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  • Prevent recursive CTE visiting nodes multiple times

    - by bacar
    Consider the following simple DAG: 1->2->3->4 And a table, #bar, describing this (I'm using SQL Server 2005): parent_id child_id 1 2 2 3 3 4 //... other edges, not connected to the subgraph above Now imagine that I have some other arbitrary criteria that select the first and last edges, i.e. 1-2 and 3-4. I want to use these to find the rest of my graph. I can write a recursive CTE as follows (I'm using terminology from MSDN): with foo(parent_id,child_id) as ( // anchor member that happens to select first and last edges: select parent_id,child_id from #bar where parent_id in (1,3) union all // recursive member: select #bar.* from #bar join foo on #bar.parent_id = foo.child_id ) select parent_id,child_id from foo However, this results in edge 3-4 being selected twice: parent_id child_id 1 2 3 4 2 3 3 4 // 2nd appearance! How can I prevent the query from recursing into subgraphs that have already been described? I could achieve this if, in my "recursive member" part of the query, I could reference all data that has been retrieved by the recursive CTE so far (and supply a predicate indicating in the recursive member excluding nodes already visited). However, I think I can access data that was returned by the last iteration of the recursive member only. This will not scale well when there is a lot of such repetition. Is there a way of preventing this unnecessary additional recursion? Note that I could use "select distinct" in the last line of my statement to achieve the desired results, but this seems to be applied after all the (repeated) recursion is done, so I don't think this is an ideal solution. Edit - hainstech suggests stopping recursion by adding a predicate to exclude recursing down paths that were explicitly in the starting set, i.e. recurse only where foo.child_id not in (1,3). That works for the case above only because it simple - all the repeated sections begin within the anchor set of nodes. It doesn't solve the general case where they may not be. e.g., consider adding edges 1-4 and 4-5 to the above set. Edge 4-5 will be captured twice, even with the suggested predicate. :(

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  • Problem on a Floyd-Warshall implementation using c++

    - by Henrique
    I've got a assignment for my college, already implemented Dijkstra and Bellman-Ford sucessfully, but i'm on trouble on this one. Everything looks fine, but it's not giving me the correct answer. Here's the code: void FloydWarshall() { //Also assume that n is the number of vertices and edgeCost(i,i) = 0 int path[500][500]; /* A 2-dimensional matrix. At each step in the algorithm, path[i][j] is the shortest path from i to j using intermediate vertices (1..k-1). Each path[i][j] is initialized to edgeCost(i,j) or infinity if there is no edge between i and j. */ for(int i = 0 ; i <= nvertices ; i++) for(int j = 0 ; j <= nvertices ; j++) path[i][j] = INFINITY; for(int j = 0 ; j < narestas ; j++) //narestas = number of edges { path[arestas[j]->v1][arestas[j]->v2] = arestas[j]->peso; //peso = weight of the edge (aresta = edge) path[arestas[j]->v2][arestas[j]->v1] = arestas[j]->peso; } for(int i = 0 ; i <= nvertices ; i++) //path(i, i) = 0 path[i][i] = 0; //test print, it's working fine //printf("\n\n\nResultado FloydWarshall:\n"); //for(int i = 1 ; i <= nvertices ; i++) // printf("distancia ao vertice %d: %d\n", i, path[1][i]); //heres the problem, it messes up, and even a edge who costs 4, and the minimum is 4, it prints 2. //for k = 1 to n for(int k = 1 ; k <= nvertices ; k++) //for i = 1 to n for(int i = 1 ; i <= nvertices ; i++) //for j := 1 to n for(int j = 1 ; j <= nvertices ; j++) if(path[i][j] > path[i][k] + path[k][j]) path[i][j] = path[i][k] + path[k][j]; printf("\n\n\nResultado FloydWarshall:\n"); for(int i = 1 ; i <= nvertices ; i++) printf("distancia ao vertice %d: %d\n", i, path[1][i]); } im using this graph example i've made: 6 7 1 2 4 1 5 1 2 3 1 2 5 2 5 6 3 6 4 6 3 4 2 means we have 6 vertices (1 to 6), and 7 edges (1,2) with weight 4... etc.. If anyone need more info, i'm up to giving it, just tired of looking at this code and not finding an error.

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  • Is there a way to make PHP's SplHeap recalculate? (aka: add up-heap to SplHeap?)

