...
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0answers
22 views

Prove a problem about Networks(in graph theory)

$S$ and $T$ are two subsets of $V(N)$, which is the set of vertices in network N. Let $S^c$ denotes the complement of $S$ and $[S,S^c]$ be the set of arcs starting in $S$ and finishing in $S^c$. If ...
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0answers
21 views

How do you balance a network flow?

My book says inflow(k) − outflow(k) = demand(k) = −supply(k) So for example, the demand at node a would be -41. summation of inflow = 6-1 = 5 summation of outflow = 32-9+6 = 29 5 - 29 = -24 This ...
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1answer
34 views

Some help with understanding Fulkerson algorithm for maximum flow

I'm learning flow networks. I learned Fulkerson algorithm, but there exists one point that is difficult for me. Sorry for image, but I think this is best the way I can explain my problem. This is an ...
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1answer
32 views

Network simplex method, leaving and entering variables

Could someone give me a hint on this question, which is a past exam question: Under what circumstances will an entering variable in the network simplex method be the same as the leaving variable? ...
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0answers
13 views

Flow reduction by removing a set of k edges

I am trying to find an algorithm which recieves as input: 1) a Flow network N(G,c,s,t) in which the capacity of an edge is either 0 or 1 (i.e. Exists or not). 2) a positive integer k The output ...
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1answer
30 views

Need help with minimum cost network flow problems

Consider the tree solution for the following minimum cost network flow problem: The numbers on the tree arcs represent primal flows while numbers on the nontree arcs are dual slacks. (a) Using the ...
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2answers
37 views

Spanning Tree, Network Modelling

I'm developing some software at the moment for voip communications (broadcast style comms, think ventrilo or teamspeak) between multiple users without a central server (send voice to server, server ...
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1answer
19 views

How to find a max flow in a flow network

I'm trying too many days to find an answer for this question with no success, so I hope you can help me. Let's say I have the following flow network: ...
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2answers
58 views

What is the difference between maximal flow and maximum flow?

I have tried a lot on internet, but I am unable to get a good answer on the difference between maximal and maximum flow in case of network flow. Anybody has an idea? with example would be really ...
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1answer
53 views

Enquiry to network flow

Could anyone advise me on how to find a feasible flow to the following graph so that the edges $(2,5), (4,5), (6,5),(6,7)$ are saturated? This means, I have to formulate the network flow as a linear ...
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1answer
45 views

Min-Cost-Flow Problem

Given a directed graph $G = (V,E)$ with a cost function $\gamma: E \to \Bbb R_{\geq 0}$ and two vertices $u,v \in V$. How to reduce the problem of finding a directed path from $u$ to $v$ with minimum ...
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0answers
11 views

transforming matrix data (enviornmental monitoring) into network (graph) structure

I have the following matrix of data from different locations (column 1), different stations (column 2) for different parameters (cols 3-9). The 0 values are missing data. 906 1 10 8 0 0 0 ...
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2answers
84 views

Real world application of dominating set?

can anyone tell me about the application of vertex coloring problem and algorithm for vertex color problem in graph or networks.
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1answer
37 views

the source and the sink have a maximum capacity

Consider a variant of max-flow networks in which all vertices different from the source and the sink have a maximum capacity. As we know, Such a network can be transformed into a usual max-flow ...
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1answer
50 views

Given a max flow on a graph, how do you determine the actual edges that belong to the minimal cut?

After applying an algorithm (like Ford-Fulkerson) that gives you the max flow over a graph $G(V,E)$, how do you determine the actual edges that belong to the minimal cut (recall the Max Flow/ Min Cut ...
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1answer
278 views

Finding the max flow of an undirected graph with Ford-Fulkerson

Given the following undirected graph, how would I find the max-flow/min-cut? Now, I know that in order to solve this, I need to redraw the graph so that it is directed as shown below. However, ...
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1answer
62 views

Help with linear algebra network flow (picture)

I've been stuck on this problem for hours. I keep starting and stopping because I'm not exactly sure what I'm doing. The examples the teacher worked in class were much more straight forward. If ...
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0answers
25 views

Proof of strong connectednes in digraphs by using maximum flow

G= (V,E) is strongly connected digraph if it has a directed path from i to j for every i,j in V. I want to prove that: G is strongly connected <=> every (S,T) cut in G has at least one arc in each ...
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0answers
24 views

Jackson network, steady state

My question is below: Consider a network of n queues with a Poisson arrival process of parameter t from outside the network, and independent exponentially distributed service times of ...
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0answers
37 views

Potential values of minimum cost maximum flow algorithm

I have a simple directed graph $G(V,E)$ that has a source $s$ and sink $t$. Each edge $e$ of $G$ has positive integer capacity $c(e)$ and positive integer cost $a(e)$. I am trying to find the minimum ...
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1answer
35 views

Flow network: Source with in degree and sink with out degree

I have a flow network G with a single source s and a single sink t, but out-degree(t) is not 0 and in-degree(s) is not 0. Does removing all the edges leaving t and/or entering s change the capacity ...
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0answers
42 views

Minimum u-v cuts

I am working on the following problem: Consider the $G=(V,E)$ and let $w:E \rightarrow \mathbb{R^+}$ be an assignment of nonnegative weights to its edges. Given $u,v \in V$, let f(u,v) be the weight ...
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1answer
80 views

Spanning Tree - Equivalent Properties

I am working on the following problem: Suppose that $T$ is a spanning tree of a graph $G$, with an edge cost function $c$. Let $T$ have the cycle property if for any edge $e' \not \in T, c(e') \geq ...
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1answer
36 views

Finding maximum flow of directed network with two inputs

I am given a directed network graph with three fixed verticess where two of these are "inputs" and and one is the "sink". I'm asked to find the maximal flow through the network. How should go about ...
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0answers
26 views

