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  • How to calculate square root in PHP [explained] [on hold]

    - by Enes Imsirovic
    At first code ! Don't forget embed the JQuery ! <html> <head> <title>Simple jQuery and PHP Square Root example</title> <script src="js/jquery-1.10.1.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function() { $('#form').submit(function(){ var number = $('#number').val(); $.ajax({type:"post",url:"calculate.php",data:"number=" +number,success:function(msg){$('#result').hide(); $("#result").html("<h3>" + msg + "</h3>").fadeIn("slow"); } }); return false; }); }); </script> </head> <body> <form id="form" action="calculate.php" method="post"> Enter number: <input id="number" type="text" name="number" /> <input id="submit" type="submit" value="Calculate Square Root" name="submit"/> </form> <p id="result"></p> </body> </html> Second code witch would be connected with first : calculate.php <?php if($_POST['number']==null){ echo "Please Enter a Number"; }else { if (!is_numeric($_POST['number'])) { echo "Please enter only numbers"; }else{ echo "Square Root of " .$_POST['number'] ." is ".sqrt($_POST['number']); } } ?> Chiefly for begginers, to see the power of PHP :) xD Load this on your localhost.. PHP files and JS : https://mega.co.nz/#!Et8zWSBb!KX2PFxa2Pzw_l-wi6QU8xi_eKTlHbtQuBsT_DvXrifk At least it look like this : http://imgur.com/vNnDRQ3

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  • What is a good design pattern / lib for iOS 5 to synchronize with a web service?

    - by Junto
    We are developing an iOS application that needs to synchronize with a remote server using web services. The existing web services have an "operations" style rather than REST (implemented in WCF but exposing JSON HTTP endpoints). We are unsure of how to structure the web services to best fit with iOS and would love some advice. We are also interested in how to manage the synchronization process within iOS. Without going into detailed specifics, the application allows the user to estimate repair costs at a remote site. These costs are broken down by room and item. If the user has an internet connection this data can be sent back to the server. Multiple photographs can be taken of each item, but they will be held in a separate queue, which sends when the connection is optimal (ideally wifi). Our backend application controls the unique ids for each room and item. Thus, each time we send these costs to the server, the server echoes the central database ids back, thus, that they can be synchronized in the mobile app. I have simplified this a little, since the operations contract is actually much larger, but I just want to illustrate the basic requirements without complicating matters. Firstly, the web service architecture: We currently have two operations: GetCosts and UpdateCosts. My assumption is that if we used a strict REST architecture we would need to break our single web service operations into multiple smaller services. This would make the services much more chatty and we would also have to guarantee a delivery order from the app. For example, we need to make sure that containing rooms are added before the item. Although this seems much more RESTful, our perception is that these extra calls are expensive connections (security checks, database calls, etc). Does the type of web api (operation over service focus) determine chunky vs chatty? Since this is mobile (3G), are we better handling lots of smaller messages, or a few large ones? Secondly, the iOS side. What is the current advice on how to manage data synchronization within the iOS (5) app itself. We need multiple queues and we need to guarantee delivery order in each queue (and technically, ordering between queues). The server needs to control unique ids and other properties and echo them back to the application. The application then needs to update an internal database and when re-updating, make sure the correct ids are available in the update message (essentially multiple inserts and updates in one call). Our backend has a ton of business logic operating on these cost estimates. We don't want any of this in the app itself. Currently the iOS app sends the cost data, and then the server echoes that data back with populated ids (and other data). The existing cost data is deleted and the echoed response data is added to the client database on the device. This is causing us problems, because any photos might not have been sent, but the original entity tree has been removed and replaced. Obviously updating the costs tree rather than replacing it would remove this problem, but I'm not sure if there are any nice xcode libraries out there to do such things. I welcome any advice you might have.

