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How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Comparison and Implementation of Algorithms in Maximum Flow Problem J.Gui.

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Presentation on theme: "How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Comparison and Implementation of Algorithms in Maximum Flow Problem J.Gui."— Presentation transcript:

1 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Comparison and Implementation of Algorithms in Maximum Flow Problem J.Gui December 2005 CS 721

2 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Introduction What is a flow network about? Why maximum flow problem? Origin and History The origin of maximum flow problem History of important algorithms The maximum flow algorithms The Ford-Fulkerson algorithm (1956) Karzanov’s Algorithm(1973) MPM Algorithm (1978) Comparison of algorithms Implementation of Ford-Fulkerson Implementation Problems in implementation introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson Jie Gui, McMaster University Comparison and Implementation of Algorithms in Maximum Flow Problem CS 721

3 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 source vertex s, sink vertex t; What is a flow network about? Why maximum flow problem? Jie Gui, McMaster University s t 1 2 3 4 a directed graph G = (V, E); Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

4 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 source vertex s, sink vertex t; What is a flow network about? Jie Gui, McMaster University s t 1 2 3 4 a directed graph G = (V, E); 2 1 5 4 6 7 3 a nonnegative capacity c(u, v); Comparison and Implementation of Algorithms in Maximum Flow Problem What is a flow network about? Why maximum flow problem? introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

5 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Capacity 2:32:3 1:11:1 2:62:6 2:22:2 -1:7 1:41:4 2:52:5 source vertex s, sink vertex t; What is a flow network about? Jie Gui, McMaster University s t 1 2 3 4 a directed graph G = (V, E); 3 2 5 4 6 7 1 a nonnegative capacity c(u, v); Network Flow? A flow on G is a function f : V × V→ satisfying… Capacity constraint: For all u, v ∈ V, f (u, v) ≤ c(u, v). Capacity Skew symmetry: For all u, v ∈ V, f (u, v) = –f (v, u). Capacity Flow conservation: For all u ∈ V –{s, t}, Comparison and Implementation of Algorithms in Maximum Flow Problem What is a flow network about? Why maximum flow problem? introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

6 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 V 4:5 2:3 Why maximum flow problem? What is a flow network? Why maximum flow problem? Jie Gui, McMaster University s 1 t 2 3 4 4:6 ? ? 4 + 2 > 1 (capacity limit) ‘BOTTLENECK’ 1 4:5 2:3 ?:1 1 Maximum-flow problem: Given a flow network G, find a flow of maximum value |f| on G. ?:1 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

7 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Comparison and Implementation of Algorithms in Maximum Flow Problem The origin of network flow problem Simplex method linear optimization Klee-Minty cube interior point methods Jie Gui, McMaster University Although accredited to Dantzig in the early 50’s, the maximum flow problem’s predecessors can be shown in written materials as early as the 1930s. The transportation issue, which later evolved into the maximum flow problem as transportation routes became more complex, was studied extensively in the Soviet Union by the National Commissariat of Transportation. The Commissariat, A.N. Tolstoi, examined the optimal solution for shipping cargo throughout the Soviet Union via the railroad system with multiple sources of product and many individual destinations. Tolstoi worked with a network of 10 sources, 68 destinations, and 155 links among the sources and destinations space What makes Tolstoi’s examinations not a “true” maximum flow problem is that he was working under the condition that the graph given was a circular graph along the railway line with multiple sources and destinations. This allowed for “the optimum solution to be readily obtained by considering the difference of two sums of costs. He called this phenomenon circle dependency.” This circular path transportation problem gave birth to the maximum flow problem. space Space space introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

8 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University The history of maximum flow algorithms Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

9 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University The Maximum Flow algorithms Three algorithms introduced today, Ford-Fulkerson Algorithm (1956) Karzanov’s Algorithm (1973) MPM Algorithm (1978) First maximum flow algorithm, Max-Flow Min-Cut Theorem, no upper bound for time complexity. Using layered network to find the maximum flow by advancing preflow and balancing it, the time complexity is O(V 3 ). Using layered network to find the maximum flow by finding a potential flow vertex, using pushing and pulling back process, the time complexity is O(V 3 ). Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

