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• When can I be sure a directed graph is acyclic?

  - by Daniel Scocco

  The definition for directed acyclic graph is this: "there is no way to start at some vertex v and follow a sequence of edges that eventually loops back to v again." So far so good, but I am trying to find some premises that will be simpler to test and that will also guarantee the graph is acyclic. I came up with those premises, but they are pretty basic so I am sure other people figured it out in the past (or they are incorrect). The problem is I couldn't find anything related on books/online, hence why I decided to post this question. Premise 1: If all vertices of the graph have an incoming edge, then the graph can't be acyclic. Is this correct? Premise 2: Assume the graph in question does have one vertex with no incoming edges. In this case, in order to have a cycle, at least one of the other vertices would need to have two or more incoming edges. Is this correct?

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• Merging similar graphs based solely on the graph structure?

  - by Buttons840

  I am looking for (or attempting to design) a technique for matching nodes from very similar graphs based on the structure of the graph*. In the examples below, the top graph has 5 nodes, and the bottom graph has 6 nodes. I would like to match the nodes from the top graph to the nodes in the bottom graph, such that the "0" nodes match, and the "1" nodes match, etc. This seems logically possible, because I can do it in my head for these simple examples. Now I just need to express my intuition in code. Are there any established algorithms or patterns I might consider? (* When I say based on the structure of the graph, I mean the solution shouldn't depend on the node labels; the numeric labels on the nodes are only for demonstration.) I'm also interested in the performance of any potential solutions. How well will they scale? Could I merge graphs with millions of nodes? In more complex cases, I recognize that the best solution may be subject to interpretation. Still, I'm hoping for a "good" way to merge complex graphs. (These are directed graphs; the thicker portion of an edge represents the head.)

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• Facebook Graph API - likes returns me an empty set...

  - by Vinch

  When I try to get all my "likes" (formerly fan pages) on Facebook Graph API, sometimes it returns me an empty set: { "data": [ ] } I tried with https://graph.facebook.com/me/likes?access_token=MY_ACCESS_TOKEN and with graph.facebook.com/vinch/likes?access_token=MY_ACCESS_TOKEN but the result is exactly the same (empty). Any idea of what it can be? I need it to know if a user likes (is fan of) a specific page.

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• Suggestions of the easiest algorithms for some Graph operations

  - by Nazgulled

  Hi, The deadline for this project is closing in very quickly and I don't have much time to deal with what it's left. So, instead of looking for the best (and probably more complicated/time consuming) algorithms, I'm looking for the easiest algorithms to implement a few operations on a Graph structure. The operations I'll need to do is as follows: List all users in the graph network given a distance X List all users in the graph network given a distance X and the type of relation Calculate the shortest path between 2 users on the graph network given a type of relation Calculate the maximum distance between 2 users on the graph network Calculate the most distant connected users on the graph network A few notes about my Graph implementation: The edge node has 2 properties, one is of type char and another int. They represent the type of relation and weight, respectively. The Graph is implemented with linked lists, for both the vertices and edges. I mean, each vertex points to the next one and each vertex also points to the head of a different linked list, the edges for that specific vertex. What I know about what I need to do: I don't know if this is the easiest as I said above, but for the shortest path between 2 users, I believe the Dijkstra algorithm is what people seem to recommend pretty often so I think I'm going with that. I've been searching and searching and I'm finding it hard to implement this algorithm, does anyone know of any tutorial or something easy to understand so I can implement this algorithm myself? If possible, with C source code examples, it would help a lot. I see many examples with math notations but that just confuses me even more. Do you think it would help if I "converted" the graph to an adjacency matrix to represent the links weight and relation type? Would it be easier to perform the algorithm on that instead of the linked lists? I could easily implement a function to do that conversion when needed. I'm saying this because I got the feeling it would be easier after reading a couple of pages about the subject, but I could be wrong. I don't have any ideas about the other 4 operations, suggestions?