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  • Confusion with floats converted into ints during collision detection

    - by TheBroodian
    So in designing a 2D platformer, I decided that I should be using a Vector2 to track the world location of my world objects to retain some sub-pixel precision for slow-moving objects and other such subtle nuances, yet representing their bodies with Rectangles, because as far as collision detection and resolution is concerned, I don't need sub-pixel precision. I thought that the following line of thought would work smoothly... Vector2 wrldLocation; Point WorldLocation; Rectangle collisionRectangle; public void Update(GameTime gameTime) { Vector2 moveAmount = velocity * (float)gameTime.ElapsedGameTime.TotalSeconds wrldLocation += moveAmount; WorldLocation = new Point((int)wrldLocation.X, (int)wrldLocation.Y); collisionRectangle = new Rectangle(WorldLocation.X, WorldLocation.Y, genericWidth, genericHeight); } and I guess in theory it sort of works, until I try to use it in conjunction with my collision detection, which works by using Rectangle.Offset() to project where collisionRectangle would supposedly end up after applying moveAmount to it, and if a collision is found, finding the intersection and subtracting the difference between the two intersecting sides to the given moveAmount, which would theoretically give a corrected moveAmount to apply to the object's world location that would prevent it from passing through walls and such. The issue here is that Rectangle.Offset() only accepts ints, and so I'm not really receiving an accurate adjustment to moveAmount for a Vector2. If I leave out wrldLocation from my previous example, and just use WorldLocation to keep track of my object's location, everything works smoothly, but then obviously if my object is being given velocities less than 1 pixel per update, then the velocity value may as well be 0, which I feel further down the line I may regret. Does anybody have any suggestions about how I might go about resolving this?

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  • Can a candidate be judged by asking to write a complex program on "paper"?

    - by iammilind
    Sometime back in an interview, I was asked to write following program: In a keypad of a mobile phone, there is a mapping between number and characters. e.g. 0 & 1 corresponds to nothing; 2 corresponds to 'a','b','c'; 3 corresponds to 'd','e','f'; ...; 9 corresponds to 'w','x','y','z'. User should input any number (e.g. 23, 389423, 927348923747293) and I should store all the combinations of these character mapping into some data structure. For example, if user enters "23" then possible character combinations are: ad, ae, af, bd, be, bf, cd, ce, cf or if user enters, "4676972" then it can be, gmpmwpa, gmpmwpb, ..., hnroxrc, ..., iosozrc Interviewer told that people have written code for this within 20-30 mins!! Also he insisted I have to write on paper. If I am writing a code then my tendency is as of I am writing production code, even though it may not be expected from me. So, I always try to think all the aspects like, optimization, readability, maintainability, extensible and so on. Considering all these, I felt that I should be writing on PC and it needs decent 2 hours. Finally after 25 mins, I was able to come up with just the concept and some shattered pieces of code (not to mention of my rejection). My question is not the answer for the above program. I want to know that is this a right way to judge the caliber of a person ? Am I wrong / too slow in the estimates ? Am I too idealistic ?

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  • Ubuntu One has high CPU usage but no syncing

    - by Peter
    over the weekend I updated my computer to Windows 8. So far Ubuntu One was running smoothly, but ever since the update (clean, new install) Ubuntu doesn't sync any more. In Windows 7 it would start to sync at full internet speed as soon as I drop a file. But now in Windows 8, as soon as I drop a new file into the Ubuntu One folder, CPU usage goes up to about 50 % and no network traffic occurs. This stays like that for a couple of minutes, CPU usage goes back to normal and then the client says that all is in sync - which isn't true. Is it too early for Windows 8? Do others have the same problem or is there something I can do about it? I try a couple of different things, and realized that if the file size is 20 MB the files get uploaded. The original file was 1.5 GB. I also didn't work with 200, 100 and 50 MB large files. But even with 20 MB large files, the upload is very slow and not steady. The log give plenty of this error: - twisted - ERROR - Failure: exceptions.TypeError About which I don't know the meaning. By the way, the account works just fine on the Ubuntu 12.04 partition. Any help is greatly appreciated. -Peter

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  • How to debug lack of sound in Asus EEE PC