10 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) The first algorithm for the network flow problem was given by Ford and Fulkerson. BIG PICTURE: The algorithm is iterative. Initially, all edge flows are set to zero. To improve the current flow, we try to find augmenting paths along which we could push more flow in the residual network. If the no augmenting path could not be found, the current flow in the network is the maximum flow. IMPORTANT DEFINITIONS: Cuts -- A cut (S, T) of a flow network G = (V, E) is a partition of V such that s ∈ S and t ∈ T. If f is a flow on G, then the flow across the cut is f (S, T). Augmenting Paths -- Any path from s to t in G f is an augmenting path in G with respect to f. The flow value can be increased along an augmenting path p by c f ( p) = min {c f (v, u )}. (v, u ) ∈ p Residual Network -- Let f be a flow on G = (V, E). The residual network G f (V, E f ) is the graph with strictly positive residual capacities c f (u, v) = c(u, v) – f (u, v) > 0. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

11 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) 0:20:2 0:10:1 0:10:1 0:20:2 0:10:1 0:10:1 0:10:1 s t 1 2 3 4 STEP 1: Labeling Process Vertex Status: Unlabeled; Labeled and unscanned; Labeled and scanned; every vertex v gets a label (u, +/-, z) Labels: u -- the vertex that was being scanned when v was labeled.; +/- -- indicates the direction of the useful edge e connect u and v; z – maximum possible capacity of flow can be increased to v through any augmenting path found previously. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

12 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) 0:20:2 0:10:1 0:10:1 0:20:2 0:10:1 0:10:1 0:10:1 s 1 2 3 4 t STEP 1: Labeling Process every vertex v gets a label (u, +/-, z) BFS – Edmonds Karp (-∞, +, ∞) (s, +, 2) (s, +, 1) (1, +, 1) (2, +, 1) The order of labeling ● t is assigned a label; When we stop? ● t has no label, no more label can be assigned to any vertex; augmenting path found go to STEP 2; flow is maximum! Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

13 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) 0:20:2 0:10:1 0:10:1 0:20:2 0:10:1 0:10:1 0:10:1 STEP 2: Flow Augmentation Process augment the flow function from vertex t by value z + -- Increase flow value of the forward edge; (-∞, +, ∞) (s, +, 2) (s, +, 1) (1, +, 1) (2, +, 1) Augmentation s 1 2 3 4 t - -- Decrease flow value of the backward edge; 1:11:1 1:11:1 1:11:1 Erase all labels; Go to STEP 1; When finished Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

14 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) 0:20:2 0:10:1 0:20:2 0:10:1 (-∞, +, ∞) (s, +, 2) (2, -, 1) (1, +, 1) (3, +, 1) (4, +, 1) s 1 2 3 4 t 1:11:1 1:11:1 1:11:1 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

15 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) 1:21:2 1:11:1 1:21:2 1:11:1 s 1 2 3 4 t 1:11:1 0:10:1 1:11:1 Max-Flow Min-Cut Theorem 1. | f | = min{ c (S, T) }for all cuts (S, T) in G. 2. f is a maximum flow. 3. f admits no augmenting paths. s → 3 → 2 → t s → 1 → 4 → t Maximum Flow is 2 ! Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

16 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Ford-Fulkerson algorithm (1956) ANALYSIS: The time complexity of original FF algorithm depends on the number of the edges and vertices in the whole network and the value of the maximum flow function |f*|. The maximum flow value is equal to the minimum cut capacity which is an integer. This algorithm needs at most |f*| flow augmenting paths where each flow- augmenting path needs at most O(V 2 ) steps. Since |f*| is not known in the beginning, we do not have a upper bound in terms of vertices and edges. 0:10000 s 1 2 3 0:10:1 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

17 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) BIG PICTURE: Try to force as much preflow as possible, from the source vertex s, through the edges of the layered network, to the sink vertex t. This process leaves some vertices v with excess flow. In order to correct this, the algorithm runs like a stack, beginning from the last layer of the network to rebalance those vertices, and then try to push more flow again in the same layer, those edges connect to the vertices have been balanced and could not be used again will be blocked (closed), so that no more flow can pass through them again. The iteration of push/rebalance will be terminates when vertex s is reached, leaving the flow in the network maximum. The main steps are: STEP 0: Construct Layered Network STEP 1: Push PreFlow STEP 2: Rebalance PreFlow Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

18 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) 4 t 1 2 3 s Layered Network Layer 1Layer 2 Layer 3 Layer 4 The layer index correspond to the length shortest path if the length of every edge in the network is defined to 1. Therefore no more backwards edge exists. (Formatting the network) 4 + 2 > 1 (capacity limit) ‘Unbalance’ 1 4:5 2:3 1:1 1 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

19 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 1: Push Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 8, [8] 5, [5] 4, [4] 5, [5] 6, [6] 2, [7] 2, [4] Try to push as much flow as every edge could within its capacity, regardless the flow conservation property Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

