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Search found 8262 results on 331 pages for 'optimization algorithm'.

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• Is there a class like a Dictionary without a Value template? Is HashSet<T> the correct answer?

  - by myotherme

  I have 3 tables: Foos, Bars and FooBarConfirmations I want to have a in-memory list of FooBarConfirmations by their hash: FooID BarID Hash 1 1 1_1 2 1 2_1 1 2 1_2 2 2 2_2 What would be the best Class to use to store this type of structure in-memory, so that I can quickly check to see if a combination exists like so: list.Contains("1_2"); I can do this with Dictionary<string,anything>, but it "feels" wrong. HashSet looks like the right tool for the job, but does it use some form of hashing algorithm in the background to do the lookups efficiently?

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• C++ - defining static const integer members in class definition

  - by HighCommander4

  My understanding is that C++ allows static const members to be defined inside a class so long as it's an integer type. Why, then, does the following code give me a linker error? #include <algorithm> #include <iostream> class test { public: static const int N = 10; }; int main() { std::cout << test::N << "\n"; std::min(9, test::N); } The error I get is: test.cpp:(.text+0x130): undefined reference to `test::N' collect2: ld returned 1 exit status Interestingly, if I comment out the call to std::min, the code compiles and links just fine (even though test::N is also referenced on the previous line). Any idea as to what's going on? My compiler is gcc 4.4 on Linux.

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• Scraping html WITHOUT uniquie identifiers using python

  - by Nicholas Law

  I would like to design an algorithm using python that scrapes thousands of pages like this one and this one, gathers all the data and inserts it into a MySQL database. The script will be run on a weekly or bi-weekly basis to update the database of any new information added to each individual page. Ideally I would like a scraper that is easy to work with for table structured data but also data that does not have unique identifiers (ie. id and classes attributes). Which scraper add-on should I use? BeautifulSoup, Scrapy or Mechanize? Are there any particular tutorials/books I should be looking at for this desired result? In the long-run I will be implementing a mobile app that works with all this data through querying the database.

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• How are managed the sequences by JPA and Hibernate?

  - by romaintaz

  Hi all, I am using Hibernate in my project, and many of my entities use a sequence for their technical keys. For example: @Entity @Table(name = "T_MYENTITY") @SequenceGenerator(name = "S_MYENTITY", sequenceName = "S_MYENTITY") public class MyEntity { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_MYENTITY") @Column(name = "MY_ENTITY_ID") private Long entityId; ... } I have two questions about the ID generated by Hibernate when a new object of this class is persisted: Why SequenceGenerator (from javax.persistence) has a default value of allocationSize set to 50 instead of 1? What are the interests of that? What is the default algorithm used by Hibernate to calculate the generated ID? It seems that Hibernate uses the value returned by the sequence hosted by my Oracle database, but then modify it before assigning it to my entity...

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• Architecture for analysing search result impressions/clicks to improve future searches

  - by Hais

  We have a large database of items (10m+) stored in MySQL and intend to implement search on metadata on these items, taking advantage of something like Sphinx. The dataset will be changing slightly on a daily basis so Sphinx will be re-indexing daily. However we want the algorithm to self-learn and improve search results by analysing impression and click data so that we provide better results for our customers on that search term, and possibly other similar search terms too. I've been reading up on Hadoop and it seems like it has the potential to crunch all this data, although I'm still unsure how to approach it. Amazon has tutorials for compiling impression vs click data using MapReduce but I can't see how to get this data in a useable format. My idea is that when a search term comes in I query Sphinx to get all the matching items from the dataset, then query the analytics (compiled on an hourly basis or similar) so that we know the most popular items for that search term, then cache the final results using something like Memcached, Membase or similar. Am I along the right lines here?

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• How to find the entity with the greatest primary key?