    - by md2k7
    I am using an SplHeap to hold graph nodes of a tree with directed edges that will be traversed from the leaves to the root. For this, I precalculate the "fan-in" of nodes and put them into the heap so that I can always retrieve the node with the smallest fan-in (0) from it. After visiting a node, I reduce the fan-in of its successor by 1. Then obviously, the heap needs to be recalculated because the successor is now in the wrong place there. I have tried recoverFromCorruption(), but it doesn't do anything and keeps the heap in the wrong order (node with larger fanIn stays in front of smaller fanIn). As a workaround, I'm now creating a new heap after each visit, amounting to a full O(N*log(N)) sort each time. It should be possible, however, to make up-heap operations on the changed heap entry until it's in the right position in O(log(N)). The API for SplHeap doesn't mention an up-heap (or deletion of an arbitrary element - it could then be re-added). Can I somehow derive a class from SplHeap to do this or do I have to create a pure PHP heap from scratch? EDIT: Code example: class VoteGraph { private $nodes = array(); private function calculateFanIn() { /* ... */ } // ... private function calculateWeights() { $this->calculateFanIn(); $fnodes = new GraphNodeHeap(); // heap by fan-in ascending (leaves are first) foreach($this->nodes as $n) { // omitted: filter loops $fnodes->insert($n); } // traversal from leaves to root while($fnodes->valid()) { $node = $fnodes->extract(); // fetch a leaf from the heap $successor = $this->nodes[$node->successor]; // omitted: actual job of traversal $successor->fanIn--; // will need to fix heap (sift up successor) because of this //$fnodes->recoverFromCorruption(); // doesn't work for what I want // workaround: rebuild $fnodes from scratch $fixedHeap = new GraphNodeHeap(); foreach($fnodes as $e) $fixedHeap->insert($e); $fnodes = $fixedHeap; } } } class GraphNodeHeap extends SplHeap { public function compare($a, $b) { if($a->fanIn === $b->fanIn) return 0; else return $a->fanIn < $b->fanIn ? 1 : -1; } }

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  • The illusion of Competence

    - by tony_lombardo
    Working as a contractor opened my eyes to the developer food chain.  Even though I had similar experiences earlier in my career, the challenges seemed much more vivid this time through.  I thought I’d share a couple of experiences with you, and the lessons that can be taken from them. Lesson 1: Beware of the “funnel” guy.  The funnel guy is the one who wants you to funnel all thoughts, ideas and code changes through him.  He may say it’s because he wants to avoid conflicts in source control, but the real reason is likely that he wants to hide your contributions.  Here’s an example.  When I finally got access to the code on one of my projects, I was told by the developer that I had to funnel all of my changes through him.  There were 4 of us coding on the project, but only 2 of us working on the UI.  The other 2 were working on a separate application, but part of the overall project.  So I figured, I’ll check it into SVN, he reviews and accepts then merges in.  Not even close.  I didn’t even have checkin rights to SVN, I had to email my changes to the developer so he could check those changes in.  Lesson 2: If you point out flaws in code to someone supposedly ‘higher’ than you in the developer chain, they’re going to get defensive.  My first task on this project was to review the code, familiarize myself with it.  So of course, that’s what I did.  And in familiarizing myself with it, I saw so many bad practices and code smells that I immediately started coming up with solutions to fix it.  Of course, when I reviewed these changes with the developer (guy who originally wrote the code), he smiled and nodded and said, we can’t make those changes now, it’s too destabilizing.  I recommended we create a new branch and start working on refactoring, but branching was a new concept for this guy and he was worried we would somehow break SVN. How about some concrete examples? I started out by recommending we remove NUnit dependency and tests from the application project, and create a separate Unit testing project.  This was met with a little bit of resistance because - “How do I access the private methods?”  As it turned out there weren’t really any private methods that weren’t exposed by public methods, so I quickly calmed this fear. Win 1 Loss 0 Next, I recommended that all of the File IO access be wrapped in Using clauses, or at least properly wrapped in try catch finally.  This recommendation was accepted.. but never implemented. Win 2  Loss 1 Next recommendation was to refactor the command pattern implementation.  The command pattern was implemented, but it wasn’t really necessary for the application.  More over, the fact that we had 100 different command classes, each with it’s own specific command parameters class, made maintenance a huge hassle.  The same code repeated over and over and over.  This recommendation was declined, the code was too fragile and this change would destabilize it.  I couldn’t disagree, though it was the commands themselves in many cases that were fragile. Win 2 Loss 2 Next recommendation was to aid performance (and responsiveness) of the application by using asynchronous service calls.  This on was accepted. Win 2 Loss 3 If you’re paying any attention, you’re wondering why the async service calls was scored as a loss.. Let me explain.  The service call was made using the async pattern.  Followed by a thread.sleep  <facepalm>. Now it’s easy to be harsh on this kind of code, especially if you’re an experienced developer.  But I understood how most of this happened.  One junior guy, working as hard as he can to build his first real world application, with little or no guidance from anyone else.  He had his pattern book and theory of programming to help him, but no real world experience.  He didn’t know how difficult it would be to trace the crashes to the coding issues above, but he will one day.  The part that amazed me was the management position that “this guy should be a team lead, because he’s worked so hard”.  I’m all for rewarding hard work, but when you reward someone by promoting them past the point of their competence, you’re setting yourself and them up for failure.  And that’s lesson 3.  Just because you’ve got a hard worker, doesn’t mean he should be leading a development project.  If you’re a junior guy busting your ass, keep at it.  I encourage you to try new things, but most importantly to learn from your mistakes.  And correct your mistakes.  And if someone else looks at your code and shows you a laundry list of things that should be done differently, don’t take it personally – they’re really trying to help you.  And if you’re a senior guy, working with a junior guy, it’s your duty to point out the flaws in the code.  Even if it does make you the bad guy.  And while I’ve used “guy” above, I mean both men and women.  And in some cases mutant dinosaurs. 