20 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 2: Rebalance Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 8, [8] 5, [5] 4, [4] 5, [5] 1, [6] 2, [7] 2, [4] In layer 3, vertex 2 should be balanced. The flow on edge (1-2) will be changed to 1. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

21 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 2: Rebalance Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 8, [8] 5, [5] 4, [4] 5, [5] 1, [6] 2, [7] 2, [4] Edge (3-2), (2- t), (1-2) are marked closed. Vertex 2 is blocked. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

22 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 1: Pushing Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 8, [8] 5, [5] 4, [4] 5, [5] 1, [6] 7, [7] 4, [4] Since edge (1- 4) and (4-t) are still open, there will be another preflow pushing carried out. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

23 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 2: Rebalance Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 8, [8] 5, [5] 4, [4] 5, [5] 1, [6] 4, [7] 4, [4] Vertex 4 has been balanced again and blocked, and edge (4-t), (1-4) has been marked closed Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

24 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) STEP 2: Rebalance Preflow 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 5, [8] 4, [5] 4, [4] 5, [5] 1, [6] 4, [7] 4, [4] Since no more preflow can be pushed at layer 3. Rebalance will run again at Layer 2. Vertex 3 and Vertex 1 should be rebalanced. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

25 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) Algorithm terminated, Maximum Flow Achieved! The maximum flow we have is 9. 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 5, [8] 4, [5] 4, [4] 5, [5] 1, [6] 4, [7] 4, [4] Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

26 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Karzanov’s Algorithm (1973) ANALYSIS: Karzanov’s algorithm for maximum flow in a layered network takes O(V 2 ) time, since there might be at most n-1 push-rebalance phases, the total time is O(V 3 ). Broken into: 1. If the flow on any edge is reduced, then the edge will be closed right after, hence the total number of flow reduction is bounded by O(E). 2. If the edge is not saturated, the flow is increased but not to its capacity, this will keep happening for n-1 times, then n-2 times until the capacity is reached. Therefore, the total time complexity of this situation will be (n-1) + (n-2) …+ 1 = O(V 2 ). 3. Therefore for one phase the total time would be O(E) + O(V 2 ) = O(V2), for n phase, there will be at most O(V 2 ) Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

27 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) BIG PICTURE: This is algorithm inroduced by Malhotra, Pramodh-Kumar and Maheshwari. This algorithm has mainly four steps as following: STEP 0: Setup layered network (totally the same as in Karzanov’s algorithm) STEP 1: Find out the vertex v inside the layered network, which has potential flow.----p*. STEP 2: Push the potential flow through all the layers after the current layer that v is in, if vertex v is not the sink of the network. STEP 3: Pull back potential flow to the layers in the front with the same process. Then, remove all vertices that has a potential flow of 0 together with the edges connect to it, and update the main network with the result. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

28 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 0, [8] 0, [5] 0, [4] 0, [5] 0, [6] 0, [7] 0, [4] STEP 1:The Potential Flow Selection To any vertex in the network, the potential flow is defined as: min{sum(incoming edges’ residual capacity), sum(outgoning edges’s residual capacity)} 13 4 8 4 59 Obviously, the minimum potential flow of the whole network is 4. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

29 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 0, [8] 0, [5] 4, [4] 4, [5] 0, [6] 0, [7] 0, [4] STEP 2: Push the potential flow Select vertex 3 to be the start point for the first iteration. The augment flow of 4 unit will be push ahead layer by layer until sink t will be reached. 13 4 8 4 59 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

30 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 0, [8] 4, [5] 4, [4] 4, [5] 0, [6] 0, [7] 0, [4] STEP 3: Pull the potential flow The same amount of potential flow will be pulled back through layers until source s is reached. When finished the latest potential flow of vertex 3 is 0, hence vertex 3 and edges connect to it will be remove from the layered network. 13 0 8 4 59 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

31 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 0, [8] 4, [5] 4, [4] 4, [5] 0, [6] 0, [7] 0, [4] STEP 1: The Potential Flow Selection The potential flow of the network will be recalculated based upon the updated network. No consideration of the removed vertices and edges will be taken. The new potential flow is selected from vertex 2, since it has the least in value, which is 1. 8 0 8 4 15 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

32 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 1, [8] 4, [5] 4, [4] 5, [5] 1, [6] 0, [7] 0, [4] After the 2nd phase… Since the vertex 2 has been removed from the network, edges (1-2) and (2-t) are also removed, so that they would never be used again. The next minimum potential flow is chose from vertex 4. 7 0 7 4 04 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