  - by simpatico

  I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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• android spectrum analysis of streaming input

  - by TheBeeKeeper

  for a school project I am trying to make an android application that, once started, will perform a spectrum analysis of live audio received from the microphone or a bluetooth headset. I know I should be using FFT, and have been looking at moonblink's open source audio analyzer ( http://code.google.com/p/moonblink/wiki/Audalyzer ) but am not familiar with android development, and his code is turning out to be too difficult for me to work with. So I suppose my questions are, are there any easier java based, or open source android apps that do spectrum analysis I can reference? Or is there any helpful information that can be given, such as; steps that need be taken to get the microphone input, put it into an fft algorithm, then display a graph of frequency and pitch over time from its output? Any help would be appreciated, thanks.

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• Animate a e.Graphics.DrawLine with arrowhead

  - by Fer

  I need to "animate" an arrow. It can go in any direction (up, down, left, right and diagonals) and the arrowhead will be at the end. It needs to appear as if it is growing from orgin to the end. To make matters more complicated it has to be in a user control so it is possible to add to the controls collection in the forms and remove it to delete it from the screen, and its background is really transparent (no color.transparent) so i can't paint the background to "clear" the previous line. I have it static already (drawn from origin to end) but i can't animate it. I tried to add a timer in the user control but I fail to get a correct algorithm to calculate the intermediate ends of the line while it is growing. Any help would be appreciated. Thanks

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• Quick-sort doesn't work with middle pivot element

  - by Bobby

  I am trying to sort an array of elements using quick-sort algorithm.But I am not sure where am I going wrong.I choose the middle element as pivot every time and then I am checking the conditions.Here is my code below. void quicksort(int *temp,int p,int r) { if(r>p+1) { int mid=(p+r)/2; int piv=temp[mid]; int left=p+1; int right=r; while(left < right) { if(temp[left]<=piv) left++; else swap(&temp[left],&temp[--right]); } swap(&temp[--left],&temp[p]); quicksort(temp,p,left); quicksort(temp,right,r); } }

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• Random numbers from binomial distribution

  - by Sarah

  I need to generate quickly lots of random numbers from binomial distributions for dramatically different trial sizes (most, however, will be small). I was hoping not to have to code an algorithm by hand (see, e.g., this related discussion from November), because I'm a novice programmer and don't like reinventing wheels. It appears Boost does not supply a generator for binomially distributed variates, but TR1 and GSL do. Is there a good reason to choose one over the other, or is it better that I write something customized to my situation? I don't know if this makes sense, but I'll alternate between generating numbers from uniform distributions and binomial distributions throughout the program, and I'd like for them to share the same seed and to minimize overhead. I'd love some advice or examples for what I should be considering.

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• aspx page gives viewstate error

  - by Priya10

  Hi, I have a simple aspx page with one grid view. When deployed on server, and accessed through that machine, it works fine. However, when connected through load balancer, we get this error ( when click on any button). The page however refreshes when pressed F5. Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. Any idea what is happening here???

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• Parsing String to TreeNode

  - by Krusu70

  Anyone have a good algorithm how to parse a String to TreeNode in Java? Let's say we have a string s which says how to build a TreeNode. A(B,C) means that A is the name (String) of TreeNode, B is child of A (Treenode), C is sibling of A (TreeNode). So if I call function with string A(B(D,E(F,G)),C) (just a example), then I get a TreeNode equals to: level A (String: name), B - Child (TreeNode), C - Sibling (TreeNode) level B (String: name), D - Child of B (TreeNode), E - Sibling of B (TreeNode) level E (String: name), F - Child of E (TreeNode), G - Sibling of E (TreeNode) The name may not be 1 letter, it could be like real name (many letters).

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• Update NSView in function of events

  - by Forchita

  Hi everyone! I have a main view (subclass of NSView) and as i'm new to cocoa, i'd like to know how to update the view in function of events. I know there are many methods that take events such as -(void)mouseMoved:(NSEvent*)event or - (void)mouseClicked:(NSEvent*)event My algorithm to determine what to do is ready. I want to know where I should update the main view: is it in the -(void)mouseMoved:(NSEvent*)event or in the - (void)drawRect:(NSRect)dirtyRect. And if it is in drawRect, then how should i pass the information to it? Thanks in advance!

