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  • Creative Technical Interview Questions for Developers

    - by John Shedletsky
    I do a good number of in-person technical interviews for new developers. I like to ask technical questions where I ask people to either code something up or develop an algorithm to solve a task. I feel my current repertoire is uninspired. In my opinion, the ideal interview question has these qualities: Multiple solutions, where some are obviously better than others, and some that involve subtle trade-offs (discussing tradeoffs is a good way to gauge someone's experience, in my opinion). Novelty - asking the "insert this element into a linked list" question is only good for weeding out people who never did their homework. Elegant - I like questions where the core problem isn't hidden in a lot of details. Everyone should be able to understand the problem, even if everyone can't solve it on the whiteboard. Elegant questions are difficult without involving undue amounts of "domain knowledge" or getting too narrow. Have you been on either side of an interview where someone (maybe you!) asked a particularly good programming or algorithms question?

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  • How to secure an API written in .Net

    - by The Diamond Z
    This is a variation on an existing question in SO about securing/obfuscating .Net applications in general. I'm developing an API in C# that includes some algorithms I'm keen to protect. I understand no method will be perfect, but what's the generally accepted method for doing this? I'd like my clients to be able to code against the API but I don't want them to reverse engineer what's inside (at least I don't want to make it easy for them). If I obfuscate the code, won't that also obfuscate the API? We're looking at smartAssembly any thoughts comments on the product would be appreciated.

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  • How can I make a boring project (another WordPress site) interesting?

    - by Christopher Altman
    WordPress is my example, but the question can be generalized to any technology that is not particularly interesting. To me, WordPress takes away the intellectually gratifying pieces of coding. I would rather write a new version of WordPress than write a WordPress theme and glue together some plugins. I am using WP because my company dictates the platform for some of our clients (I do not disagree with the choice from a business perspective, WP is quick and cheap to implement). My question is, how can I make my next WordPress project interesting? I want to advance my understanding of the fundamentals of programming (aka data structures, algorithms, and caching) but do not see how I can achieve this when coding another WP site. I have a fairly tight understanding of front-end technologies and believe I have made WP do things it was never intended to do. Examples are here and here. Solving front-end related problems is not as interesting as coding a full stack application. Any advice will help.

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  • Latest stream cipher considered reasonably secure & easy to implement?

    - by hythlodayr
    (A)RC4 used to fit the bill, since it was so simple to write. But it's also less-than-secure these days. I'm wondering if there's a successor that's: Code is small enough to write & debug within an hour or so, using pseudo code as a template. Still considered secure, as of 2010. Optimized for software. Not encumbered by licensing issues. I can't use crypto libraries, otherwise all of this would be moot. Also, I'll consider block algorithms though I think most are pretty hefty. Thanks.

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  • "Refreshing" an XML feed on iPhone/Mac OSX

    - by Steve
    Hi all, I'm curious for those of you who are building iPhone apps based on REST/SOAP/XML-RPC or simply pulling down a dynamic XML feed, what does it mean exactly to you when a user says 'refresh' the feed? The straight forward way is to populate some collection, say an NSMutableArray, with whatever you bring down from the feed. If a widget on the UI is available to refresh, I typically do something like: [myMutableArray removeAllObjects]; // follow steps to repopulate myMutableArray It seems this is the least efficient algorithm for refreshing an XML feed. For instance many folks who are building Twitter clients, are appending changes to their existing feed, versus bringing down the entire feed in its complete form again. What kind of algorithms are you using to "refresh" your models when speaking to a server-side data source? Thanks all.

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  • How online-game clients are able to exchange data through internet so fast?

    - by Kirzilla
    Hello, Let's imagine really simple game... We have a labirinth and two players trying to find out exit in real time through internet. On every move game client should send player's coordinates to server and accept current coordinates of another client. How is it possible to make this exchange so fast (as all modern games do). Ok, we can use memcache or similar technology to reduce data mining operations on server side. We can also use fastest webserver etc., but we still will have problems with timings. So, the questions are... What protocol game clients are usually using for exchanging information with server? What server technologies are coming to solve this problem? What algorithms are applied for fighting with delays during game etc. PS: Sorry for my English and I hope that my question is clear. Thank you.