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• algorithm to use to return a specific range of nodes in a directed graph

  - by GatesReign

  I have a class Graph with two lists types namely nodes and edges I have a function List<int> GetNodesInRange(Graph graph, int Range) when I get these parameters I need an algorithm that will go through the graph and return the list of nodes only as deep (the level) as the range. The algorithm should be able to accommodate large number of nodes and large ranges. Atop this, should I use a similar function List<int> GetNodesInRange(Graph graph, int Range, int selected) I want to be able to search outwards from it, to the number of nodes outwards (range) specified. So in the first function, I expect it to return the nodes placed in the blue box. The other function, if I pass the nodes as in the graph with a range of 1 and it starts at node 5, I want it to return the list of nodes that satisfy this criteria (placed in the orange box)

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• Generic Adjacency List Graph implementation

  - by DmainEvent

  I am trying to come up with a decent Adjacency List graph implementation so I can start tooling around with all kinds of graph problems and algorithms like traveling salesman and other problems... But I can't seem to come up with a decent implementation. This is probably because I am trying to dust the cobwebs off my data structures class. But what I have so far... and this is implemented in Java... is basically an edgeNode class that has a generic type and a weight-in the event the graph is indeed weighted. public class edgeNode<E> { private E y; private int weight; //... getters and setters as well as constructors... } I have a graph class that has a list of edges a value for the number of Vertices and and an int value for edges as well as a boolean value for whether or not it is directed. The brings up my first question, if the graph is indeed directed, shouldn't I have a value in my edgeNode class? Or would I just need to add another vertices to my LinkedList? That would imply that a directed graph is 2X as big as an undirected graph wouldn't it? public class graph { private List<edgeNode<?>> edges; private int nVertices; private int nEdges; private boolean directed; //... getters and setters as well as constructors... } Finally does anybody have a standard way of initializing there graph? I was thinking of reading in a pipe-delimited file but that is so 1997. public graph GenereateGraph(boolean directed, String file){ List<edgeNode<?>> edges; graph g; try{ int count = 0; String line; FileReader input = new FileReader("C:\\Users\\derekww\\Documents\\JavaEE Projects\\graphFile"); BufferedReader bufRead = new BufferedReader(input); line = bufRead.readLine(); count++; edges = new ArrayList<edgeNode<?>>(); while(line != null){ line = bufRead.readLine(); Object edgeInfo = line.split("|")[0]; int weight = Integer.parseInt(line.split("|")[1]); edgeNode<String> e = new edgeNode<String>((String) edges.add(e); } return g; } catch(Exception e){ return null; } } I guess when I am adding edges if boolean is true I would be adding a second edge. So far, this all depends on the file I write. So if I wrote a file with the following Vertices and weights... Buffalo | 18 br Pittsburgh | 20 br New York | 15 br D.C | 45 br I would obviously load them into my list of edges, but how can I represent one vertices connected to the other... so on... I would need the opposite vertices? Say I was representing Highways connected to each city weighted and un-directed (each edge is bi-directional with weights in some fictional distance unit)... Would my implementation be the best way to do that? I found this tutorial online Graph Tutorial that has a connector object. This appears to me be a collection of vertices pointing to each other. So you would have A and B each with there weights and so on, and you would add this to a list and this list of connectors to your graph... That strikes me as somewhat cumbersome and a little dismissive of the adjacency list concept? Am I wrong and that is a novel solution? This is all inspired by steve skiena's Algorithm Design Manual. Which I have to say is pretty good so far. Thanks for any help you can provide.

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• .NET implementation of planarity testing

  - by DixonD

  Is there any .NET implementation of any planarity testing algorithm like Boyer-Myrvold's or anyone else? I looked through the web but I didn't manage to find

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• How to represent a graph with multiple edges allowed between nodes and edges that can selectively disappear