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  • JAVA BubbleSort Output Plotting

    - by John Smith
    I'm not sure how to plot the output I get with my run time results for BubbleSort. Here's the thing: I've written a working BubbleSort algorithm that does exactly as it should. But I wish to plot the output, to show the following: Best Case, Worst Case, Average Case ... How would I go about plotting it on a graph? Here is the code: public class BubbleSort { static double bestTime = 10000000, worstTime = 0; public static void main(String[] args) { int BubArray[] = new int[]{13981, 6793, 2662, 10986, 733, ... #1000 integers}; System.out.println("Unsorted List Before Bubble Sort"); for(int a = 0; a < BubArray.length; a++){ System.out.print(BubArray[a] + " "); } System.out.println("\n Bubble Sort Execution ..."); for(int i=0; i<10000;i++) { bubbleSortTimeTaken(BubArray, i); } int itrs = bubbleSort(BubArray); System.out.println(""); System.out.println("Array After Bubble Sort"); System.out.println("Moves Taken for Sort : " + itrs + " Moves."); System.out.println("BestTime: " + bestTime + " WorstTime: " + worstTime); System.out.print("Sorted Array: \n"); for(int a = 0; a < BubArray.length; a++){ System.out.print(BubArray[a] + " "); } } private static int bubbleSort(int[] BubArray) { int z = BubArray.length; int temp = 0; int itrs = 0; for(int a = 0; a < z; a++){ for(int x=1; x < (z-a); x++){ if(BubArray[x-1] > BubArray[x]){ temp = BubArray[x-1]; BubArray[x-1] = BubArray[x]; BubArray[x] = temp; } itrs++; } } return itrs; } public static void bubbleSortTimeTaken(int[] BubArray, int n) { long startTime = System.nanoTime(); bubbleSort(BubArray); double timeTaken = (System.nanoTime() - startTime)/1000000d; if (timeTaken > 0) { worstTime = timeTaken; } else if (timeTaken < bestTime) { bestTime = timeTaken; } System.out.println(n + "," + timeTaken); } } The output are as the following ( execution number, time (nano/10^6): Unsorted List Before Bubble Sort 13981 6793 2662 .... #1000 integers Bubble Sort Execution ... 0, 18.319891 1, 4.728978 2, 3.670697 3, 3.648922 4, 4.161576 5, 3.824369 .... 9995, 4.331423 9996, 3.692473 9997, 3.709893 9998, 6.16055 9999, 4.32209 Array After Bubble Sort Moves Taken for Sort : 541320 Moves. BestTime: 1.0E7 WorstTime: 4.32209 Sorted Array: 10 11 17 24 57 60 83 128 141 145 ... #1000 integers I am looking for graphs to represent Average, Best and Worst case based on the output but my current graphs don't look correct. Any help would be appreciated, thanks.

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  • python matrices - list index out of range

    - by user1888493
    I am writing a function, that takes a matrix as input, such as the one below. Then the it returns the matrix' inverse, where all the 1s are changed to 0s and all the 0s changed to 1s, while keeping the diagonal from top left to bottom right 0s. An example input: g1 = [[0, 1, 1, 0], [1, 0, 0, 1], [1, 0, 0, 1], [0, 1, 1, 0]] the function should output this: g1 = [[0, 0, 0, 1], [0, 0, 1, 0], [0, 1, 0, 0], [1, 0, 0, 0]] When I run the program, it raises a list index out of range error. I'm sure this happens, because the loops I have set up are trying to access values that do not exist. But how do I allow an input of unknown row and column size? I only know how to do this with a single list, but a list of lists? Following you see the transforming function, but not the test function that calls it: def inverse_graph(graph): # take in graph # change all zeros to ones and ones to zeros r, c = 0, 0 # row, column equal zero while (graph[r][c] == 0 or graph[r][c] == 1): # while the current row has a value. while (graph[r][c] == 0 or graph[r][c] == 1): # while the current column has a value if (graph[r][c] == 0): graph[r][c] = 1 elif (graph[r][c] == 1): graph[r][c] = 0 c+=1 c=0 r+=1 c=0 r=0 # sets diagonal to zeros while (g1[r][c] == 0 or g1[r][c] == 1): g1[r][c]=0 c+=1 r+=1 return graph