    - by Kalmar
    I have an Asus EEE PC 1225B with fresh Lubuntu 12.04. And no sound. It doesn't seem to be some common problem, so I have to make some research what's up. I tried running alsamixer, so I know I have Realtek ALC269VB with nothing muted unexpectedly. What can I do next to identify and solve the problem? Additional info: alsamixer shows two cards: HD-Audio Generic and HDA ATI-SB (Realtek ALC269VB); the first one is muted. ~$ aplay ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave aplay: main:682: blad otwierania audio: Nie ma takiego pliku ani katalogu The Polish part can be translated as "error opening audio: There is no such file or directory". ~$ sudo lspci -v | grep -A7 -i "audio" 00:01.1 Audio device: Advanced Micro Devices [AMD] nee ATI Wrestler HDMI Audio [Radeon HD 6250/6310] Subsystem: ASUSTeK Computer Inc. Device 103b Flags: bus master, fast devsel, latency 0, IRQ 44 Memory at feb44000 (32-bit, non-prefetchable) [size=16K] Capabilities: [50] Power Management version 3 Capabilities: [58] Express Root Complex Integrated Endpoint, MSI 00 Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+ Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?> -- 00:14.2 Audio device: Advanced Micro Devices [AMD] nee ATI SBx00 Azalia (Intel HDA) (rev 40) Subsystem: ASUSTeK Computer Inc. Device 103b Flags: bus master, slow devsel, latency 32, IRQ 16 Memory at feb40000 (64-bit, non-prefetchable) [size=16K] Capabilities: [50] Power Management version 2 Kernel driver in use: snd_hda_intel Kernel modules: snd-hda-intel

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  • Android 2D terrain scrolling

    - by Nikola Ninkovic
    I want to make infinite 2D terrain based on my algorithm.Then I want to move it along Y axis (to the left) This is how I did it : public class Terrain { Queue<Integer> _bottom; Paint _paint; Bitmap _texture; Point _screen; int _numberOfColumns = 100; int _columnWidth = 20; public Terrain(int screenWidth, int screenHeight, Bitmap texture) { _bottom = new LinkedList<Integer>(); _screen = new Point(screenWidth, screenHeight); _numberOfColumns = screenWidth / 6; _columnWidth = screenWidth / _numberOfColumns; for(int i=0;i<=_numberOfColumns;i++) { // Generate terrain point and put it into _bottom queue } _paint = new Paint(); _paint.setStyle(Paint.Style.FILL); _paint.setShader(new BitmapShader(texture, Shader.TileMode.REPEAT, Shader.TileMode.REPEAT)); } public void update() { _bottom.remove(); // Algorithm calculates next point _bottom.add(nextPoint); } public void draw(Canvas canvas) { Iterator<Integer> i = _bottom.iterator(); int counter = 0; Path path = new Path(); path.moveTo(0, _screen.y); while (i.hasNext()) { path.lineTo(counter, _screen.y-i.next()); counter += _columnWidth; } path.lineTo(_screen.x, _screen.y); path.lineTo(0, _screen.y); canvas.drawPath(path2, _paint); } } The problem is that the game is too 'fast', so I tried with pausing thread with Thread.sleep(50); in run() method of my game thread but then it looks too torn. Well, is there any way to slow down drawing of my terrain ?

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  • High quality/performance shared hosting (in northern Europe)

    - by Bente
    I work as a web developer on almost all levels. However, my typical customer is a 1-5 guys running some sort of consulting business. They have (or want) a web page with some kind of CMS so the can perform most (or all) editing themselves. I normally opt for Concrete5 as my default CMS because it's the most user friendly (and free) CMS I have found. My good recurring customers I host on my own server as a service, but I need a good host for the customers where I want to deliver a product and not be responsible for whatever may happen in the future. However, I still struggle with hosting! Experience shows that the typical ~1$ shared hosting is waaay to slow to run concrete5 smoothly, and a VPS is out of the question because I don't want to maintain it. So, where can I find as fast (from northern Europe), reliable, shared host where I can put a site and don't have to worry about the server going down or being unmaintained. I expect this should cost around $10-$20 but I'm open to all kinds of suggestions because different customers have different budgets.