  - by Pops

  I'm trying to figure out what sort of data structure to use for modeling some hypothetical, idealized network usage. In my scenario, a number of users who are hostile to each other are all trying to form networks of computers where all potential connections are known. The computers that one user needs to connect may not be the same as the ones another user needs to connect, though; user 1 might need to connect computers A, B and D while user 2 might need to connect computers B, C and E. Image generated with the help of NCTM Graph Creator I think the core of this is going to be an undirected cyclic graph, with nodes representing computers and edges representing Ethernet cables. However, due to the nature of the scenario, there are a few uncommon features that rule out adjacency lists and adjacency matrices (at least, without non-trivial modifications): edges can become restricted-use; that is, if one user acquires a given network connection, no other user may use that connection in the example, the green user cannot possibly connect to computer A, but the red user has connected B to E despite not having a direct link between them in some cases, a given pair of nodes will be connected by more than one edge in the example, there are two independent cables running from D to E, so the green and blue users were both able to connect those machines directly; however, red can no longer make such a connection if two computers are connected by more than one cable, each user may own no more than one of those cables I'll need to do several operations on this graph, such as: determining whether any particular pair of computers is connected for a given user identifying the optimal path for a given user to connect target computers identifying the highest-latency computer connection for a given user (i.e. longest path without branching) My first thought was to simply create a collection of all of the edges, but that's terrible for searching. The best thing I can think to do now is to modify an adjacency list so that each item in the list contains not only the edge length but also its cost and current owner. Is this a sensible approach? Assuming space is not a concern, would it be reasonable to create multiple copies of the graph (one for each user) rather than a single graph?

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• Graphviz or Dynagraph for Graph-manipulation Program?

  - by noahlavine

  I'm looking into writing a program that will show a graph to the user. The graph will change over time (the user should be able to right-click on a graph item and ask for more detail, which will pop out new bits of the graph), and the user might be able to drag parts of the graph around. I would ideally also like to be able to specify the relative layout of certain parts of the graph myself while leaving the overall layout up to a library, but that's not essential. I'm trying to decide on a graph layout library to use. As far as I can tell, the two leading candidates are Graphviz and Dynagraph. The Dynagraph website suggests that Graphviz is for drawing static graphs, and that Dynagraph was forked from Graphviz and contains algorithms for graphs that will be updated. It has a sample program called Dynasty that does exactly what I want. However, the Graphviz site contains an example program called Lefty which seems to do exactly what I want. Graphviz also seems to be much more widely used, judging by Google (and SO) results. Finally, I'd like to code the GUI part in a language like Python or Scheme, which makes me a bit hesitant to use C++ because I understand it's harder to interface that to interpreters. So my question is, which library is better for what I'm trying to do? Do they both have strong and weak points? Has one of them actually ceased development and is just leaving its website up to confuse me? (I've seen http://stackoverflow.com/questions/464000/simple-dynamic-graph-display-for-c and http://stackoverflow.com/questions/2376987/open-source-libraries-to-design-directed-graphs, but I can't tell whether they're right about the Graphviz or Dynagraph choice because of Lefty and also the language issue.)

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• Scalable / Parallel Large Graph Analysis Library?

  - by Joel Hoff

  I am looking for good recommendations for scalable and/or parallel large graph analysis libraries in various languages. The problems I am working on involve significant computational analysis of graphs/networks with 1-100 million nodes and 10 million to 1+ billion edges. The largest SMP computer I am using has 256 GB memory, but I also have access to an HPC cluster with 1000 cores, 2 TB aggregate memory, and MPI for communication. I am primarily looking for scalable, high-performance graph libraries that could be used in either single or multi-threaded scenarios, but parallel analysis libraries based on MPI or a similar protocol for communication and/or distributed memory are also of interest for high-end problems. Target programming languages include C++, C, Java, and Python. My research to-date has come up with the following possible solutions for these languages: C++ -- The most viable solutions appear to be the Boost Graph Library and Parallel Boost Graph Library. I have looked briefly at MTGL, but it is currently slanted more toward massively multithreaded hardware architectures like the Cray XMT. C - igraph and SNAP (Small-world Network Analysis and Partitioning); latter uses OpenMP for parallelism on SMP systems. Java - I have found no parallel libraries here yet, but JGraphT and perhaps JUNG are leading contenders in the non-parallel space. Python - igraph and NetworkX look like the most solid options, though neither is parallel. There used to be Python bindings for BGL, but these are now unsupported; last release in 2005 looks stale now. Other topics here on SO that I've looked at have discussed graph libraries in C++, Java, Python, and other languages. However, none of these topics focused significantly on scalability. Does anyone have recommendations they can offer based on experience with any of the above or other library packages when applied to large graph analysis problems? Performance, scalability, and code stability/maturity are my primary concerns. Most of the specialized algorithms will be developed by my team with the exception of any graph-oriented parallel communication or distributed memory frameworks (where the graph state is distributed across a cluster).