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  • Artichow PlotGroup: Legends not showing

    - by Hameed
    I am working on a little project on OpenCATS, developing some charts. In one of the charts, I need to add multiple plots to a PlotGroup and add Legends as well. I have written a small function that creates the chart, however I have difficulty displaying the legends when I add them to a PlotGroup object. Here is the code: public function draw($format = false) { /* Make sure we have GD support. */ if (!function_exists('imagecreatefromjpeg')) { die(); } if ($format === false) { $format = IMG_PNG; } $group = new PlotGroup(); $graph = new Graph($this->width, $this->height, NULL, 0, $this->width-135); $graph->setFormat($format); $graph->setBackgroundColor(new Color(0xF4, 0xF4, 0xF4)); $graph->shadow->setSize(3); $graph->title->set($this->title); $graph->title->setFont(new Tuffy(10)); $graph->title->setColor(new Color(0x00, 0x00, 0x8B)); $graph->border->setColor(new Color(187, 187, 187, 15)); $group->axis->bottom->setLabelText($this->xLabels); $group->axis->bottom->label->setFont(new Tuffy(8)); $group->setPadding(25, 145, 10, 22); $plotcount = 0; $plot = array(); foreach ($this->xValues as $xVal) { $plotcount++; $plot[$plotcount-1] = new LinePlot($xVal, LinePlot::LINE); $plot[$plotcount-1]->setPadding(25, 145, 10, 22); if ($plotcount % 5 ==0 ) $plot[$plotcount-1]->setColor(new Blue); else if ($plotcount % 4 ==0 ) $plot[$plotcount-1]->setColor(new DarkGreen); else if ($plotcount % 3 ==0 ) $plot[$plotcount-1]->setColor(new Red); else if ($plotcount % 2 ==0 ) $plot[$plotcount-1]->setColor(new Orange); $plot[$plotcount-1]->setThickness(2); $plot[$plotcount-1]->legend->add($plot[$plotcount-1], $this->legends[$plotcount-1]); $plot[$plotcount-1]->legend->setTextFont(new Tuffy(8)); $plot[$plotcount-1]->legend->setPadding(3, 3, 3, 3, 3); $plot[$plotcount-1]->legend->setPosition(1, 0.825); $plot[$plotcount-1]->legend->setBackgroundColor(new Color(0xFF, 0xFF, 0xFF)); $plot[$plotcount-1]->legend->border->setColor(new Color(0xD0, 0xD0, 0xD0)); $plot[$plotcount-1]->legend->shadow->setSize(0); $group->add($plot[$plotcount-1]); } $graph->add($group); $graph->draw(); } } If I draw only one LinePlot it works: So for instance if I change $graph->add($group); to $graph->add($plot[0]); then only one of the lines will show up with the legend next to it.

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  • Oracle Database 12c Spatial: Vector Performance Acceleration

