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• Cone-Line Segment Intersection 2D

  - by nophnoph

  Hi everyone, I would like to know is there any way to determine if a cone is intersecting with a (finite)line segment. The cone actually a circle located at P(x,y) with theta degree field of view and radius r. The simple visualization can be found here (sorry i can't post the picture here) I'm trying to do it in C# but I don't have any idea how to that, so for now this is what I'm doing : Check if the line segment is intersecting with the circle If the line segment is intersecting with the circle then I check every single point in the line segment using a function I found here. But I don't think this is the best way to do it. Does anyone have an idea? For additional info, I need this function to make some kind of simple vision simulator. Thanks in advance :)

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• Django - Check users messages every request

  - by Hanpan

  Hi, I want to check if a user has any new messages each time they load the page. Up until now, I have been doing this inside of my views but it's getting fairly hard to maintain since I have a fair number of views now. I assume this is the kind of thing middleware is good for, a check that will happen every single page load. What I need it to do is so: Check if the user is logged in If they are, check if they have any messages Store the result so I can reference the information in my templates Has anyone ever had to write any middleware like this? I've never used middleware before so any help would be greatly appreciated.

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• static images aren't caching with php-generated page

  - by scootklein

  Our website was just converted to being generated by mod_rewrite and php scripts. Images aren't caching in browsers when they seemingly should be. All images follow format: <img src="/images/header.png" /> I must avoid the script completely caching because the PHP parser needs to handle each page dynamically on each request; however, the download overhead of the large images is cumbersome on every single page load. I would ideally provide headers for "Cache-Control: no-cache, must-revalidate" and "Expires: some_date_in_the_past" to force revalidation of the PHP script. Why isn't the browser caching static images with consistent href values across all pages?

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• How to store Hierarchical K-Means tree for a large number of images, using Opencv?

  - by AquaAsh

  I am trying to make a program that will find similar images from a dataset of images. The steps are 1)extract SURF descriptors for all images 2)store the descriptors 3)Apply knn on the stored descriptors 4)Match the stored descriptors to the query image descriptor using KNN Now each images SURF descriptor will be stored as Hierarchical k means tree, now do I store each tree as a separate file or is it possible to build some sort of single tree with all the images descriptors and updated as images are added to dataset. This is the paper I am basing the program on www.ijest.info/docs/IJEST10-02-03-13.pdf.

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• How to copy QT folder to another folder without reinstalling it?

  - by Oleg

  I have QT installed on disc D (on Windows). And I want to move it to disc C. Is it possible to do that? If I just copy QT folder from C to D then I see lot of errors when I compile my applications that use QT. Errors are because qmake.exe contains full paths to include, bin and libs folders inside. So, when I create solution for Visual Studio 2005 using qmake - then this solution contains dependencies to old QT folder from disc D. And I found no way how to remove this dependencies without reinstalling of QT. It is not a big problem for one my single machine - I can reinstall. But I need to deliver this change then to tens and hundreds of other developers machines and I want to make it as easy as possible without need to reinstall QT.

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• What's the best way to implement one-dimensional collision detection?

  - by cyclotis04

  I'm writing a piece of simulation software, and need an efficient way to test for collisions along a line. The simulation is of a train crossing several switches on a track. When a wheel comes within N inches of the switch, the switch turns on, then turns off when the wheel leaves. Since all wheels are the same size, and all switches are the same size, I can represent them as a single coordinate X along the track. Switch distances and wheel distances don't change in relation to each other, once set. This is a fairly trivial problem when done through brute force by placing the X coordinates in lists, and traversing them, but I need a way to do so efficiently, because it needs to be extremely accurate, even when the train is moving at high speeds. There's a ton of tutorials on 2D collision detection, but I'm not sure the best way to go about this unique 1D scenario.

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• What is the effect on record size of reordering columns in PostgreSQL?

  - by Summer

  Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. So, what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did before? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• Amazon EC2 prices for Windows Instance?