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• Excel Graph: How can I turn data below in to a 'time based' graph

  - by Mike

  In my spreadsheet I am collecting time periods when certain values have been changed. The user is restricted to 4 time periods. I would like to show the data based on thos time periods. I've included a mock up' of the data and the type of graph I would like to create. I've tried to create it for the last hour but am obviously missing something so thought I'd ask around. http://i48.tinypic.com/55lezr.jpg Many thanks for any help Mike P.S How do I make this image appear in the message and not as a link?

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• Problem: Munin Graph

  - by Pablo

  I've been trying to install Munin for 15 days, I looked for information, analized logs, I even deleted and reinstalled Munin using YUM. I'm hosted at Media Temple on a VPS with CentOS. The problem is still there and It's driving me nuts. Graphics are shown as following: http://imageshack.us/photo/my-images/833/capturadepantalla201106u.png/ This is the configuration of my munin.conf file dbdir /var/lib/munin htmldir /var/www/munin logdir /var/log/munin rundir /var/run/munin [localhost] address **.**.***.*** #IP VPS This is the configuration of my munin-node.conf file log_level 4 log_file /var/log/munin/munin-node.log port 4949 pid_file /var/run/munin/munin-node.pid background 1 setseid 1 # Which port to bind to; host * user root group root setsid yes # Regexps for files to ignore ignore_file ~$ ignore_file \.bak$ ignore_file %$ ignore_file \.dpkg-(tmp|new|old|dist)$ ignore_file \.rpm(save|new)$ allow ^127\.0\.0\.1$ Thanks so much, I appreciate all the answers UPDATE munin-graph.log Jun 22 16:30:02 - Starting munin-graph Jun 22 16:30:02 - Processing domain: localhost Jun 22 16:30:02 - Graphed service : open_inodes (0.14 sec * 4) Jun 22 16:30:02 - Graphed service : sendmail_mailtraffic (0.10 sec * 4) Jun 22 16:30:02 - Graphed service : apache_processes (0.12 sec * 4) Jun 22 16:30:02 - Graphed service : entropy (0.10 sec * 4) Jun 22 16:30:02 - Graphed service : sendmail_mailstats (0.14 sec * 4) Jun 22 16:30:02 - Graphed service : processes (0.14 sec * 4) Jun 22 16:30:03 - Graphed service : apache_accesses (0.27 sec * 4) Jun 22 16:30:03 - Graphed service : apache_volume (0.15 sec * 4) Jun 22 16:30:03 - Graphed service : df (0.21 sec * 4) Jun 22 16:30:03 - Graphed service : netstat (0.19 sec * 4) Jun 22 16:30:03 - Graphed service : interrupts (0.14 sec * 4) Jun 22 16:30:03 - Graphed service : swap (0.14 sec * 4) Jun 22 16:30:04 - Graphed service : load (0.11 sec * 4) Jun 22 16:30:04 - Graphed service : sendmail_mailqueue (0.13 sec * 4) Jun 22 16:30:04 - Graphed service : cpu (0.21 sec * 4) Jun 22 16:30:04 - Graphed service : df_inode (0.16 sec * 4) Jun 22 16:30:04 - Graphed service : open_files (0.16 sec * 4) Jun 22 16:30:04 - Graphed service : forks (0.13 sec * 4) Jun 22 16:30:05 - Graphed service : memory (0.26 sec * 4) Jun 22 16:30:05 - Graphed service : nfs_client (0.36 sec * 4) Jun 22 16:30:05 - Graphed service : vmstat (0.10 sec * 4) Jun 22 16:30:05 - Processed node: localhost (3.45 sec) Jun 22 16:30:05 - Processed domain: localhost (3.45 sec) Jun 22 16:30:05 - Munin-graph finished (3.46 sec)