33 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) 4 t 1 2 3 s Layer 1Layer 2 Layer 3 Layer 4 5, [8] 4, [5] 4, [4] 5, [5] 1, [6] 4, [7] 4, [4] After the 3rd phase… Since the vertex 4 has been removed from the network, edges (1-4) and (4-t) are also removed, so that they would never be used again. Now the algorithm terminates, since the potential flow of sink t has become 0, any further process will cause t being remove from the network. Therefore the maximum flow has been reached. 3 0 3 0 00 Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

34 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University MPM Algorithm (1978) ANALYSIS: The time for MPM algorithm to compute out maximal flow in one phase takes O(V 2 ) time, since there might be at most n-1 push/pull phases, the total time is O(V 3 ). Broken into: 1. The time to locate the minimum potential flow takes at most O(V 2 ). 2. push/pull process in the layered network will takes up to O(V 2 ). 3. Since every edge will only be saturated once, so the time is bounded by O(E); 4. The number of execution phases will be bounded by O(V). Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

35 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Comparisons among the three algorithms ANALYSIS: 1. Ford-Fulkerson algorithm is important and well-known for its way of solve the problem rather than the speed of the original algorithm, it is not actually polynomially bounded and will fail to get the correct answer when the capacity of the edges set to irrational values. 2. In the system of residual network and augmenting path given by FF methods, it is important to solve the key point of the way it finds the shortest path from source towards sink vertex, among forward and backward edges. 3. The reason why the latter two algorithms have a much faster speed than FF is that they are both built upon the layered network that has already cleared the way to the sink vertex by guaranteeing each path is the shortest path in each layer. But they will consume more system resources to save info when implemented. 4. Though slower, FF algorithm is really easier to implement and gets a faster speed in execution particularly in smaller scaled network which has fewer vertices. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

36 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 CLASS IMPLEMENTATION The source code files for project in cs 721 are consisted of the following files: RealProblem.java=====v1.03 * This program is written to implement a real simple example of Maximum Flow Problem. GraphNetwork.java====v1.02 * This class is used to implement to structure of a graph network. MaximumFlowFF.java==v1.02 * This class is used to implement the FF algorithm. NetworkEdge.java=====v1.02 * This class is used to implement the basic properties of the edge in flow network. NetworkVertex========v1.02 * This class is used to represent the basic structure of network vertex. Jie Gui, McMaster University Implementation of Ford-Fulkerson algorithm Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

37 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 INTRODUCTION The example input for this implementation is taken from the example used in the front parts for Karzanov’s and MPM algorithms. The class that can be executed is “RealProblem.java”, in which data information for the input example is included as well. Below is a snapshot from execution… Jie Gui, McMaster University Implementation of Ford-Fulkerson algorithm Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721

38 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Problem in implementations: WEAK POINTS: 1. Since it comes out from Ford-Fulkerson algorithm, a little modification is made by using BFS, in order to get the shortest path in the network, actually from Edmonds Karp; 2. Only able to deal with the situation that the edge capacity is a irrational number. 3. Speed become slower when dealing with a larger network and when the network has many edges. Comparison and Implementation of Algorithms in Maximum Flow Problem introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson CS 721 4. The implementation is to some extend limited, particularly suitable for small scale flow network, since I have everything represented in arrays that take up much resources to store data and have a slower speed of indexing.

39 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University REFERENCES 1. A.N. Tolstoi: Methods of Finding Minimum Total Kilometrage in Cargo- Transportation Planning in Space. Transportation Planning, 1 (1930) 23- 55. Comparison and Implementation of Algorithms in Maximum Flow Problem CS 721 2. T.C. Hu. Combinatorial Algorithms. Addison Wesley, (1982) 3. T.H. Cormen, C.E. Leiserson, R.L. Rivest, and C. Stein, Introduction to Algorithms, second edition McGraw-Hill & MIT Press (2001). 4. G. Brassard and P. Bratley, Algorithmics: Theory & Practice, Prentice Hall (1988). 5. F. Harary, Graph Theory, Addison-Wesley (second edition) (1972). introduction Origin and History The maximum flow algorithms Comparison of algorithms Implementation of Ford-Fulkerson

40 How good are interior point methods? Tamás Terlaky, McMaster University, May 2005 Jie Gui, McMaster University Thank you for your time! The End Comparison and Implementation of Algorithms in Maximum Flow Problem CS 721 Speacial Thanks to Dr. Franya Franek!


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