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  • Automatically keep your local git repos clean

    - by kerry
    Most developers using git are probably aware of a command ‘git gc’ that has to be run from time to time when you notice your git commands are running a little slow. This command cleans up your git repo and makes sure everything is nice and tidy. If you have not run this command lately, you will notice a huge performance increase in your git commands after running. It’s a bit annoying to have to run this command when you notice that your git performance is suffering. The command also takes a while if you have not run it recently. With this in mind, I decided to create a method to automatically run this command from time to time. So I decided to overload cd similar to how rvm does. All you have to do is paste the method in your .profile file and it will run the command every time you enter a directory with a git repo. You’ll notice a little pause when entering the directory, it’s not insufferable but if you would prefer, you can add an & to the end of the command to have it run in the background. I chose the pause over the pid output of the background command. Here it is in all it’s glory. View the code on Gist.

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  • Storing User-uploaded Images

    - by Nyxynyx
    What is the usual practice for handling user uploaded photos and storing them on the database and server? For a user profile image: After receiving the image file from user, rename file to <image_id>_<username> Move image to /images/userprofile Add img filename to a table users containing their profile details like first_name, last_name, age, gender, birthday For a image for a review done by user: After receiving the image file from user, rename file to <image_id>_<review_id> Move image to /images/reviews Add img filename to a table reviews containing their profile details like review_id, review_content, user_id, score. Question 1: How should I go about storing the image filenames if the user can upload multiple photos for a particular review? Serialize? Question 2: Or have another table review_images with columns review_id, image_id, image_filename just for tracking images? Will doing a JOIN when retriving the image_filename from this table slow down performance noticeably? Question 3: Should all the images be stored in a single folder? Will there be a problem when we have 100K photos in the same folder? Is there a more efficient way to go about doing this?

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  • How to implement "bullet time" in a multiplayer game?

    - by Tom
    I have never seen such a feature before, but it should provide an interesting gameplay opportunity. So yes, in a multiplayer/real-time environment (imagine FPS), how could I implement a slow motion/bullet time effect? Something like an illusion for the player that's currently slo-mo'ed. So everybody sees him "real-time", but he sees everything slowed down. Update A sidenote: keep in mind that a FPS game has to be balanced in order for it to be fun. So yes, this bullet time feature has to be solid, giving a small advantage to the "player", while not taking away from other players. Plus, there is a possibility that two players could activate their bullet time at the same time. Furthermore: I'm going to implement this in the future no matter what it takes. And, the idea is to build a whole new game engine for all this. If that gives new options, I'm more then interested in hearing the ideas. Meanwhile, here with my team we're thinking about this too, when our theory will be crafted, I'm going to share it here. Is this even possible? So, the question on "is this even possible" has been answered, now it's time to find the best solution. I'm keeping the "answer" until something exceptionally good comes up, like a prototype theory with something close to working pseudo code.

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  • Disaster Recovery Example

    Previously, I use to work for a small internet company that sells dental plans online. Our primary focus concerning disaster prevention and recovery is on our corporate website and private intranet site. We had a multiphase disaster recovery plan that includes data redundancy, load balancing, and off-site monitoring. Data redundancy is a key aspect of our disaster recovery plan. The first phase of this is to replicate our data to multiple database servers and schedule daily backups of the databases that are stored off site. The next phase is the file replication of data amongst our web servers that are also backed up daily by our collocation. In addition to the files located on the server, files are also stored locally on development machines, and again backed up using version control software. Load balancing is another key aspect of our disaster recovery plan. Load balancing offers many benefits for our system, better performance, load distribution and increased availability. With our servers behind a load balancer our system has the ability to accept multiple requests simultaneously because the load is split between multiple servers. Plus if one server is slow or experiencing a failure the traffic is diverted amongst the other servers connected to the load balancer allowing the server to get back online. The final key to our disaster recovery plan is off-site monitoring that notifies all IT staff of any outages or errors on the main website encountered by the monitor. Messages are sent by email, voicemail, and SMS. According to Disasterrecovery.org, disaster recovery planning is the way companies successfully manage crises with minimal cost and effort and maximum speed compared to others that are forced to make decision out of desperation when disasters occur. In addition Sun Guard stated in 2009 that the first step in disaster recovery planning is to analyze company risks and factor in fixed costs for things like hardware, software, staffing and utilities, as well as indirect costs, such as floor space, power protection, physical and information security, and management. Also availability requirements need to be determined per application and system as well as the strategies for recovery.