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• Improving the running time of Breadth First Search and Adjacency List creation

  - by user45957

  We are given an array of integers where all elements are between 0-9. have to start from the 1st position and reach end in minimum no of moves such that we can from an index i move 1 position back and forward i.e i-1 and i+1 and jump to any index having the same value as index i. Time Limit : 1 second Max input size : 100000 I have tried to solve this problem use a single source shortest path approach using Breadth First Search and though BFS itself is O(V+E) and runs in time the adjacency list creation takes O(n2) time and therefore overall complexity becomes O(n2). is there any way i can decrease the time complexity of adjacency list creation? or is there a better and more efficient way of solving the problem? int main(){ vector<int> v; string str; vector<int> sets[10]; cin>>str; int in; for(int i=0;i<str.length();i++){ in=str[i]-'0'; v.push_back(in); sets[in].push_back(i); } int n=v.size(); if(n==1){ cout<<"0\n"; return 0; } if(v[0]==v[n-1]){ cout<<"1\n"; return 0; } vector<int> adj[100001]; for(int i=0;i<10;i++){ for(int j=0;j<sets[i].size();j++){ if(sets[i][j]>0) adj[sets[i][j]].push_back(sets[i][j]-1); if(sets[i][j]<n-1) adj[sets[i][j]].push_back(sets[i][j]+1); for(int k=j+1;k<sets[i].size();k++){ if(abs(sets[i][j]-sets[i][k])!=1){ adj[sets[i][j]].push_back(sets[i][k]); adj[sets[i][k]].push_back(sets[i][j]); } } } } queue<int> q; q.push(0); int dist[100001]; bool visited[100001]={false}; dist[0]=0; visited[0]=true; int c=0; while(!q.empty()){ int dq=q.front(); q.pop(); c++; for(int i=0;i<adj[dq].size();i++){ if(visited[adj[dq][i]]==false){ dist[adj[dq][i]]=dist[dq]+1; visited[adj[dq][i]]=true; q.push(adj[dq][i]); } } } cout<<dist[n-1]<<"\n"; return 0; }

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• Cross-platform DirectShow alternatives for real life graph

  - by Ole Jak

  Today I have such graph. I run it on windows I need some easy crossplatform DirectShow like alternative where to reconstruct such graph will not be a hard task. Where can I get such alternative? *(and If you can presenta way to reconstruct such graph in It It would be grate!) BTW: By crossplatform I mean Linux Mac and Windows compatible, By using SampleGrabber I ment I need to be able to get data from that step of graph from my programm and I use VirtualCamera from here soundmorning.com/download.php

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• How can I find the shortest path between two subgraphs of a larger graph?

  - by Pops

  I'm working with a weighted, undirected multigraph (loops not permitted; most node connections have multiplicity 1; a few node connections have multiplicity 2). I need to find the shortest path between two subgraphs of this graph that do not overlap with each other. There are no other restrictions on which nodes should be used as start/end points. Edges can be selectively removed from the graph at certain times (as explained in my previous question) so it's possible that for two given subgraphs, there might not be any way to connect them. I'm pretty sure I've heard of an algorithm for this before, but I can't remember what it's called, and my Google searches for strings like "shortest path between subgraphs" haven't helped. Can someone suggest a more efficient way to do this than comparing shortest paths between all nodes in one subgraph with all nodes in the other subgraph? Or at least tell me the name of the algorithm so I can look it up myself? For example, if I have the graph below, the nodes circled in red might be one subgraph and the nodes circled in blue might be another. The edges would all have positive integer weights, although they're not shown in the image. I'd want to find whatever path has the shortest total cost as long as it starts at a red node and ends at a blue node. I believe this means the specific node positions and edge weights cannot be ignored. (This is just an example graph I grabbed off Wikimedia and drew on, not my actual problem.)