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  • Can you /should you learn SEO techniques

    - by Mark
    I know very little about Search engine optimization however from discussions with other I am now unsure where to start. Are there any books or do these date so quickly that they are obsolete? Do all website give you mis-information or are there any reliable sources? Is it just a case of trial and error and in turn experience? Is it event worth learning the techniques as search engines change their algorithms so regularly? I wonder if it just better to spend the time to ensure you have a regularly updated will written web site with quality content, site map, quality links etc..

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  • Artificial Intelligence Project - What language should I go for?

    - by Kremlin Yocepf
    Hi, I am a computer science student and I am going to work on an artificial intelligence project which will compose a musical tune according to the genre and mood inputs. Are the algorithms to be used for this project likely to be very resource-consuming? Would it make any difference (in terms of speed) if I choose to go with Java rather than C++? (Note : I know only these two languages and I am more comfortable with Java than C++.) NB : Sorry for my poor English. If someone can, please clean up this post wherever necessary. Thanks.

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  • Is there a circular hash function?

    - by Phil H
    Thinking about this question on testing string rotation, I wondered: Is there was such thing as a circular/cyclic hash function? E.g. h(abcdef) = h(bcdefa) = h(cdefab) etc Uses for this include scalable algorithms which can check n strings against each other to see where some are rotations of others. I suppose the essence of the hash is to extract information which is order-specific but not position-specific. Maybe something that finds a deterministic 'first position', rotates to it and hashes the result? It all seems plausible, but slightly beyond my grasp at the moment; it must be out there already...

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  • Display (tier) prices with qty increments and taxes

    - by witrin
    I need to display (tier) prices based on the qty increments of a product. E.g. a simple product, with a regular price of 50¢, no taxes and qty increments of 20 should be displayed on product views with "$10 per 20". Without using taxes this should be quite easy. But there seems to be no "default" helper or model to do this with taxes enabled and different calulation algorithms (e.g. Mage_Tax_Model_Calculation::CALC_UNIT_BASE); expect for quotes in Mage_Tax_Model_Sales_Total_Quote_Tax and Mage_Tax_Model_Sales_Total_Quote_Subtotal. Did I miss something here, or do I have to write the business logic on my own? And how I would best encapsulate it?

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  • SQL SERVER – When are Statistics Updated – What triggers Statistics to Update

    - by pinaldave
    If you are an SQL Server Consultant/Trainer involved with Performance Tuning and Query Optimization, I am sure you have faced the following questions many times. When is statistics updated? What is the interval of Statistics update? What is the algorithm behind update statistics? These are the puzzling questions and more. I searched the Internet as well many official MS documents in order to find answers. All of them have provided almost similar algorithm. However, at many places, I have seen a bit of variation in algorithm as well. I have finally compiled the list of various algorithms and decided to share what was the most common “factor” in all of them. I would like to ask for your suggestions as whether following the details, when Statistics is updated, are accurate or not. I will update this blog post with accurate information after receiving your ideas. The answer I have found here is when statistics are expired and not when they are automatically updated. I need your help here to answer when they are updated. Permanent table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in a table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Temporary table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in table is less than 6, statistics is updated for every 6 changes in table. If the number of rows in table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Table variable There is no statistics for Table Variables. If you want to read further about statistics, I suggest that you read the white paper Statistics Used by the Query Optimizer in Microsoft SQL Server 2008. Let me know your opinions about statistics, as well as if there is any update in the above algorithm. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Question, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Statistics

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  • Effectively implementing a game view using java