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  • Desktop goes un-usable after upgrade to 12.04

    - by Tom Nail
    I have multiple Ubuntu systems connected to a KVM, one of which I recently upgraded from Ubuntu 10 to 12.04. After the upgrade, this system desktop does fine until it is allowed to go to idle (i.e., I've switched to another system on the KVM and it locks it's desktop). When I come back to it, the screen is garbled and paging across at a rate seemingly determined by the mouse. Although no pointer is visible, I can get the screen to stop paging (and just be garbled) by moving the mouse left and right. The paging will slow down and come to a stop, if I can align things carefully enough. This condition persists even when I try to go to a CLI-based login (e.g., CTRL+Alt+F1) and will continue until I reboot the machine. Unfortunately, I'm not very familiar with the Unity desktop, so I don't know where to find things to troubleshoot. A restart of lightdm doesn't change anything, so I'm wondering if this might be more hardware based( although this machine hasn't given me any trouble previously in the same setup). The .xsession-errors file has some issues with compiz, nautilus and GConf listed, but I'm not sure those are actually germane to the issue. Thanks for any help, -=Tom

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  • Companies and Ships

    - by TechnicalWriting
    I have worked for small, medium, large, and extra large companies and they have something in common with ships. These metaphors have been used before, I know, but I will have a go at them.The small company is like a speed boat, exciting and fast, and can turn on a dime, literally. Captain and crew share a lot of the work. A speed boat has a short range and needs to refuel a lot. It has difficulty getting through bad weather. (Small companies often live quarter to quarter. By the way, if a larger company is living quarter to quarter, it is taking on water.)The medium company is is like a battleship. It can maneuver, has a longer range, and the crew is focused on its mission. Its main concern are the other battleships trying to blow it out of the water, but it can respond quickly. Bad weather can jostle it, but it can get through most storms.The large company is like an aircraft carrier; a floating city. It is well-provisioned and can carry a specialized load for a very long range. Because of its size and complexity, it has to be well-organized to be effective and most of its functions are specialized (with little to no functional cross-over). There are many divisions and layers between Captain and crew. It is not very maneuverable; it has to set its course well in advance and have a plan of action.The extra large company is like a cruise liner. It also has to be well-organized and changes in direction are often slow. Some of the people are hard at work behind the scenes to run the ship; others can be along for the ride. They sail the same routes over and over again (often happily) with the occasional cosmetic face-lift to the ship and entertainment. It should stay in warm, friendly waters and avoid risky speed through fields of ice bergs.I have enjoyed my career on the various Ships of Technical Writing, but I get the most of my juice from the battleship where I am closer to the campaign and my contributions have the greater impact on success.Mark Metcalfewww.linkedin.com/in/MarkMetcalfe

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  • Server-side Architecture for Online Game

    - by Draiken
    basically I have a game client that has communicate with a server for almost every action it takes, the game is in Java (using LWJGL) and right now I will start making the server. The base of the game is normally one client communicating with the server alone, but I will require later on for several clients to work together for some functionalities. I've already read how authentication server should be sepparated and I intend on doing it. The problem is I am completely inexperienced in this kind of server-side programming, all I've ever programmed were JSF web applications. I imagine I'll do socket connections for pretty much every game communication since HTML is very slow, but I still don't really know where to start on my server. I would appreciate reading material or guidelines on where to start, what architecture should the game server have and maybe some suggestions on frameworks that could help me getting the client-server communication. I've looked into JNAG but I have no experience with this kind of thing, so I can't really tell if it is a solid and good messaging layer. Any help is appreciated... Thanks ! EDIT: Just a little more information about the game. It is intended to be a very complex game with several functionalities, making some functionalities a "program" inside the program. It is not an usual game, like FPS or RPG but I intend on having a lot of users using these many different "programs" inside the game. If I wasn't clear enough, I'd really appreciate people that have already developed games with java client/server architecture, how they communicated, any frameworks, apis, messaging systems, etc. It is not a question of lack of knowledge of language, more a question for advice, so I don't end up creating something that works, but in the later stages will have to be rewriten for any kind of limiting reason. PS: sorry if my english is not perfect...