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• Given an XML which contains a representation of a graph, how to apply it DFS algorithm? [on hold]

  - by winston smith

  Given the followin XML which is a directed graph: <?xml version="1.0" encoding="iso-8859-1" ?> <!DOCTYPE graph PUBLIC "-//FC//DTD red//EN" "../dtd/graph.dtd"> <graph direct="1"> <vertex label="V0"/> <vertex label="V1"/> <vertex label="V2"/> <vertex label="V3"/> <vertex label="V4"/> <vertex label="V5"/> <edge source="V0" target="V1" weight="1"/> <edge source="V0" target="V4" weight="1"/> <edge source="V5" target="V2" weight="1"/> <edge source="V5" target="V4" weight="1"/> <edge source="V1" target="V2" weight="1"/> <edge source="V1" target="V3" weight="1"/> <edge source="V1" target="V4" weight="1"/> <edge source="V2" target="V3" weight="1"/> </graph> With this classes i parsed the graph and give it an adjacency list representation: import java.io.IOException; import java.util.HashSet; import java.util.LinkedList; import java.util.Collection; import java.util.Iterator; import java.util.logging.Level; import java.util.logging.Logger; import practica3.util.Disc; public class ParsingXML { public static void main(String[] args) { try { // TODO code application logic here Collection<Vertex> sources = new HashSet<Vertex>(); LinkedList<String> lines = Disc.readFile("xml/directed.xml"); for (String lin : lines) { int i = Disc.find(lin, "source=\""); String data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } Vertex v = new Vertex(); v.setName(data); v.setAdy(new HashSet<Vertex>()); sources.add(v); } } Iterator it = sources.iterator(); while (it.hasNext()) { Vertex ver = (Vertex) it.next(); Collection<Vertex> adyacencias = ver.getAdy(); LinkedList<String> ls = Disc.readFile("xml/graphs.xml"); for (String lin : ls) { int i = Disc.find(lin, "target=\""); String data = ""; if (lin.contains("source=\""+ver.getName())) { Vertex v = new Vertex(); if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setName(data); } i = Disc.find(lin, "weight=\""); data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setWeight(Integer.parseInt(data)); } if (v.getName() != null) { adyacencias.add(v); } } } } for (Vertex vert : sources) { System.out.println(vert); System.out.println("adyacencias: " + vert.getAdy()); } } catch (IOException ex) { Logger.getLogger(ParsingXML.class.getName()).log(Level.SEVERE, null, ex); } } } This is another class: import java.util.Collection; import java.util.Objects; public class Vertex { private String name; private int weight; private Collection ady; public Collection getAdy() { return ady; } public void setAdy(Collection adyacencias) { this.ady = adyacencias; } public String getName() { return name; } public void setName(String nombre) { this.name = nombre; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int hashCode() { int hash = 7; hash = 43 * hash + Objects.hashCode(this.name); hash = 43 * hash + this.weight; return hash; } @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final Vertex other = (Vertex) obj; if (!Objects.equals(this.name, other.name)) { return false; } if (this.weight != other.weight) { return false; } return true; } @Override public String toString() { return "Vertice{" + "name=" + name + ", weight=" + weight + '}'; } } And finally: /** * * @author user */ /* -*-jde-*- */ /* <Disc.java> Contains the main argument*/ import java.io.*; import java.util.LinkedList; /** * Lectura y escritura de archivos en listas de cadenas * Ideal para el uso de las clases para gráficas. * * @author Peralta Santa Anna Victor Miguel * @since Julio 2011 */ public class Disc { /** * Metodo para lectura de un archivo * * @param fileName archivo que se va a leer * @return El archivo en representacion de lista de cadenas */ public static LinkedList<String> readFile(String fileName) throws IOException { BufferedReader file = new BufferedReader(new FileReader(fileName)); LinkedList<String> textlist = new LinkedList<String>(); while (file.ready()) { textlist.add(file.readLine().trim()); } file.close(); /* for(String linea:textlist){ if(linea.contains("source")){ //String generado = linea.replaceAll("<\\w+\\s+\"", ""); //System.out.println(generado); } }*/ return textlist; }//readFile public static int find(String linea,String palabra){ int i,j; boolean found = false; for(i=0,j=0;i<linea.length();i++){ if(linea.charAt(i)==palabra.charAt(j)){ j++; if(j==palabra.length()){ found = true; return i; } }else{ continue; } } if(!found){ i= -1; } return i; } /** * Metodo para la escritura de un archivo * * @param fileName archivo que se va a escribir * @param tofile la lista de cadenas que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String fileName, LinkedList<String> tofile, boolean append) throws IOException { FileWriter file = new FileWriter(fileName, append); for (int i = 0; i < tofile.size(); i++) { file.write(tofile.get(i) + "\n"); } file.close(); }//writeFile /** * Metodo para escritura de un archivo * @param msg archivo que se va a escribir * @param tofile la cadena que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String msg, String tofile, boolean append) throws IOException { FileWriter file = new FileWriter(msg, append); file.write(tofile); file.close(); }//writeFile }// I'm stuck on what can be the best way to given an adjacency list representation of the graph how to apply it Depth-first search algorithm. Any idea of how to aproach to complete the task?