    - by Okcan Yasin Saygili-Oracle
    Most business information has a location component, such as customer addresses, sales territories and physical assets. Businesses can take advantage of their geographic information by incorporating location analysis and intelligence into their information systems. This allows organizations to make better decisions, respond to customers more effectively, and reduce operational costs – increasing ROI and creating competitive advantage. Oracle Database, the industry’s most advanced database,  includes native location capabilities, fully integrated in the kernel, for fast, scalable, reliable and secure spatial and massive graph applications. It is a foundation for deploying enterprise-wide spatial information systems and locationenabled business applications. Developers can extend existing Oracle-based tools and applications, since they can easily incorporate location information directly in their applications, workflows, and services. Spatial Features The geospatial data features of Oracle Spatial and Graph option support complex geographic information systems (GIS) applications, enterprise applications and location services applications. Oracle Spatial and Graph option extends the spatial query and analysis features included in every edition of Oracle Database with the Oracle Locator feature, and provides a robust foundation for applications that require advanced spatial analysis and processing in the Oracle Database. It supports all major spatial data types and models, addressing challenging business-critical requirements from various industries, including transportation, utilities, energy, public sector, defense and commercial location intelligence. Network Data Model Graph Features The Network Data Model graph explicitly stores and maintains a persistent data model withnetwork connectivity and provides network analysis capability such as shortest path, nearest neighbors, within cost and reachability. It loads partitioned networks into memory on demand, overcomingthe limitations of in-memory analysis. Partitioning massive networks into manageable sub-networkssimplifies the network analysis. RDF Semantic Graph Features RDF Semantic Graph has native support for World Wide Web Consortium standards. It has open, scalable, and secure features for storing RDF/OWL ontologies anddata; native inference with OWL 2, SKOS and user-defined rules; and querying RDF/OWL data withSPARQL 1.1, Java APIs, and SPARQLgraph patterns in SQL. Video: Oracle Spatial and Graph Overview Oracle spatial is embeded on oracle database product. So ,we can use oracle installer (OUI).The Oracle Universal Installer (OUI) is used to install Oracle Database software. OUI is a graphical user interface utility that enables you to view the Oracle software that is installed on your machine, install new Oracle Database software, and delete Oracle software that you no longer need to use. Online Help is available to guide you through the installation process. One of the installation options is to create a database. If you select database creation, OUI automatically starts Oracle Database Configuration Assistant (DBCA) to guide you through the process of creating and configuring a database. If you do not create a database during installation, you must invoke DBCA after you have installed the software to create a database. You can also use DBCA to create additional databases. For installing Oracle Database 12c you may check the Installing Oracle Database Software and Creating a Database tutorial under the Oracle Database 12c 2-Day DBA Series.You can always check if spatial is available in your database using  "select comp_id, version, status, comp_name from dba_registry where comp_id='SDO';"   One of the most notable improvements with Oracle Spatial and Graph 12c can be seen in performance increases in vector data operations. Enabling the Spatial Vector Acceleration feature (available with the Spatial option) dramatically improves the performance of commonly used vector data operations, such as sdo_distance, sdo_aggr_union, and sdo_inside. With 12c, these operations also run more efficiently in parallel than in prior versions through the use of metadata caching. For organizations that have been facing processing limitations, these enhancements enable developers to make a small set of configuration changes and quickly realize significant performance improvements. Results include improved index performance, enhanced geometry engine performance, optimized secondary filter optimizations for Spatial operators, and improved CPU and memory utilization for many advanced vector functions. Vector performance acceleration is especially beneficial when using Oracle Exadata Database Machine and other large-scale systems. Oracle Spatial and Graph vector performance acceleration builds on general improvements available to all SDO_GEOMETRY operations in these areas: Caching of index metadata, Concurrent update mechanisms, and Optimized spatial predicate selectivity and cost functions. These optimizations enable more efficient use of: CPU, Memory, and Partitioning Resulting in substantial query performance improvements.UsageTo accelerate the performance of spatial operators, it is recommended that you set the SPATIAL_VECTOR_ACCELERATION database system parameter to the value TRUE. (This parameter is authorized for use only by licensed Oracle Spatial users, and its default value is FALSE.) You can set this parameter for the whole system or for a single session. To set the value for the whole system, do either of the following:Enter the following statement from a suitably privileged account:   ALTER SYSTEM SET SPATIAL_VECTOR_ACCELERATION = TRUE;Add the following to the database initialization file (xxxinit.ora):   SPATIAL_VECTOR_ACCELERATION = TRUE;To set the value for the current session, enter the following statement from a suitably privileged account:   ALTER SESSION SET SPATIAL_VECTOR_ACCELERATION = TRUE; Checkout the complete list of new features on Oracle.com @ http://www.oracle.com/technetwork/database/options/spatialandgraph/overview/index.html Spatial and Graph Data Sheet (PDF) Spatial and Graph White Paper (PDF)

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  • What is a good practice for 2D scene graph partitioning for culling?

    - by DevilWithin
    I need to know an efficient way to cull the scene graph objects, to render exclusively the ones in the view, and as fast as possible. I am thinking of doing it the following way, having in each object a local boundingbox which holds the object bounds, and a global boundingbox which holds the bounds of the object and all children. When a camera is moved, the render list is updated by traversing the global boundingboxes. When only the object is being moved, it tries to enlarge or shrink the ancestors global boundingboxes, and in the end updating or not the renderlist. What do you think of this approach? Do you think it will provide a fast and efficient culling? Also, because the render list is a contiguous list, it could accelerate the rendering, right? Any further tips for a 2D scene graphs are highly appreciated!

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  • Prim's MST algorithm implementation with Java