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• Is it possible to manipulate the format on a DataGridView that is bound to a Data Source?

  - by Jack Johnstone

  I´m using SQL Server 2005 and Visual Studio 2008, C#. In the data source (the SQL Server data table) I use the date format mm/dd/yyyy, however, in a forms overview (DataGridView) users would like to see a completely other format, with year, week number and day number of week (yyww,d). I´ve created an algorithm for this transformation, but can I populate the affected cells with yyww,d instead of mm/dd/yyyy? And in that case - how would I do it? I guess I need to do it after the cells are populated, but before they are shown. The generic question is - how do I manipulate the format of Data Source bound DataGridView cells.

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• Visual C++ 9 Linker file size limitation.

  - by Raindog

  It appears that the visual C++ 9 linker has a file allocation algorithm that doubles the size of the file every allocation, so you get 512mb, 1024mb, 2048mb, 4096mb. The problem is that it is using a library that cannot handle files larger 2048MB, and as such crashes with an error such as "cannot read file at is the disk full or write protected". Is there a way to bypass this limitation or otherwise replace the linker with something else that works? A bit of background, I have a code generator that generates a large number of files, ~15k cpp files, I've managed to reduce the number of files to something about 6k to get something that at least completes the linking process, I would like to be able to include all 15k without having to create multiple libs.

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• kmeans based on mapreduce by python

  - by user3616059

  I am going to write a mapper and reducer for the kmeans algorithm, I think the best course of action to do is putting the distance calculator in mapper and sending to reducer with the cluster id as key and coordinates of row as value. In reducer, updating the centroids would be performed. I am writing this by python. As you know, I have to use Hadoop streaming to transfer data between STDIN and STOUT. according to my knowledge, when we print (key + "\t"+value), it will be sent to reducer. Reducer will receive data and it calculates the new centroids but when we print new centroids, I think it does not send them to mapper to calculate new clusters and it just send it to STDOUT and as you know, kmeans is a iterative program. So, my questions is whether Hadoop streaming suffers of doing iterative programs and we should employ MRJOB for iterative programs?

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• function to efficiently check a change of value in a nested hashmap

  - by zcaudate

  the motivation is for checking what has changed in a deeply nest map, kind of like a reverse of update-in. This is a simple example: (def p1 {:a {:a1 :1 :a2 :2} :b {:b1 :1 :b2 :2}}) (def p2 (update-in p1 [:a :a1] (constantly :updated)) ;; => {:a {:a1 :updated :a2 :2} ;; :b {:b1 :1 :b2 :2}} (what-changed? p1 p2) ;; => {:keys [:a :a1] :value :updated) (what-changed? p2 p1) ;; => {:keys [:a :a1] :value :2) I'm hoping that because clojure maps are persistent data-structures, there may be a smart algorithm to figure this out by looking at the underlying structure as opposed to walking through the nested maps and comparing the difference.

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• Validation of viewstate MAC failed in Safari

  - by Midhat

  Hi I have a web app using forms authentication. When I perform the following steps Let the login cookie expire Click on a link that requires a logged in user The user is redirected to the login page Click the browser back button The user is redirected to the login page again Log in using a valid username/password I get this exception Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. This case appears only in safari (windows and mac). The fundamental difference between safari and other browsers is that when we click the back button in step 4, safari shows the login page again, while the other browsers show the previous page the user was working on. Please help in this regard

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• Beginner C: error: control reaches end of non-void function?