  - by Abhishek Gupta

  Hello Guys , I want to ask from some Amazon cloud technology Experts , that is it profitable to deploy our web application on amazon cloud as compared to normal server? Currently there are micro,small, large and other types of instances available , if we start from micro instance then we realize that our app needs some more CPU cycle and Ram then how can we dynamically move to next more powerful instance automatically at runtime. What is the approx minimum yearly cost for a single EC2 windows small instance? I wnat to deploy a simple Online quiz application (ASP.net based) on Amazon Cloud which at a time can have maximum of 500 users only. Please suggest me as I m very new to Cloud .Should I go for Azure or Amazon?

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• mismatchedtoken with antlr syntactic predicates

  - by varzan

  I have the following lexer rules in my grammar file: LINE : 'F' | 'G'; RULE : (('->' ('F' | 'G')) => 'F' | 'G' ) | LINE LINE + | LINE * (ROTATE + LINE+)+ ; fragment ROTATE : ('/' | '\\'); I'm basically trying to match productions that look like F - F/F\F\F/F. It successfully matches stuff like the above, but I'm guessing there's a problem with my syntactic predicate, since G - G produces a MismatchedTokenException. The predicate serves to disambiguate between single letters on the lhs of '-', which I want to be recognized as the LINE token, and those on the rhs, which should be RULEs. Any idea what I'm doing wrong?

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• Can I do everything in C that C++ and C# and Java can do?

  - by Sahat

  Is it possible to write in C programming language everything that you could write in other languages such as Java, C# or C++. If that's the case why don't schools these days teach C instead of Java? Ok the main reason why I am asking is because I don't want to tie down to a single programming language and platform (.NET and C# or Obj-C and Cocoa). Perhaps I am confusing a programming language with a framework? If anyone could clarify all this for me, I'd certainly vote for your answer.

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• Ensuring all waiting threads complete

  - by Daniel

  I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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• Construct A Polygon Out of Union of Many Polygons

  - by Ngu Soon Hui

  Supposed that I have many polygons, what is the best algorithm to construct a polygon--maybe with holes- out of the union of all those polygons? For my purpose, you can imagine each piece of a polygon as a jigsaw puzzle piece, when you complete them you will get a nice picture. But the catch is that a small portion <5% of the jigsaw is missing, and you are still require to form a picture as complete as possible; that's the polygon-- maybe with holes-- that I want to form. My naive approach is to take two polygons, union them, and take another polygon, union it with the union of the two polygons, and repeat this process until every single piece is union. Then I will run through the union polygon list and check whether there are still some polygons can be combined, and I will repeat this process until a satisfactory result is achieved. But this seems to be like an extremely naive approach. I just wonder is there any other better algorithm?

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• Using indentation to make CSS more readable? (making parents and children more identifiable in CSS)

  - by janoChen

  I've been always guiding myself with the following CSS structure: #nav { } #nav li { } #nac li a { } This structure tells me clearly who is the parent and the child. But in a recent article (I think it was CSS Trick) someone said that CSS is read from right to left. So the more tags I had the slower it will be (and sometimes I think its unnecessary to write every single tag involve in the selector). So it may be something like this: #nav { } #special-link { } where #special-link is #nav's child. I know this is not a big problem in a simple stylesheet but in a big one I always would get confused about who is who's parent and child. Another solution would be: #nav { } #special-link { } Indentation How do you solve with this CSS dilemma?

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• Case insensitive expectations in Rhino Mocks

  - by user313886

  I'm using Rhino Mocks to expect a call. There is a single parameter which is a string. But I'm not bothered about the case of the string. I want the test to pass even if the case is wrong. So I'm doing the following: //expect log message to be called with a string parameter. //We want to ignore case when verifiyig so we use a constraint instead of a direct parameter Expect.Call(delegate { logger.LogMessage(null); }).Constraints(Is.Matching<string>(x => x.ToLower()=="f2")); It seems a bit log winded. Is there a more sensible way of doing this?