    - by kdavis8
    I am writing a 2d game in java. The game mechanics are similar to the Pokémon game boy advance series e.g. fire red, ruby, diamond and so on. I need a way to draw a huge map maybe 5000 by 5000 pixels and then load individual in game sprites to across the entirety of the map, like rendering a scene. Game sprites would be things like terrain objects, trees, rocks, bushes, also houses, castles, NPC's and so on. But i also need to implement some kind of camera view class that focuses on the player. the camera view class needs to follow the characters movements throughout the game map but it also needs to clip the rest of the map away from the user's field of view, so that the user can only see the arbitrary proximity adjacent to the player's sprite. The proximity's range could be something like 500 pixels in every direction around the player’s sprite. On top of this, i need to implement an independent resolution for the game world so that the game view will be uniform on all screen sizes and screen resolutions. I know that this does sound like a handful and may fall under the category of multiple questions, but the questions are all related and any advice would be very much appreciated. I don’t need a full source code listing but maybe some pointers to effective java API classes that could make doing what i need to do a lot simpler. Also any algorithmic/ design advice would greatly benefit me as well. example of what i am trying to do in source code form below package myPackage; /** * The Purpose of GameView is to: Render a scene using Scene class, Create a * clipping pane using CameraView class, and finally instantiate a coordinate * grid using Path class. * * Once all of these things have been done, GameView class should then be * instantiated and used jointly with its helper classes. CameraView should be * used as the main drawing image. CameraView is the the window to the game * world.Scene passes data constantly to CameraView so that the entire map flows * smoothly. Path uses the x and y coordinates from camera view to construct * cells for path finding algorithms. */ public class GameView { // Scene is a helper class to game view. it renders the entire map to memory // for the camera view. Scene scene; // Camera View is a helper class to game view. It clips the Scene into a // small image that follows the players coordinates. CameraView Camera; // Path is a helper class to game view. It observes and calculates the // coordinates of camera view and divides them into Grids/Cells for Path // finding. Path path; // this represents the player and has a getSprite() method that will return // the current frame column row combination of the passed sprite sheet. Sprite player; }

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  • NHibernate 2 Beginner's Guide Review

    - by Ricardo Peres
    OK, here's the review I promised a while ago. This is a beginner's introduction to NHibernate, so if you have already some experience with NHibernate, you will notice it lacks a lot of concepts and information. It starts with a good description of NHibernate and why would we use it. It goes on describing basic mapping scenarios having primary keys generated with the HiLo or Identity algorithms, without actually explaining why would we choose one over the other. As for mapping, the book talks about XML mappings and provides a simple example of Fluent NHibernate, comparing it to its XML counterpart. When it comes to relations, it covers one-to-many/many-to-one and many-to-many, not one-to-one relations, but only talks briefly about lazy loading, which is, IMO, an important concept. Only Bags are described, not any of the other collection types. The log4net configuration description gets it's own chapter, which I find excessive. The chapter on configuration merely lists the most common properties for configuring NHibernate, both in XML and in code. Querying only talks about loading by ID (using Get, not Load) and using Criteria API, on which a paging example is presented as well as some common filtering options (property equals/like/between to, no examples on conjunction/disjunction, however). There's a chapter fully dedicated to ASP.NET, which explains how we can use NHibernate in web applications. It basically talks about ASP.NET concepts, though. Following it, another chapter explains how we can build our own ASP.NET providers using NHibernate (Membership, Role). The available entity generators for NHibernate are referred and evaluated on a chapter of their own, the list is fine (CodeSmith, nhib-gen, AjGenesis, Visual NHibernate, MyGeneration, NGen, NHModeler, Microsoft T4 (?) and hbm2net), examples are provided whenever possible, however, I have some problems with some of the evaluations: for example, Visual NHibernate scores 5 out of 5 on Visual Studio integration, which simply does not exist! I suspect the author means to say that it can be launched from inside Visual Studio, but then, what can't? Finally, there's a chapter I really don't understand. It seems like a bag where a lot of things are thrown in, like NHibernate Burrow (which actually isn't explained at all), Blog.Net components, CSS template conversion and web.config settings related to the maximum request length for file uploads and ending with XML configuration, with the help of GhostDoc. Like I said, the book is only good for absolute beginners, it does a fair job in explaining the very basics, but lack a lot of not-so-basic concepts. Among other things, it lacks: Inheritance mapping strategies (table per class hierarchy, table per class, table per concrete class) Load versus Get usage Other usefull ISession methods First level cache (Identity Map pattern) Other collection types other that Bag (Set, List, Map, IdBag, etc Fetch options User Types Filters Named queries LINQ examples HQL examples And that's it! I hope you find this review useful. The link to the book site is https://www.packtpub.com/nhibernate-2-x-beginners-guide/book

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  • Resources such as libraries, engines and frameworks to make Javacript-based MMORTS? [closed]

