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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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  • Detecting Singularities 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 singularities. 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 singularities 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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  • Scientific Data processing(Graph comparison and interpretation)

    - by pinkynobrain
    Hi stackoverflow friends, I'm trying to write a program to automate one of my more boring and repetative work tasks. I have some programming experience but none with processing or interpreting large volumes of data so i am seeking your advice(both suggestions of techneques to try and also things to read to learn more about doing this stuff). I have a piece of equipment that monitors an experiment by taking repeated samples and displays the readings on its screen as a graph. The input of experiment can be altered and one of these changes should produce a change in a section of the graph which i currently identify by eye and is what im looking for in the experiment. I want to automate it so that a computer looks at a set of results and spots the experiment input that causes the change. I can already extract the results from the machine. Currently they results for a run are in the form of an integer array with the index being the sample number and the corresponding value being the measurement. The overall shape of the graph will be similar for each experiment run. The change im looking for will be roughly the same and will occur in approximatly the same place every time for the correct experiment input. Unfortunatly there are a few gotcha's that make this problem more difficult. There is some noise in the measuring process which mean there is some random variation in the measured values between different runs. Although the overall shape of the graph remains the same. The time the experiment takes varies slightly each run causing two effects. First, the a whole graph may be shifted slightly on the x axis relative to another runs graph. Second, individual features may appear slightly wider or narrower in different runs. In both these cases the variation isn't particularly large and you can assume that the only non random variation is caused by the correct input being found. Thank you for your time, Pinky

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  • Scientific Data processing (Graph comparison and interpretation)

    - by pinkynobrain
    Hi stackoverflow friends, I'm trying to write a program to automate one of my more boring and repetitive work tasks. I have some programming experience but none with processing or interpreting large volumes of data so I am seeking your advice (both suggestions of techniques to try and also things to read to learn more about doing this stuff). I have a piece of equipment that monitors an experiment by taking repeated samples and displays the readings on its screen as a graph. The input of experiment can be altered and one of these changes should produce a change in a section of the graph which I currently identify by eye and is what I'm looking for in the experiment. I want to automate it so that a computer looks at a set of results and spots the experiment input that causes the change. I can already extract the results from the machine. Currently they results for a run are in the form of an integer array with the index being the sample number and the corresponding value being the measurement. The overall shape of the graph will be similar for each experiment run. The change I'm looking for will be roughly the same and will occur in approximately the same place every time for the correct experiment input. Unfortunately there are a few gotchas that make this problem more difficult. There is some noise in the measuring process which mean there is some random variation in the measured values between different runs. Although the overall shape of the graph remains the same. The time the experiment takes varies slightly each run causing two effects. First, the a whole graph may be shifted slightly on the x axis relative to another run's graph. Second, individual features may appear slightly wider or narrower in different runs. In both these cases the variation isn't particularly large and you can assume that the only non random variation is caused by the correct input being found. Thank you for your time, Pinky

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  • What would you add to Code Complete 3rd Edition?

    - by Peter Turner
    It's been quite a few years since Code Complete was published. I really love the book, I keep it in the bathroom at the office and read a little out of it once or twice a day. I was just wondering for the sake of wonderment, what kinds of things need to be added to Code Complete 3e, and for the sake of reductionism, what kinds of things would be removed. Also, what languages would you use for code examples?

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  • Which technology is best suited to store and query a huge readonly graph?

    - by asmaier
    I have a huge directed graph: It consists of 1.6 million nodes and 30 million edges. I want the users to be able to find all the shortest connections (including incoming and outgoing edges) between two nodes of the graph (via a web interface). At the moment I have stored the graph in a PostgreSQL database. But that solution is not very efficient and elegant, I basically need to store all the edges of the graph twice (see my question PostgreSQL: How to optimize my database for storing and querying a huge graph). It was suggested to me to use a GraphDB like neo4j or AllegroGraph. However the free version of AllegroGraph is limited to 50 million nodes and also has a very high-level API (RDF), which seems too powerful and complex for my problem. Neo4j on the other hand has only a very low level API (and the python interface is not mature yet). Both of them seem to be more suited for problems, where nodes and edges are frequently added or removed to a graph. For a simple search on a graph, these GraphDBs seem to be too complex. One idea I had would be to "misuse" a search engine like Lucene for the job, since I'm basically only searching connections in a graph. Another idea would be, to have a server process, storing the whole graph (500MB to 1GB) in memory. The clients could then query the server process and could transverse the graph very quickly, since the graph is stored in memory. Is there an easy possibility to write such a server (preferably in Python) using some existing framework? Which technology would you use to store and query such a huge readonly graph?