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• Finding mySQL duplicates, then merging data

  - by Michael Pasqualone

  I have a mySQL database with a tad under 2 million rows. The database is non-interactive, so efficiency isn't key. The (simplified) structure I have is: `id` int(11) NOT NULL auto_increment `category` varchar(64) NOT NULL `productListing` varchar(256) NOT NULL Now the problem I would like to solve is, I want to find duplicates on productListing field, merge the data on the category field into a single result - deleting the duplicates. So given the following data: +----+-----------+---------------------------+ | id | category | productListing | +----+-----------+---------------------------+ | 1 | Category1 | productGroup1 | | 2 | Category2 | productGroup1 | | 3 | Category3 | anotherGroup9 | +----+-----------+---------------------------+ What I want to end up is with: +----+----------------------+---------------------------+ | id | category | productListing | +----+----------------------+---------------------------+ | 1 | Category1,Category2 | productGroup1 | | 3 | Category3 | anotherGroup9 | +----+----------------------+---------------------------+ What's the most efficient way to do this either in pure mySQL query or php?

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• Looking for suggestions about an architecture of a MultiThreaded app.

  - by Dimitri

  Hello everyone. I am looking to develop a multithreaded application that will be running in unconditional loop and processing high volume of data. High volume is 2000+ records per minute. Processing will involve data retrieval, calculations and data updates. I need the application to perform so that there is virtually no back log, meaning i need to be able to finish up all of the 2000 points in one minute or even faster. Our current implementation features a multithreaded application that is spawn multiple times (from 10 to 20) and we are noticing that it's not handling data as expected and i even feel that instances of the application compete with each other for processor time and eventually if not slowing, not benefiting each other for sure. I would like to know what would be the best approach: have a single instance running but maximize threads that can run simultaneously? or is there other ways i don't know? I'm open to suggestions. Thank you in advance

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• question about missing element in array

  - by davit-datuashvili

  i have following problem from book introduction algorithm second edition by MIT university problem is following An array A[1 . . n] contains all the integers from 0 to n except one. It would be easy to determine the missing integer in O(n) time by using an auxiliary array B[0 . . n] to record which numbers appear in A. In this problem, however, we cannot access an entire integer in A with a single operation. The elements of A are represented in binary, and the only operation we can use to access them is “fetch the j th bit of A[i],” which takes constant time. Show that if we use only this operation, we can still determine the missing inte- ger in O(n) time please help

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• web page db query optimisation

  - by morpheous

  I am putting together a web page which is quite 'expensive' in terms of Db hits. I dont want to start optimizing at this stage - though with me trying to hit a deadline, I may end up not optimising at all. Currently the page requires 18 (thats right eighteen) hits to the db. I am already using joins, and some of the queries are UNIONed to minimize the trips to the db. My local dev machine can handle this (page is not slow) however, I feel if I release this into the wild, the number of queries will quickly overwhelm my database (mySQL). I could always use memcache or something similar, but I would much rather continue with my other dev work that needs to be completed before the deadline - at least retrieving the page work, its simply a matter of optimization. My question therefore is - is 18 db queries for a single page retrieval completely outrageous - (i.e. I should put everything on hold and optimize the hell of the retrieval logic), or shall I continue as normal, meet the deadline and release on schedule and see what happens?

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• How to create and restore a backup from SqlAlchemy?

  - by swilliams

  I'm writing a Pylons app, and am trying to create a simple backup system where every table is serialized and tarred up into a single file for an administrator to download, and use to restore the app should something bad happen. I can serialize my table data just fine using the SqlAlchemy serializer, and I can deserialize it fine as well, but I can't figure out how to commit those changes back to the database. In order to serialize my data I am doing this: from myproject.model.meta import Session from sqlalchemy.ext.serializer import loads, dumps q = Session.query(MyTable) serialized_data = dumps(q.all()) In order to test things out, I go ahead and truncation MyTable, and then attempt to restore using serialized_data: from myproject.model import meta restore_q = loads(serialized_data, meta.metadata, Session) This doesn't seem to do anything... I've tried calling a Session.commit after the fact, individually walking through all the objects in restore_q and adding them, but nothing seems to work. What am I missing? Or is there a better way to do what I'm aiming for? I don't want to shell out and directly touch the database, since SqlAlchemy supports different database engines.