    - by hhh
    I am looking for resources outlined to make a MMORTS with Javascript as the client-side, probably just a simple canvas for the frontend. The guy in the video here mentions that JavaScript is one of the most misunderstood language -- and I do believe that. I think one can make quite cool games with it in the future. So I am now proactively looking for resources and perhaps some ideas. My first idea contained Node.js, C and NetBSD/bozohttpd (or the-4-7-chars' *ix-thing with green-logo -thing, move the q here) but I acknowledge my beginner -style approach -- this issue is broad and not only for one person to make it all-the-time-improved project! So I think perfect for community to tinker. Some games and examples possibly easy to make into MMORTS BrowserQuest here under MPL 2.0 and its content licensed under CC-BY-SA 3.0 (source here) [proprietary] LoU here and built with JS/Qooxdoo/c#/Windows-Server/ISS/etc, source. MY ANSWER BEGINS HERE TO BE MOVED BELOW, REQUIRING RE-OPENING. PLEASE, VOTE TO OPEN IT -- HELP US TO TINKER! My answer Generic Is there an MMO-related research body? Although about Android, certain things also appropriate with JS -game: Are there any 2D gaming libraries/frameworks/engines for Android? Why is it so hard to develop a MMO? Browser based MMO Architecture MMO architecture - Highly Scalable with Reporting capabilities What are the Elements of an MMO Game? Is this the right architecture for our MMORPG mobile game? Looking for architectures to develop massive multiplayer game server Information on seamless MMO server architecture Game-mechanics (search) Question sounding like about LoU: What are the different ways to balance an online multiplayer game where user spend different amounts of time online? Building an instance system What are the different ways to balance an online multiplayer game where user spend different amounts of time online? Hosting is it possible to make a MMO starting with scalable hosting? Should I keep login server apart from game server? MMO techniques, algorithms and resources for keeping bandwidth low? MMO Proxy Server Javascript and Client-based things What do I need to do a MMORTS in JavaScript with small amount of Developers? How to update the monsters in my MMO server using Node.js and Socket.IO Are there any good html 5 mmo design tutorials? Networking Loadbalancing Questions Something about TCP, routers, NAT, etc: How do I start writing an MMO game server? Who does the AI calculations in an MMO? They need someone more knowledgable to work with, a lot of cases where the same words mean different things. Data Structures What data structure should I use for a Diablo/WoW-style talent tree? Game Engine Need an engine for MMO mockup Helper sites http://www.gamedev.net/page/index.html

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  • SQL SERVER – ColumnStore Index – Batch Mode vs Row Mode

    - by pinaldave
    What do you do when you are in a hurry and hear someone say things which you do not agree or is wrong? Well, let me tell you what I do or what I recently did. I was walking by and heard someone mentioning “Columnstore Index are really great as they are using Batch Mode which makes them seriously fast.” While I was passing by and I heard this statement my first reaction was I thought Columnstore Index can use both – Batch Mode and Row Mode. I stopped by even though I was in a hurry and asked the person if he meant that Columnstore indexes are seriously fast because they use Batch Mode all the time or Batch Mode is one of the reasons for Columnstore Index to be faster. He responded that Columnstore Indexes can run only in Batch Mode. However, I do not like to confront anybody without hearing their complete story. Honestly, I like to do information sharing and avoid confronting as much as possible. There are always ways to communicate the same positively. Well, this is what I did, I quickly pull up my earlier article on Columnstore Index and copied the script to SQL Server Management Studio. I created two versions of the script. 1) Very Large Table 2) Reasonably Small Table. I a query which uses columnstore index on both of the versions. I found very interesting result of the my tests. I saved my tests and sent it to the person who mentioned about that Columnstore Indexes are using Batch Mode only. He immediately acknowledged that indeed he was incorrect in saying that Columnstore Index uses only Batch Mode. What really caught my attention is that he also thanked me for sending him detail email instead of just having argument where he and I both were standing in the corridor and neither have no way to prove any theory. Here is the screenshots of the both the scenarios. 1) Columnstore Index using Batch Mode 2) Columnstore Index using Row Mode Here is the logic behind when Columnstore Index uses Batch Mode and when it uses Row Mode. A batch typically represents about 1000 rows of data. Batch mode processing also uses algorithms that are optimized for the multicore CPUs and increased memory throughput.  Batch mode processing spreads metadata access costs and overhead over all the rows in a batch.  Batch mode processing operates on compressed data when possible leading superior performance. Here is one last point – Columnstore Index can use Batch Mode or Row Mode but Batch Mode processing is only available in Columnstore Index. I hope this statement truly sums up the whole concept. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Index, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Open Source but not Free Software (or vice versa)