    - by user1290164
    I'm trying to write a program that'll find the MST of a given undirected weighted graph with Kruskal's and Prim's algorithms. I've successfully implemented Kruskal's algorithm in the program, but I'm having trouble with Prim's. To be more precise, I can't figure out how to actually build the Prim function so that it'll iterate through all the vertices in the graph. I'm getting some IndexOutOfBoundsException errors during program execution. I'm not sure how much information is needed for others to get the idea of what I have done so far, but hopefully there won't be too much useless information. This is what I have so far: I have a Graph, Edge and a Vertex class. Vertex class mostly just an information storage that contains the name (number) of the vertex. Edge class can create a new Edge that has gets parameters (Vertex start, Vertex end, int edgeWeight). The class has methods to return the usual info like start vertex, end vertex and the weight. Graph class reads data from a text file and adds new Edges to an ArrayList. The text file also tells us how many vertecis the graph has, and that gets stored too. In the Graph class, I have a Prim() -method that's supposed to calculate the MST: public ArrayList<Edge> Prim(Graph G) { ArrayList<Edge> edges = G.graph; // Copies the ArrayList with all edges in it. ArrayList<Edge> MST = new ArrayList<Edge>(); Random rnd = new Random(); Vertex startingVertex = edges.get(rnd.nextInt(G.returnVertexCount())).returnStartingVertex(); // This is just to randomize the starting vertex. // This is supposed to be the main loop to find the MST, but this is probably horribly wrong.. while (MST.size() < returnVertexCount()) { Edge e = findClosestNeighbour(startingVertex); MST.add(e); visited.add(e.returnStartingVertex()); visited.add(e.returnEndingVertex()); edges.remove(e); } return MST; } The method findClosesNeighbour() looks like this: public Edge findClosestNeighbour(Vertex v) { ArrayList<Edge> neighbours = new ArrayList<Edge>(); ArrayList<Edge> edges = graph; for (int i = 0; i < edges.size() -1; ++i) { if (edges.get(i).endPoint() == s.returnVertexID() && !visited(edges.get(i).returnEndingVertex())) { neighbours.add(edges.get(i)); } } return neighbours.get(0); // This is the minimum weight edge in the list. } ArrayList<Vertex> visited and ArrayList<Edges> graph get constructed when creating a new graph. Visited() -method is simply a boolean check to see if ArrayList visited contains the Vertex we're thinking about moving to. I tested the findClosestNeighbour() independantly and it seemed to be working but if someone finds something wrong with it then that feedback is welcome also. Mainly though as I mentioned my problem is with actually building the main loop in the Prim() -method, and if there's any additional info needed I'm happy to provide it. Thank you. Edit: To clarify what my train of thought with the Prim() method is. What I want to do is first randomize the starting point in the graph. After that, I will find the closest neighbor to that starting point. Then we'll add the edge connecting those two points to the MST, and also add the vertices to the visited list for checking later, so that we won't form any loops in the graph. Here's the error that gets thrown: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at Graph.findClosestNeighbour(graph.java:203) at Graph.Prim(graph.java:179) at MST.main(MST.java:49) Line 203: return neighbour.get(0); in findClosestNeighbour() Line 179: Edge e = findClosestNeighbour(startingVertex); in Prim()

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  • Questioning the motivation for dependency injection: Why is creating an object graph hard?

    - by oberlies
    Dependency injection frameworks like Google Guice give the following motivation for their usage (source): To construct an object, you first build its dependencies. But to build each dependency, you need its dependencies, and so on. So when you build an object, you really need to build an object graph. Building object graphs by hand is labour intensive (...) and makes testing difficult. But I don't buy this argument: Even without dependency injection, I can write classes which are both easy to instantiate and convenient to test. E.g. the example from the Guice motivation page could be rewritten in the following way: class BillingService { private final CreditCardProcessor processor; private final TransactionLog transactionLog; // constructor for tests, taking all collaborators as parameters BillingService(CreditCardProcessor processor, TransactionLog transactionLog) { this.processor = processor; this.transactionLog = transactionLog; } // constructor for production, calling the (productive) constructors of the collaborators public BillingService() { this(new PaypalCreditCardProcessor(), new DatabaseTransactionLog()); } public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) { ... } } So dependency injection may really be an advantage in advanced use cases, but I don't need it for easy construction and testability, do I?

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  • Questioning one of the arguments for dependency injection: Why is creating an object graph hard?

    - by oberlies
    Dependency injection frameworks like Google Guice give the following motivation for their usage (source): To construct an object, you first build its dependencies. But to build each dependency, you need its dependencies, and so on. So when you build an object, you really need to build an object graph. Building object graphs by hand is labour intensive (...) and makes testing difficult. But I don't buy this argument: Even without dependency injection, I can write classes which are both easy to instantiate and convenient to test. E.g. the example from the Guice motivation page could be rewritten in the following way: class BillingService { private final CreditCardProcessor processor; private final TransactionLog transactionLog; // constructor for tests, taking all collaborators as parameters BillingService(CreditCardProcessor processor, TransactionLog transactionLog) { this.processor = processor; this.transactionLog = transactionLog; } // constructor for production, calling the (productive) constructors of the collaborators public BillingService() { this(new PaypalCreditCardProcessor(), new DatabaseTransactionLog()); } public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) { ... } } So there may be other arguments for dependency injection (which are out of scope for this question!), but easy creation of testable object graphs is not one of them, is it?

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  • Structuring cascading properties - parent only or parent + entire child graph?

    - by SB2055
    I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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  • How to choose an integer linear programming solver ?