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  • Are there any significant advantages to using a native language for mobile app development?

    - by Karl Daniel
    Forgive me if this question has already been answered but I couldn't quite find the answer I was looking for. What I wanted to know was, is there any significant advantage to using a native language when developing and deploying apps to a mobile environment? The reason I ask is for a long while now I've been using Objective-C, Apple's native language for iOS, to build my apps. However I've been wondering whether or not there is any real benefit to doing this, over using a non-native language like JavaScript and then deploying it through a service like 'Phone Gap'? I do stress 'significant' advantages as native languages are always more likely to have the upper hand when it comes to speed and access to the latest APIs. However in general I don't see using a non-native language or a service like 'Phone Gap' causing and major slow down to my apps or restricting my development. Additionally having the ability to deploy to multiple services is also very handy indeed. This is why I put the question, are there any significant advantages to using a native language for mobile app development?

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  • Updating Google sitemap for mobile

    - by dimo414
    I have a series of utilities to generate Google sitemaps for my whole site. These files are massive, and slow to build. We want to start telling Google these pages are mobile-crawl-able too, by adding them to mobile sitemaps, but the documentation is unclear if I need to specify physically different files for my mobile URLs than for my normal ones. If this is my current sitemap: <?xml version="1.0" encoding="UTF-8" ?> <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>http://mobile.example.com/article100.html</loc> </url> </urlset> Can I simply change it to: <?xml version="1.0" encoding="UTF-8" ?> <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:mobile="http://www.google.com/schemas/sitemap-mobile/1.0"> <url> <loc>http://mobile.example.com/article100.html</loc> <mobile:mobile/> </url> </urlset> Or do I need to create new files with the additional markup, alongside my existing files?

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  • Unity in 12.10 comes up behind other windows

    - by ams
    I've just upgraded from 12.04 to 12.10. For the most part, everything works fine, but I have a few small problems with Unity, or maybe Compiz. When I hit the Super key, or click on the dash launcher, the dash sometimes comes up behind the other windows on the screen. As you can imagine, this makes it somewhat tricky to use. Once it has started coming up behind, no amount of trying again will convince it to come back to the front. Possibly related, the Alt-Tab switcher doesn't show either. It maybe that there isn't one, or maybe that's behind also? Alt-Tab does switch the windows, but there's no visual indicator. When I hit Super-W, the windows do all do the zoom thing, but it's slow and juddery where it used to be smooth in 12.04. I'm using the standard "radeon" driver, same as before, with a triple-head monitor setup (and that works fine). I've not tried the proprietary drivers as I've previously found the multi-monitor support much weaker than the default driver, but maybe that's the way to go now? Video play fine. Even WebGL seems ok. Do other see this problem? Is it a bug? Or have I just got some left-over config from 12.04 in the way?

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  • Finding maximum number of congruent numbers

    - by Stefan Czarnecki
    Let's say we have a multiset (set with possible duplicates) of integers. We would like to find the size of the largest subset of the multiset such that all numbers in the subset are congruent to each other modulo some m 1. For example: 1 4 7 7 8 10 for m = 2 the subsets are: (1, 7, 7) and (4, 8, 10), both having size 3. for m = 3 the subsets are: (1, 4, 7, 7, 10) and (8), the larger set of size 5. for m = 4 the subsets are: (1), (4, 8), (7, 7), (10), the largest set of size 2. At this moment it is evident that the best answer is 5 for m = 3. Given m we can find the size of the largest subset in linear time. Because the answer is always equal or larger than half of the size of the set, it is enough to check for values of m upto median of the set. Also I noticed it is necessary to check for only prime values of m. However if values in the set are large the algorithm is still rather slow. Does anyone have any ideas how to improve it?