Network component detection

Suppose I have a (directed) graph with nonnegative edge weights. I would like to separate the graph into what you might call "$\epsilon$-components", that is, a partition $\{ V_i \}$ of the set $V$ of ...
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1answer
416 views

Proof of König's theorem

Let $G=(V,E)$ be a graph. $H\subseteq V$ is called a vertex cover of $G$ iff $(u,v)\in E\Rightarrow u\in H\vee v\in H$. Now let's assume $G$ is bipartite, i.e. $V=V_1 \cup V_2$ and $E\subseteq ...
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1answer
46 views

The Dons Problem: Minimizing the time for complete diffusion of information [duplicate]

A friend of mine asked me this question recently. He might have heard from somewhere else, but that's the extent of my background on this problem. It might have a completely different name, and I ...
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1answer
68 views

Flow Graphs: Why do you need the symmetry property of a graph?

$$\begin{gather} f(u,v) \le c(u,v) \tag{Capacity constraint} \\ f(u,v) = -f(v,u) \tag{Symmetry} \\ \sum_{\large{v \in V, v \ne s,t}} f(u,v) = 0 \tag{Conservation of flow} \end{gather}$$ When you are ...
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0answers
49 views

max flow/ min cut

Im trying to work out a flow of size 10 for the commodity network below (using Ford and Fulkerson algorithm). When working out the flow, would this be an acceptable solution: Where 2 + 2 + 2 + 2 ...
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0answers
146 views

How to show that union and intersection of min cuts in flow chart is also a min cut

The proof of this is everywhere skipped and said to be collorary of Ford-Fulkerson theorem. It's usually something like: Let $A$ and $B$ be low cuts of a flow chart. Then $A \cup B$ and $A \cap B$ ...
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0answers
35 views

Graph theory: Linking graph characteristics and minimal cut

I'm currently working on a research involving Graph theory. More specifically, I would like to make an analytical or theoretic connection between different characteristics of the graph (e.g. size, ...
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1answer
169 views

Duality of max-flow and min-cut: when infinite capacity exists

I am wondering if the celebrated duality between max-flow and min-cut actually tolerates infinite valued capacities. Here is a simple example where it seems not: source s, sink t, five other nodes a, ...
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1answer
42 views

what is a flow in the context of the Ford-Fulkerson algorithm?

I am learning about the Ford Fulkerson algorithm, but having a hard time getting an intuitive feel for what a "flow" is. Is the "flow" the amount that travels between two adjacent nodes on a graph? Or ...
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0answers
58 views

Prime-Dual Algorithm Proof for Transshipment Problem

Consider an example of Transshipment Problem (TP) with a directed graphy $D=(N,A)$ such that $b(N)=0$ ($b$ are node demands). Suppose that one of the iteration from Dijkstra's algorithm finds that a ...
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1answer
220 views

Determine whether a graph has a unique max flow

Is there a characterization result/some sufficient conditions that ensure that a graph has a unique max flow? Note that it does not say anything about the min-cuts: a path with all edges having ...
0
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1answer
71 views

Decomposing flows on a graph as a sum of cycle flows and source flows

I am reading a paper where they say the following is "easy" but I can't seem to see why. Let $G$ be a finite undirected graph on an edge set $V$ and let $E$ be its set of oriented edges (i.e. each ...
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1answer
66 views

Prove / Disprove: If the Residual Graph $G_f$ Contains no Path from $u$ to $v$ then $e$ Crosses Some Minimum Cut

Let $G = (V,E)$ be a flow network. Let $e = (u,v)$ be an edge in $E$ and let $f$ be a maximum flow in $G$. Prove or Disprove: If the residual graph $G_f$ contains no directed path from $u$ to ...
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1answer
66 views

Network's flow - a couple of issues

There are three requirements for the path to be a flow - capacity constraints, skew symmetry, and the flow conservation ( http://en.wikipedia.org/wiki/Flow_network ). Ok, but what if the network ...
2
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2answers
69 views

What would a Tutte Polynomial =0 represent?

So I'm working on proving (via contradiction) that the flow number $\phi(G)$ of a bridgeless graph $G$ is always defined. I'm using the flow polynomial, and I got to a point where I have $0=T(0,1-u)$. ...
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0answers
84 views

Which cut does the “minimum cut” refer to?

My course notes give the following definitions; could someone please verify that the last definition is non-standard? (I've spent all evening googling, and isn't "minimum cut" a concept related to cut ...
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0answers
131 views

Are edge cuts, vertex cuts, and cut sets all variously called “cuts”?

I've seen "cut" being used to refer to all three, in different places, and sometimes in the same book. Which does "cut" most commonly refer to? p.s. I am aware that "cut" itself can be defined to ...
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1answer
867 views

Do “cut set” and “edge cut” mean the same thing?

The definitions I have are: A cut set of a graph $G$ induced by a partition of $G$'s vertices into sets $X$ and $Y$ is the set of all edges with one endpoint in $X$ and another endpoint in ...
2
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0answers
114 views

Max - Flow and Min - Cut, Minimize the number of visible boxes

Suppose that you are given a set of boxes, with each box as a rectangular parallelepiped with side lengths as (i1, i2, i3). And each side length is between half a meter and one meter. How should a ...
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0answers
175 views

Using maximum flow algorithm to check existence of a matrix

Using the maximum flow algorithm, I have to determine if there exists a $3\times 3$ matrix $P$ (such that all elements are $\geq 0$). I'm given: The maximum values of the row sums The column sums ...
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0answers
141 views

Two-commodity minimum cost flow with antisymmetric costs

I'm looking at a minimum-cost flow problem in directed acyclic graphs. We are given a DAG plus a cost function that maps an edge to a real-valued cost, and a capacity function that maps an edge to a ...