    - by Cassie
    Hi all, I am newbie for integer linear programming. I plan to use a integer linear programming solver to solve my combinatorial optimization problem. I am more familiar with C++/object oriented programming on an IDE. Now I am using NetBeans with Cygwin to write my applications most of time. May I ask if there is an easy use ILP solver for me? Or it depends on the problem I want to solve ? I am trying to do some resources mapping optimization. Please let me know if any further information is required. Thank you very much, Cassie.

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  • FusionCharts vs GoogleCharts vs HighCharts suggestions required for commercial use

    - by Forte
    I find that FusionCharts v3 evaluation and HighCharts cannot be used for commercial purpose. Google charts is the best option but those are not as good looking as any of the above. They don't even have 3d charts although their visualization API does support 3D which i cannot find. Is there any open source graphing or charting solution available which can be used in commercial products? I even looked in to Open Flash Charts 2 but found that the developer had left the project long time a go and the currently out libs are way too buggy. I had to fix more than 50 bugs to get their 1 chart working. I tried to fix others but couldn't get Pie charts etc. working. What i'm looking for is - 1. Attractive 3d column chart. 2. 3d Pie Chart. 3. Spline Chart. 4. Geographical Chart. Does anyone knows any open source or free solution which can be used for commercial products? Cheers!

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  • help with number calculation algorithm [hw]

    - by sa125
    Hi - I'm working on a hw problem that asks me this: given a finite set of numbers, and a target number, find if the set can be used to calculate the target number using basic math operations (add, sub, mult, div) and using each number in the set exactly once (so I need to exhaust the set). This has to be done with recursion. So, for example, if I have the set {1, 2, 3, 4} and target 10, then I could get to it by using ((3 * 4) - 2)/1 = 10. I'm trying to phrase the algorithm in pseudo-code, but so far haven't gotten too far. I'm thinking graphs are the way to go, but would definitely appreciate help on this. thanks.

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  • Auto Login facebook user into application

    - by user537562
    So, Here is the scenario I am trying to fix. A returning user is logged into facebook but not logged into the application. In this case when the user tries to load the application, since the user cookie is not attained yet, it redirects the user to the login page. I googled around and found this solution, FB.Event.subscribe('auth.sessionChange', function(response) { if (response.session) { window.location.reload(); } } basically whats happening here is, we are registering to facebook for a login/logout event and when it receives a response, we reload the page. Now its loads the right page since we have the user cookie on our site domain after the first load. this works, but the problem is the double load. It takes a lot of time. How can I attain the user cookie on server side for returning user? so that I don't have to do the initial page reload. Also, I have looked at yelp, and somehow they are able to load the user information without doing double load, does any body know they are able to do it? Any help is greatly appreciated, Thanks!

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  • Can't checkin to Facebook Places by post to api?

    - by MarcusJoe
    Hey everybody, I am trying to build an app where I let my registered user be able to check in to places on Facebook Places. I however for some reason can't seem to make this work. I assumed this is possible with the Api as write functionality has been added to it, but I couldn't find an clear explanation on the web. this is what I currently have, after I have asked the user for permission to publish checkins and for user_checkins. <?php require("src/facebook.php"); $facebook = new Facebook(array( 'appId' => 'xxxxxxxxx', 'secret' => 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx', 'cookie' => true )); # see if active session $session = $facebook->getSession(); if(!empty($session)) { try{ $uid = $facebook->getUser(); $api_call = array( 'method' => 'users.hasAppPermission', 'uid' => $uid, 'ext_perm' => 'publish_checkins' ); $can_post = $facebook->api($api_call); if($can_post){ $facebook->api('/'.$uid.'/checkins', 'POST', array( 'access_token' => $facebook->getAccessToken(), 'place' => 'place_id', 'message' =>'I went to placename today', 'picture' => 'http://www.place.com/logo.jpg', 'coordinates' => array( 'latitude' => 'lattiude', 'longitude' => 'lattitude', 'tags' => $uid, ) ) ); echo 'You were checked in'; } else { die('Permissions required!'); } } catch (Exception $e){} } else { # There's no active session,generate one $login_url = $facebook->getLoginUrl(); header("Location: ".$login_url); } ?> The code works when I change it 'checkins' to 'feed'. Is there something wrong with my code or am I trying to do somethign that isn't possible (or do it the wrong way). Any help will be greatly appreciated as I already spent quite a significant amount of time trying to fix this, but I just can't seem to make it work. Best regards, Marcus Joe

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  • How to send a Facebook notification through their API

    - by at
    I asked this on the Facebook Developers Forum with no responses.. How do I send notifications to users so they show up in the Notifications globe icon tab on the top left of a user's Facebook page? Some applications I use have their notifications show up there, but I don't see how that mechanism works in Facebook's API docs. Neither are there any permissions which seem to be required to send users notifications.