    - by TRiG
    The definition of "Free Software" from the Free Software Foundation: “Free software” is a matter of liberty, not price. To understand the concept, you should think of “free” as in “free speech,” not as in “free beer.” Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it means that the program's users have the four essential freedoms: The freedom to run the program, for any purpose (freedom 0). The freedom to study how the program works, and change it to make it do what you wish (freedom 1). Access to the source code is a precondition for this. The freedom to redistribute copies so you can help your neighbor (freedom 2). The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this. A program is free software if users have all of these freedoms. Thus, you should be free to redistribute copies, either with or without modifications, either gratis or charging a fee for distribution, to anyone anywhere. Being free to do these things means (among other things) that you do not have to ask or pay for permission to do so. The definition of "Open Source Software" from the Open Source Initiative: Open source doesn't just mean access to the source code. The distribution terms of open-source software must comply with the following criteria: Free Redistribution The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale. Source Code The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed. Derived Works The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software. Integrity of The Author's Source Code The license may restrict source-code from being distributed in modified form only if the license allows the distribution of "patch files" with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software. No Discrimination Against Persons or Groups The license must not discriminate against any person or group of persons. No Discrimination Against Fields of Endeavor The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research. Distribution of License The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties. License Must Not Be Specific to a Product The rights attached to the program must not depend on the program's being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program's license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution. License Must Not Restrict Other Software The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software. License Must Be Technology-Neutral No provision of the license may be predicated on any individual technology or style of interface. These definitions, although they derive from very different ideologies, are broadly compatible, and most Free Software is also Open Source Software and vice versa. I believe, however, that it is possible for this not to be the case: It is possible for software to be Open Source without being Free, or to be Free without being Open Source. Questions Is my belief correct? Is it possible for software to fall into one camp and not the other? Does any such software actually exist? Please give examples. Clarification I've already accepted an answer now, but I seem to have confused a lot of people, so perhaps a clarification is in order. I was not asking about the difference between copyleft (or "viral", though I don't like that term) and non-copyleft ("permissive") licenses. Nor was I asking about your personal idiosyncratic definitions of "Free" and "Open". I was asking about "Free Software as defined by the FSF" and "Open Source Software as defined by the OSI". Are the two always the same? Is it possible to be one without being the other? And the answer, it seems, is that it's impossible to be Free without being Open, but possible to be Open without being Free. Thank you everyone who actually answered the question.

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  • Fair Comments

    - by Tony Davis
    To what extent is good code self-documenting? In one of the most entertaining sessions I saw at the recent PASS summit, Jeremiah Peschka (blog | twitter) got a laugh out of a sleepy post-lunch audience with the following remark: "Some developers say good code is self-documenting; I say, get off my team" I silently applauded the sentiment. It's not that all comments are useful, but that I mistrust the basic premise that "my code is so clearly written, it doesn't need any comments". I've read many pieces describing the road to self-documenting code, and my problem with most of them is that they feed the myth that comments in code are a sign of weakness. They aren't; in fact, used correctly I'd say they are essential. Regardless of how far intelligent naming can get you in describing what the code does, or how well any accompanying unit tests can explain to your fellow developers why it works that way, it's no excuse not to document fully the public interfaces to your code. Maybe I just mixed with the wrong crowd while learning my favorite language, but when I open a stored procedure I lose the will even to read it unless I see a big Phil Factor- or Jeff Moden-style header summarizing in plain English what the code does, how it fits in to the broader application, and a usage example. This public interface describes the high-level process and should explain the role of the code, clearly, for fellow developers, language non-experts, and even any non-technical stake holders in the project. When you step into the body of the code, the low-level details, then I agree that the rules are somewhat different; especially when code is subject to frequent refactoring that can quickly render comments redundant or misleading. At their worst, here, inline comments are sticking plaster to cover up the scars caused by poor naming conventions, failure in clarity when mapping a complex domain into code, or just by not entirely understanding the problem (/ this is the clever part). If you design and refactor your code carefully so that it is as simple as possible, your functions do one thing only, you avoid having two completely different algorithms in the same piece of code, and your functions, classes and variables are intelligently named, then, yes, the need for inline comments should be minimal. And yet, even given this, I'd still argue that many languages (T-SQL certainly being one) just don't lend themselves to readability when performing even moderately-complex tasks. If the algorithm is complex, I still like to see the occasional helpful comment. Please, therefore, be as liberal as you see fit in the detail of the comments you apply to this editorial, for like code it is bound to increase its' clarity and usefulness. Cheers, Tony.