  - by Ting

  I'm trying to make a greedy algorithm and I get this error: greedy2.c:27:1: error: control reaches end of non-void function [-Werror,-Wreturn-type] } ^ 1 error generated. with this code: int man(int argc, char* argv[]) { float amount; do { printf("Input dollar amount owed:\n"); amount = GetFloat(); } while (amount <= 0); int coins = 0; while (amount >= 0.25); { amount = amount - 0.25; coins++; } printf("Number of coins to use: %d\n", coins); } What is wrong with my curly braces, and how do I fix it?

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• How can I add floats together in different orders, and always get the same total?

  - by splicer

  Let's say I have three 32-bit floating point values, a, b, and c, such that (a + b) + c != a + (b + c). Is there summation algorithm, perhaps similar to Kahan summation, that guarantees that these values can be summed in any order and always arrive at the exact same (fairly accurate) total? I'm looking for the general case (i.e. not a solution that only deals with 3 numbers). Is arbitrary precision arithmetic the only way to go? I'm dealing with very large data sets, so I'd like to avoid the overhead of using arbitrary precision arithmetic if possible. Thanks!

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• Correct expression for checking leap years

  - by Debanjan

  What will be the exact definition of leap year? AFAIK "A year which is divisible by 4 is a leap year. But for century years' the years which are divisible by 400 is a leap year." But that definition makes 100, 200, 300, 400.... upto 1700 NOT LEAP years! But in Gregorian calendar all of them are all leap year, check this out. You can also try "call 1700" in Linux to verify. So the correct algorithm for leap years would be: if ( (year % 4 == 0) && ( year <= 1700 || year % 100 != 0 || year % 400 == 0 )) printf("%d is a leap year.\n", year); else printf("%d is not a leap year.\n", year); But is this specific to Gregorian calendar? Even if that is the case why is it not mentioned here? Regards, PS:The history of Gregorian callender seems interesting check out the September month of 1752.

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• Using my ISerializable implementation instead of DataContractSerializer

  - by mpm

  My WCF client and server exchange objects whose types are defined on a class library shared by both, the server and the client. These objects implement custom serialization via ISerializable. However, my custom serialization is not being used. DataContractSerializer is being used, instead. How do I force my custom serialization to be used? The reason why I need to use my own serialization is because I do trasfer some big object graphs and my serialization algorithm does a good job in compressing/speeding up things.

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• Deleting Part of An Array in Java to Free Memory on Heap

  - by kate

  I am implementing a dynamic programming algorithm for the knapsack problem in Java. I declare the array and then initialize its size to be [number of objects][capacity of knapsack]. When my number of objects or my capacity gets too large, I get a memory error because I run out of space on the heap. My questions is: If I delete rows from my double array as I go along, will Java free the memory as I delete? Or does Java reserve that memory space for the size of the array I originally created? If it's the latter, is there a way to manually free the memory in Java? Thanks for your Help!

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• Getting Factors of a Number

  - by Dave

  Hi Problem: I'm trying to refactor this algorithm to make it faster. What would be the first refactoring here for speed? public int GetHowManyFactors(int numberToCheck) { // we know 1 is a factor and the numberToCheck int factorCount = 2; // start from 2 as we know 1 is a factor, and less than as numberToCheck is a factor for (int i = 2; i < numberToCheck; i++) { if (numberToCheck % i == 0) factorCount++; } return factorCount; }

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• Disposing a Bitmap through its Finalizer

  - by devoured elysium

  I have a complex program in which I have to first create, then use wrappers around bitmaps and send them across a lot of different classes. The problem in the end is deciding which classes should dispose the bitmaps. Most of the time the end classes don't know if they can indeed dispose the bitmap as the same bitmap can be used in several places. Also, I can't just copy the bitmaps because this is a kind of resource intensive algorithm and doing it would be dead slow. I looked up on reflector for Image/Bitmap's implementations and they seem to use the Dispose Pattern. So, even if I don't call Dispose(), the CLR will eventually call it some other time. Is it too bad if I just let the bitmaps be as they are, and let the finalizer take care of them?

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