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• Using Remote Web Page to Initialize iPhone App

  - by Chris_K

  My iPhone app relies on a vendor's XML feed to provide data. But that feed is not locked down. The vendor could change the format of the XML at any time, although so far they've promised not to. Since I might want to tell my app to use a different URL for its data source, I'd like to set up a single "Command Central" Web page, on my own server, to direct the app to the correct data source. In other words, each time my app starts, in the background and unseen by the user, it would visit "http://www.myserver.com/iphoneapp_data_sources.xml" to retrieve the URL for retrieving data from my vendor. That way, if my vendor suddenly changes the exact URL or the XML feed that the app needs, I can update that Web page and ensure that all installations of the app are using the correct XML feed. Does anyone have any advice or examples showing this kind of approach? It seems as if this must be a common problem, but so far I haven't found a well-established design pattern that fits it.

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• GWT SE friendly application

  - by user180152

  Hi friends, How I can develop 'Search Engine Friendly' web app in GWT? Take an example of StackOverflow it self, its a web app and should be SEO friendly allowing user to search from search engine. If some one want to develope same app in GWT. How one can make it SEO friendly? As GWT contain a single HTML file. How we can allow its inner content to be visible in SE? Any suggestion or comment, will really help. Thank you.

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• Scanner's Read Line returning NoSuchElementException

  - by Brian

  This is my first time using StackOverflow. I am trying to read a text file which consists of a single number one the first line. try { Scanner s = new Scanner(new File("HighScores.txt")); int temp =Integer.parseInt(s.nextLine()); s.close(); return temp; } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } However, I get an error: java.util.NoSuchElementException: No line found at java.util.Scanner.nextLine(Unknown Source) at GameStart.getHighScore(GameStart.java:334) at GameStart.init(GameStart.java:82) at sun.applet.AppletPanel.run(Unknown Source) at java.lang.Thread.run(Unknown Source) I know that HighScores.txt is not empty, so why is this problem occuring? I tried using BufferedReader, and BufferReader.readLine() return null.

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• In C, is it possible do free only an array first or last position?

  - by user354959

  Hi there! I've an array, but I don't need its first (or last) position. So I point a new variable to the rest of the array, but I should free the array first/last position. For instance: p = read_csv_file(); q = p + 1; // I don't need the first CSV file field // Here I'd like to free only the first position of p return q; Otherwise I've to memcpy the array to other variable, excluding the first position, and then free the original array. Like this: p = read_csv_file(); q = (int*) malloc(sizeof(int) * (SOME_SIZE - 1)); memcpy(q, p+1, sizeof(int) * (SOME_SIZE - 1)); free(p); return q; But then I'll have the overhead of copying all the array. Is this possible to only free a single position of an array?

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• How do you encode an apostrophe so that it's searchable in mysql?

  - by Yegor

  I don't think that was the most clear question, but an example should make it a little clearer. I have a table filled with movie names, some of which contain apostrophes. I have a search box which is used to find movies. If I perform searches via mov_title = '$search_keywords' it all works, but this method will not yield any results for partial searches, so I have to use this mov_title LIKE '%$search_keywords%' This method works fine for titles that are A-Za-z0-9, but if a title has an apostrophe, it's not able to find the movie, even if I do an exact match. Before the titles are stored in the DB, I put them through this: $search_keywords = htmlspecialchars(mysql_escape_string($_GET["search_keywords"])); So in the DB, there is a forward slash before every single apostrophe. The only way to match a movie title with an apostrophe is to physically put a forward slash in front of the apostrophe, in the search box. This seems so trivial, and I'm sure the solution is painfully obvious, but I'm just not seeing it.

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• Is there a database with git-like qualities?

  - by Mat

  I'm looking for a database where multiple users can contribute and commit new data; other users can then pull that data into their own database repository, all in a git-like manner. A transcriptional database, if you like; does such a thing exist? My current thinking is to dump the database to a single file as SQL, but that could well get unwieldy once it is of any size. Another option is to dump the database and use the filesystem, but again it gets unwieldy once of any size.

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