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• What is the relaxation condition in graph theory

  - by windopal

  Hi, I'm trying to understand the main concepts of graph theory and the algorithms within it. Most algorithms seem to contain a "Relaxation Condition" I'm unsure about what this is. Could some one explain it to me please. An example of this is dijkstras algorithm, here is the pseudo-code. 1 function Dijkstra(Graph, source): 2 for each vertex v in Graph: // Initializations 3 dist[v] := infinity // Unknown distance function from source to v 4 previous[v] := undefined // Previous node in optimal path from source 5 dist[source] := 0 // Distance from source to source 6 Q := the set of all nodes in Graph // All nodes in the graph are unoptimized - thus are in Q 7 while Q is not empty: // The main loop 8 u := vertex in Q with smallest dist[] 9 if dist[u] = infinity: 10 break // all remaining vertices are inaccessible from source 11 remove u from Q 12 for each neighbor v of u: // where v has not yet been removed from Q. 13 alt := dist[u] + dist_between(u, v) 14 if alt < dist[v]: // Relax (u,v,a) 15 dist[v] := alt 16 previous[v] := u 17 return dist[] Thanks

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• Perl graph garbage collection usage

  - by Kevin

  Hi, I have built a tiny application in Perl that displays a graph over time. It graphs garbage collection usage over time. I use gnuplot to display the actual graph. This works fine if the time period is short, like a few hours. However, as the time increases (say a few days), the graph becomes difficult to read as the information gets crammed. Note that there is a tool called gcviewer which performs a similar function, it works by allowing you to choose the percentage of the graph. http://www.tagtraum.com/gcviewer.html Ideally I would like to take this further by adding the ability to "move" within the graph. I am not a developer but am good at scripting, so if there is some module in Perl which would provide this functionality it would be excellent! However, if it cannot be done in Perl, I am not averse to learning a new technology. Inputs are highly appreciated. Thanks!

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• Silverlight Line Graph with Gradient

  - by gav

  I have a series of points which I will turn into a line on a graph. What I want is to give the area under the graph a gradient fill. It would look somewhat similar to a Bloomberg graph like this; My question really has three parts; First, how should I fill only the area under the graph? Second, how do I fill that with a gradient? Finally, if I have multiple lines on the same graph any area under more than one line should have a greyscale gradient fill, how would you set this up? My biggest problem is deciding on the data structures to use, I could use many multiple sided shapes (One for each line/ data series) and then tell the brush to draw; Transparent if it's not in any shape The colour of one series if it's in one shape (Alpha relative to height to give grad) Black if it's in multiple shapes (Alpha relative to height to give grad) Then I'd draw the shapes' boundaries in white afterwards. Thanks, Gav

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• Graph Databases' Implementation

  - by user1478153

  I am having trouble visualizing a Graph Database. Visualizing an RDBMS is really very simple and I was able to understand from the first tutorial itself when I started learning it some 4-5 years ago. But I am not able to understand Graph Databases. I am also unable to get any good links on this topic, hence posting this question here. Specifically, I am looking for the following: Some really simple book/link on Graph Dbs Atleast some knowledge on the implementation details of a Graph DB (I hope all Graph DBs would be having atleast a few basic things in common). Thanks a lot in advance guys,