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  • Add a wall post to a page or application wall as page or application with facebook graph API

    - by blauesocke
    Hi, I wan't to create a new wall post on a appliaction page or a "normal" page with the facebook graph API. Is there a way to "post as page"? With the old REST-API it worked like this: $facebook->api_client->stream_publish($message, NULL, $links, $targetPageId, $asPageId); So, if I passed equal IDs for $targetPageId and $asPageId I was able to post a "real" wall post not caused by my own facebook account. Thanks!

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  • How can I get node coordinates from a graph, using Perl?

    - by jonny
    Ok, I have a flowchart definition (basically, array of nodes and edges for each node). Now I want to calculate coordinates for every task in the flow, preferably hierarchycal style. I need something like Graph::Easy::Layout but I have no idea how to get nodes coordinates: I render nodes myself and I only want to retrieve box coordinates/size. Any suggestions? What I need is a CPAN module available even in Debian repository.

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  • How can I tag a user in a photo using the Facebook Graph API?

    - by fr6
    I tried: $args = array( 'access_token' => $access_token, 'id' => $uid ); $url = "https://graph.facebook.com/{$idPhoto}/tags"; $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_HEADER, false); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_POSTFIELDS, $args); curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2); $data = curl_exec($ch); It has returned me: {"error":{"type":"QueryParseException","message":"Unknown path components: \/tags"}} It does not seem possible because its not in the Facebook documentation: http://developers.facebook.com/docs/api#publishing Can someone confirm me that it's not possible to tag a user in a recently uploaded photo?

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  • Error with python-setuptools doing "sudo easy_install python-graph-core"

    - by Dan
    Using easy_install, part of the python-setuptools, I get the following error: $ sudo easy_install python-graph-core [sudo] password for dan: Searching for python-graph-core Reading http://pypi.python.org/simple/python-graph-core/ Reading http://code.google.com/p/python-graph/ Reading http://code.google.com/p/python-graph/downloads/list?can=1 Reading http://code.google.com/p/python-graph/downloads/list Best match: python-graph-core 1.7.0 Downloading http://python-graph.googlecode.com/files/python-graph-core-1.7.0.tar.gz Processing python-graph-core-1.7.0.tar.gz Running python-graph-core-1.7.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-GwpYiM/python-graph-core-1.7.0/egg-dist-tmp-1yqbyV setup.py:8: Warning: 'as' will become a reserved keyword in Python 2.6 Traceback (most recent call last): File "/usr/bin/easy_install", line 8, in <module> load_entry_point('setuptools==0.6c9', 'console_scripts', 'easy_install')() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1671, in main with_ei_usage(lambda: File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1659, in with_ei_usage return f() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1675, in <lambda> distclass=DistributionWithoutHelpCommands, **kw File "/usr/lib/python2.5/distutils/core.py", line 151, in setup dist.run_commands() File "/usr/lib/python2.5/distutils/dist.py", line 974, in run_commands self.run_command(cmd) File "/usr/lib/python2.5/distutils/dist.py", line 994, in run_command cmd_obj.run() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 211, in run self.easy_install(spec, not self.no_deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 446, in easy_install return self.install_item(spec, dist.location, tmpdir, deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 476, in install_item dists = self.install_eggs(spec, download, tmpdir) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 655, in install_eggs return self.build_and_install(setup_script, setup_base) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 930, in build_and_install self.run_setup(setup_script, setup_base, args) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 919, in run_setup run_setup(setup_script, args) File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 27, in run_setup lambda: execfile( File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 63, in run return func() File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 29, in <lambda> {'__file__':setup_script, '__name__':'__main__'} File "setup.py", line 8 except ImportError as ie: ^ SyntaxError: invalid syntax Any suggestions to what I may be doing wrong? Thanks, Dan

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  • Looking for app to work fluidly with CSV data in graph form