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  • Faster 2D Collision detection

    - by eShredder
    Recently I've been working on a fast-paced 2d shooter and I came across a mighty problem. Collision detection. Sure, it is working, but it is very slow. My goal is: Have lots of enemies on screen and have them to not touch each other. All of the enemies are chasing the player entity. Most of them have the same speed so sooner or later they all end up taking the same space while chasing the player. This really drops the fun factor since, for the player, it looks like you are being chased by one enemy only. To prevent them to take the same space I added a collision detection (a very basic 2D detection, the only method I know of) which is. Enemy class update method Loop through all enemies (continue; if the loop points at this object) If enemy object intersects with this object Push enemy object away from this enemy object This works fine. As long as I only have <200 enemy entities that is. When I get closer to 300-350 enemy entities my frame rate begins to drop heavily. First I thought it was bad rendering so I removed their draw call. This did not help at all so of course I realised it was the update method. The only heavy part in their update method is this each-enemy-loops-through-every-enemy part. When I get closer to 300 enemies the game does a 90000 (300x300) step itteration. My my~ I'm sure there must be another way to aproach this collision detection. Though I have no idea how. The pages I find is about how to actually do the collision between two objects or how to check collision between an object and a tile. I already know those two things. tl;dr? How do I aproach collision detection between LOTS of entities? Quick edit: If it is to any help, I'm using C# XNA.

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  • When things go awry

    - by Phil Factor
    The moment the Entrepreneur opened his mouth on prime-time national TV, spelled out the URL and waxed big on how exciting ‘his’ new website was, I knew I was in for a busy night. I’d designed and built it. All at once, half a million people tried to log into the website. Although all my stress-testing paid off, I have to admit that the network locked up tight long before there was any danger of a database or website problem. Soon afterwards, the Entrepreneur and the Big Boss were there in the autopsy meeting. We picked through all our systems in detail to see how they’d borne the unexpected strain. Mercifully, in view of the sour mood of the Big Boss, it turned out that the only thing we could have done better was buy a bigger pipe to and from the internet. We’d specified that ‘big pipe’ when designing the system. The Big Boss had then railed at the cost and so we’d subsequently compromised. I felt that my design decisions were vindicated. The Big Boss brooded for a while. Then he made the significant comment: “What really ****** me off is the fact that, for ten minutes, we couldn’t take people’s money.” At that point I stopped feeling smug. Had the internet connection been better, the system would have reached its limit and failed rather precipitously, and that wasn’t what he wanted. Then it occurred to me that what had gummed up the connection was all those images on the site, that had made it so impressive for the visitors. If there had been a way to automatically pare down the site to the bare essentials under stress… Hmm. I began to consider disaster-recovery in the broadest sense – maintaining a service in spite of unusual or unexpected events. What he said makes a lot of sense: sacrifice whatever isn’t essential to keep the core service running when we approach the capacity limits. Maybe in IT we should borrow (or revive) the business concept of the ‘Skeleton service’, maintaining only the priority parts under stress, using a process that is well-prepared and carefully rehearsed. How might this work? Whatever the event we have to prepare for, it is all about understanding the priorities; knowing what one can dispense with when the going gets tough. In the event of database disaster, it’s much faster to deploy a skeletal system with only the essential data than to restore the entire system, though there would have to be a reconciliation process to update the revived database retrospectively, once the emergency was over. It isn’t just the database that could be designed for resilience. One could prepare for unusually high traffic in a website by designing a system that degraded gradually to a ‘skeletal’ site, one that maintained the commercial essentials without fat images, JavaScript libraries and razzmatazz. This is all what the Big Boss scathingly called ‘a mere technicality’. It seems to me that what is needed first is a culture of application and database design which acknowledges that we live in a very imperfect world, and react accordingly when things go awry.

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  • Floating point undesirable in highly critical code?

    - by Kirt Undercoffer
    Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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  • How will closures in Java impact the Java Community?