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• Eliminating cyclic flows from a graph

  - by Jon Harrop

  I have a directed graph with flow volumes along edges and I would like to simplify it by removing all cyclic flows. This can be done by finding the minimum of the flow volumes along each edge in any given cycle and reducing the flows of every edge in the cycle by that minimum volume, deleting edges with zero flow. When all cyclic flows have been removed the graph will be acyclic. For example, if I have a graph with vertices A, B and C with flows of 1 from A?B, 2 from B?C and 3 from C?A then I can rewrite this with no flow from A?B, 1 from B?C and 2 from C?A. The number of edges in the graph has reduced from 3 to 2 and the resulting graph is acyclic. Which algorithm(s), if any, solve this problem?

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• Would a model like this translate well to a document or graph database?

  - by Eric

  I'm trying to understand what types of models that I have traditionally persisted relationally would translate well to some kind of NoSQL database. Suppose I have a model with the following relationships: Product 1-----0..N Order Customer 1-----0..N Order And suppose I need to frequently query things like All Orders, All Products, All Customers, All Orders for Given Customer, All Orders for Given Product. My feeling is that this kind of model would not denormalize cleanly - If I had Product and Customer documents with embedded Orders, both documents would have duplicate orders. So I think I'd need separate documents for all three entities. Does a characteristic like this typically indicate that a document database is not well suited for a given model? Generally speaking, would a document database perform as well as a relational database in this kind of situation? I know very little about graph databases, but I understand that a graph database handles relationships more performantly than a document database - would a graph database be suited for this kind of model?

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• Howto use FB Graph to post a message on a feed (wall)

  - by qualbeen

  I have created an app, and now i want to post a message on one of my friends wall with use of the new Graph API. Is this do-able? I am already using oAuth and the Graph-api to get a list of all my friends. The API at http://developers.facebook.com/docs/api tells me to cURL https://graph.facebook.com/[userid]/feed to read the feed, but it also tells me howto post a message: curl -F 'access_token=[...]' -F 'message=Hello, Arjun. I like this new API.' https://graph.facebook.com/arjun/feed Ofcourse this doesn't work! And I can't find out why.. Here are my PHP-code: require_once 'facebook.php'; // PHP-SDK downloaded from http://github.com/facebook/php-sdk $facebook = new Facebook(array(appId=>123, secret=>'secret')); $result = $facebook->api( '/me/feed/', array('access_token' => $this->access_token, 'message' => 'Playing around with FB Graph..') ); This code does not throws any error, and I know my access_token are correct (otherwise i could't run $facebook-api('/me?access_token='.$this-access_token); to get my userobject. Have anyone out there sucsessfully posted a message using Graph-api? Then i need your help! :-)

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• Big problem with Dijkstra algorithm in a linked list graph implementation

  - by Nazgulled

  Hi, I have my graph implemented with linked lists, for both vertices and edges and that is becoming an issue for the Dijkstra algorithm. As I said on a previous question, I'm converting this code that uses an adjacency matrix to work with my graph implementation. The problem is that when I find the minimum value I get an array index. This index would have match the vertex index if the graph vertexes were stored in an array instead. And the access to the vertex would be constant. I don't have time to change my graph implementation, but I do have an hash table, indexed by a unique number (but one that does not start at 0, it's like 100090000) which is the problem I'm having. Whenever I need, I use the modulo operator to get a number between 0 and the total number of vertices. This works fine for when I need an array index from the number, but when I need the number from the array index (to access the calculated minimum distance vertex in constant time), not so much. I tried to search for how to inverse the modulo operation, like, 100090000 mod 18000 = 10000 and, 10000 invmod 18000 = 100090000 but couldn't find a way to do it. My next alternative is to build some sort of reference array where, in the example above, arr[10000] = 100090000. That would fix the problem, but would require to loop the whole graph one more time. Do I have any better/easier solution with my current graph implementation?

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• Detecting Asymptotes in a Graph

  - by nasufara

  I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with asymptotes. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with asymptotes using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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