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  • Finding minimum cut-sets between bounded subgraphs

    - by Tore
    If a game map is partitioned into subgraphs, how to minimize edges between subgraphs? I have a problem, Im trying to make A* searches through a grid based game like pacman or sokoban, but i need to find "enclosures". What do i mean by enclosures? subgraphs with as few cut edges as possible given a maximum size and minimum size for number of vertices for each subgraph that act as a soft constraints. Alternatively you could say i am looking to find bridges between subgraphs, but its generally the same problem. Given a game that looks like this, what i want to do is find enclosures so that i can properly find entrances to them and thus get a good heuristic for reaching vertices inside these enclosures. So what i want is to find these colored regions on any given map. My Motivation The reason for me bothering to do this and not just staying content with the performance of a simple manhattan distance heuristic is that an enclosure heuristic can give more optimal results and i would not have to actually do the A* to get some proper distance calculations and also for later adding competitive blocking of opponents within these enclosures when playing sokoban type games. Also the enclosure heuristic can be used for a minimax approach to finding goal vertices more properly. A possible solution to the problem is the Kernighan-Lin algorithm: function Kernighan-Lin(G(V,E)): determine a balanced initial partition of the nodes into sets A and B do A1 := A; B1 := B compute D values for all a in A1 and b in B1 for (i := 1 to |V|/2) find a[i] from A1 and b[i] from B1, such that g[i] = D[a[i]] + D[b[i]] - 2*c[a][b] is maximal move a[i] to B1 and b[i] to A1 remove a[i] and b[i] from further consideration in this pass update D values for the elements of A1 = A1 / a[i] and B1 = B1 / b[i] end for find k which maximizes g_max, the sum of g[1],...,g[k] if (g_max > 0) then Exchange a[1],a[2],...,a[k] with b[1],b[2],...,b[k] until (g_max <= 0) return G(V,E) My problem with this algorithm is its runtime at O(n^2 * lg(n)), i am thinking of limiting the nodes in A1 and B1 to the border of each subgraph to reduce the amount of work done. I also dont understand the c[a][b] cost in the algorithm, if a and b do not have an edge between them is the cost assumed to be 0 or infinity, or should i create an edge based on some heuristic. Do you know what c[a][b] is supposed to be when there is no edge between a and b? Do you think my problem is suitable to use a multi level problem? Why or why not? Do you have a good idea for how to reduce the work done with the kernighan-lin algorithm for my problem?

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  • How to choose a integer linear programming solver ?

    - by Cassie
    Hi all, I am newbie for integer linear programming. I plan to use a integer linear programming solver to solve my combinational optimization problem. I am more familiar with C++/object oriented programming on an IDE. Now I am using NetBeans with Cygwin to write my applications most of time. May I ask if there is an easy use ILP solver for me? Or does it depend on the problem I want to solve ? I am trying to do some resources mapping optimization. please let me know if any further information is required. Thank you very much, Cassie.

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  • Python: x-y-plot with matplotlib

    - by kame
    I want to plot some data. The first column contains the x-data. But matplotlib doesnt plot this. Where is my mistake? #fresnel formula import numpy as np from numpy import cos from scipy import * from pylab import plot, show, ylim, yticks from matplotlib import * from pprint import pprint n1 = 1.0 n2 = 1.5 #alpha, beta, intensity data = [ [10, 22, 4.3], [20, 42, 4.2], [30, 62, 3.6], [40, 83, 1.3], [45, 102, 2.8], [50, 123, 3.0], [60, 143, 3.2], [70, 163, 3.8], ] for i in range(len(data)): rhotang1 = (n1 * cos(data[i][0]) - n2 * cos(data[i][1])) rhotang2 = (n1 * cos(data[i][0]) + n2 * cos(data[i][1])) rhotang = rhotang1 / rhotang2 data[i].append(rhotang) #append 4th value pprint(data) x = data[:][0] y1 = data[:][2] y3 = data[:][3] plot(x, y1, x, y3) show() EDIT: http://paste.pocoo.org/show/205534/ But it doesnt work.

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  • Implementation of any Hamiltonian Path Problem algorithm

    - by Julien
    Hi all ! Here is my problem : I have an array of points, the points have three properties : the "x" and "y" coordinates, and a sequence number "n". The "x" and "y" are defined for all the points, the "n" are not. You can access and write them calling points[i]-x, points[i]-y, points[i]-n. i.e. : points[i]->n = var var = points[i]->n So the title maybe ruined the surprise, but I'm looking for a possible implementation of a solution to the Hamiltonian path problem : I need to set the "n" number of each point, so that the sequence is the shortest path (not cycle, the edges have to be disjoint) that goes exactly once through each point. I looked for a solution and I found The Bellman Ford Algorithm but I think it doesn't work since the problem doesn't specify that it has to go through all of the points is it correct ? If it is, does somebody has another algorithm and the implementation ? If the Bellman Ford Algorithm works, how would I implement it ? Thanks a lot, Julien

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