    - by Ryan Delucchi
    It is one of the most talked about features planned for Java: Closures. Many of us have been longing for them. Some of us (including I) have grown a bit impatient and have turned to scripting languages to fill the void. But, once closures have finally arrived to Java: how will they effect the Java Community? Will the advancement of VM-targetted scripting languages slow to a crawl, stay the same, or acclerate? Will people flock to the new closure syntax, thus turning Java code-bases all-around into more functionally structured implementations? Will we only see closures sprinkled in Java throughout? What will be the effect on tool/IDE support? How about performance? And finally, what will it mean for Java's continued adoption, as a language, compared with other languages that are rising in popularity? To provide an example of one of the latest proposed Java Closure syntax specs: public interface StringOperation { String invoke(String s); } // ... (new StringOperation() { public invoke(String s) { new StringBuilder(s).reverse().toString(); } }).invoke("abcd"); would become ... String reversed = { String s => new StringBuilder(s).reverse().toString() }.invoke("abcd"); [source: http://tronicek.blogspot.com/2007/12/closures-closure-is-form-of-anonymous_28.html]

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  • Architecture : am I doing things right?

    - by Jeremy D
    I'm trying to use a '~classic' layered arch using .NET and Entity Framework. We are starting from a legacy database which is a little bit crappy: Inconsistent naming Unneeded views (view referencing other views, select * views etc...) Aggregated columns Potatoes and Carrots in the same table etc... So I ended with fully isolating my database structure from my domain model. To do so EF entities are hidden from presentation layer. The goal is to permit an easier database refactoring while lowering the impact of it on applications. I'm now facing a lot of challenges and I'm starting to ask myself if I'm doing things right. My Domain Model is highly volatile, it keeps evolving with apps as new fields needs are arising. Complexity of it keeps raising and class it contains start to get a lot of properties. Creating include strategy and reprojecting to EF is very tricky (my domain objects don't have any kind of lazy/eager loading relationship properties): DomainInclude<Domain.Model.Bar>.Include("Customers").Include("Customers.Friends") // To... IFooContext.Bars.Include(...).Include(...).Where(...) Some framework are raping the isolation levels (Devexpress Grids which needs either XPO or IQueryable for filtering and paging large data sets) I'm starting to ask myself if : the isolation of EF auto-generated entities is an unneeded cost. I should allow frameworks to hit IQueryable? Slow slope to hell? (it's really hard to isolate DevExpress framework, any successful experience?) the high volatility of my domain model is normal? Did you have similar difficulties? Any advice based on experience?

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  • Code Clone Analysis on Rawr &ndash; Part 1

    - by Dylan Smith
    In this post we’ll take a look at the first result from the Code Clone Analysis, and do some refactoring to eliminate the duplication.  The first result indicated that it found an exact match repeated 14 times across the solution, with 18 lines of duplicated code in each of the 14 blocks.   Net Lines Of Code Deleted: 179     In this case the code in question was a bunch of classes representing the various Bosses.  Every Boss class has a constructor that initializes a whole bunch of properties of that boss, however, for most bosses a lot of these are simply set to 0’s.     Every Boss class inherits from the class MultiDiffBoss, so I simply moved all the initialization of the various properties to the base class constructor, and left it up to the Boss subclasses to only set those that are different than the default values. In this case there are actually 22 Boss subclasses, however, due to some inconsistencies in the code structure Code Clone only identified 14 of them as identical blocks.  Since I was in there refactoring the 14 identified already, it was pretty straightforward to identify the other 8 subclasses that had the same duplicated behavior and refactor those also.   Note: Code Clone Analysis is pretty slow right now.  It takes approx 1 min to build this solution, but it takes 9 mins to run Code Clone Analysis.  Personally, if the results are high quality I’m OK with it taking a long time to run since I don’t expect it’s something I would be running all that often.  However, it would be nice to be able to run it as part of a nightly build, but at this time I don’t believe it’s possible to run outside of Visual Studio due to a dependency on the meta-data available in the VS environment.

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