    - by Aszurom
    It often occurs to me that if I had a good tool for viewing CSV data in graphical format, and comparing two sets of numbers to each other, I could do a great deal of meaningful trend watching and data interpretation. For example, perfmon can output quite a lot of data about a server into a CSV file, but there's no good way to view it. A lot of scripts could/have been written that would populate CSV files. I could write these all day long. My problem is that I need a great viewer. I've seen quite a few things that will take a CSV file and after a lot of tweaking and user adjustment produce a static gif/png image. A static image doesn't do me a lot of good, because I have to look at it, then re-calibrate the parameters of the program, regenerate the image, repeat. That sucks. I could do this in Excel. Ideally, I would want a FLUID graph viewer. On the fly, I can adjust how much of my timeline I'm viewing. I could adjust the scaling so that one big spike doesn't make 99.9% of the data an unreadable line across the bottom of the X axis. Stuff like that. I should be able to say "show me CSV column 3 and column 5 as graphs. Show me the data scaled for 20 or 150 entries, and let me slide that window up and down the column of data. Auto scale to fit 95% of data within the Y axis and let crazy spikes go off the screen." Maybe I'm terribly spoiled by how you can drag, zoom, and slide data around on my iPad. I want to be able to view a spreadsheet of data with that fluidity and not have to guess at what sort of static snapshot I want to create from it. I don't want to have to make a study of how to tweak some data plotting program to let me import my file and do what I could just do in Excel. I want to scale, zoom, and transform my graph on the fly and then export a snapshot of it once I have it the way I want it. Is there anything out there that fills this need? I'll take linux, osx, win32 or even iOS suggestions.

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  • How to find whole graph coverage path in dynamic state-flow diagram?

    - by joseph
    Hello, As I've been researching algorithms for path finding in graph, I found interesting problem. Definition of situation: 1)State diagram can have p states, and s Boolean Fields, and z Int Fields 2)Every state can have q ingoing and r outgoing transitions, and h Int fields (h belongs to z - see above) 3)Every transition can have only 1 event, and only 1 action 4)every action can change n Boolean Fields, and x Int Fields 5)every event can have one trigger from combination of any count of Boolean Fields in diagram 6)Transition can be in OPEN/CLOSED form. If the transition is open/closed depends on trigger2 compounded from 0..c Boolean fields. 7) I KNOW algorithm for finding shortest paths from state A to state B. 8) I KNOW algorithm for finding path that covers all states and transitions of whole state diagram, if all transitions are OPEN. Now, what is the goal: I need to find shortest path that covers all states and transitions in dynamically changing state diagram described above. When an action changes some int field, the algorithm should go through all states that have changed int field. The algorithm should also be able to open and close transition (by going through transitions that open and close another transitions by action) in the way that the founded path will be shortest and covers all transitions and states. Any idea how to solve it? I will be really pleased for ANY idea. Thanks for answers.

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  • boost graph adjacency_list, retrieving a node's parents

    - by Juan
    I want to find in an adjacency graph from the bgl how give a Vertexdescriptor and get the set of nodes that are parents of this given node. i would like to do this in directed graph, it seems you could use a bidirectional graph but i want to be able to restrict it so that there are no cycles.

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  • is OAuth required in Facebook Graph API ?

    - by From.ME.to.YOU
    Hello i have a problem .. i want to get all the feeds from a facebook page using fb graph API without OAuth but i have a problem https://graph.facebook.com/[page ID]/feed i get the following response { "error": { "type": "OAuthAccessTokenException", "message": "An access token is required to request this resource." } } while i check another page it gets right response https://graph.facebook.com/[another page ID]/feed { "data": [ { ... why it's asking for an access token for a page ... and it doesn't do that for another page ?

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  • A two way minimum spanning tree of a directed graph

    - by mvid
    Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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  • Like posts over Facebook graph api

    - by Sima
    HI! I have little problem with facebook PHP SDK..I want to like a post, or something else via facebook PHP SDK..I am doing this code, I think it should be right, but  apparently it's not working..The given error code is, the PHP SDK dont know this kind of POST request(the generated link is definitely alright). What I have seen on Facebook Developers page is about the same..There is an example of Curl command, and I the PHP SDK is doing this requests over Curl (propably). $this->getFacebook()->api("/"+$id+"/likes", 'post'); This is what I am using in my code and it's not working(Facebook API Exception unsupported post request). Maybe, I have bad syntax in my code, but, for example, when I want to post a status to my Profile, it's working..Another cause which confused me, was when I tried to fetch these data over Graph api(on the documentation page is written, I should use address like graph.facebook.com/POST_ID/likes)... You can comment on or like a post by posting to https://graph.facebook.com/POST_ID/comments and https://graph.facebook.com/POST_ID/likes,respectively: curl -F 'access_token=...' \ https://graph.facebook.com/313449204401/likes <=this is from facebook documentation And all these requests or commands(liking ones, comments have I not yet tried) are putting me back a JSON array which contents any already existing likes, but my like is nowhere. Does anyone know what to do?How to like a post from PHP..There are other SKDs like FQL, but I haven't any knowlegde with it, so I like rather to use the standard PHP SDK(but if is there some possibility how to call for example FQL from PHP SDK, here I am:)) Please help..

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