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  • Giving a Bomberman AI intelligent bomb placement

    - by Paul Manta
    I'm trying to implement an AI algorithm for Bomberman. Currently I have a working but not very smart rudimentary implementation (the current AI is overzealous in placing bombs). This is the first AI I've ever tried implementing and I'm a bit stuck. The more sophisticated algorithms I have in mind (the ones that I expect to make better decisions) are too convoluted to be good solutions. What general tips do you have for implementing a Bomberman AI? Are there radically different approaches for making the bot either more defensive or offensive? Edit: Current algorithm My current algorithm goes something like this (pseudo-code): 1) Try to place a bomb and then find a cell that is safe from all the bombs, including the one that you just placed. To find that cell, iterate over the four directions; if you can find any safe divergent cell and reach it in time (eg. if the direction is up or down, look for a cell that is found to the left or right of this path), then it's safe to place a bomb and move in that direction. 2) If you can't find and safe divergent cells, try NOT placing a bomb and look again. This time you'll only need to look for a safe cell in only one direction (you don't have to diverge from it). 3) If you still can't find a safe cell, don't do anything. for $(direction) in (up, down, left, right): place bomb at current location if (can find and reach divergent safe cell in current $(direction)): bomb = true move = $(direction) return for $(direction) in (up, down, left, right): do not place bomb at current location if (any safe cell in the current $(direction)): bomb = false move = $(direction) return else: bomb = false move = stay_put This algorithm makes the bot very trigger-happy (it'll place bombs very frequently). It doesn't kill itself, but it does have a habit of making itself vulnerable by going into dead ends where it can be blocked and killed by the other players. Do you have any suggestions on how I might improve this algorithm? Or maybe I should try something completely different? One of the problems with this algorithm is that it tends to leave the bot with very few (frequently just one) safe cells on which it can stand. This is because the bot leaves a trail of bombs behind it, as long as it doesn't kill itself. However, leaving a trail of bombs behind leaves few places where you can hide. If one of the other players or bots decide to place a bomb somewhere near you, it often happens that you have no place to hide and you die. I need a better way to decide when to place bombs.

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  • A* navigational mesh path finding

    - by theguywholikeslinux
    So I've been making this top down 2D java game in this framework called Greenfoot [1] and I've been working on the AI for the guys you are gonna fight. I want them to be able to move around the world realistically so I soon realized, amongst a couple of other things, I would need some kind of pathfinding. I have made two A* prototypes. One is grid based and then I made one that works with waypoints so now I need to work out a way to get from a 2d "map" of the obstacles/buildings to a graph of nodes that I can make a path from. The actual pathfinding seems fine, just my open and closed lists could use a more efficient data structure, but I'll get to that if and when I need to. I intend to use a navigational mesh for all the reasons out lined in this post on ai-blog.net [2]. However, the problem I have faced is that what A* thinks is the shortest path from the polygon centres/edges is not necessarily the shortest path if you travel through any part of the node. To get a better idea you can see the question I asked on stackoverflow [3]. I got a good answer concerning a visibility graph. I have since purchased the book (Computational Geometry: Algorithms and Applications [4]) and read further into the topic, however I am still in favour of a navigational mesh (See "Managing Complexity" [5] from Amit’s Notes about Path-Finding [6]). (As a side note, maybe I could possibly use Theta* to convert multiple waypoints into one straight line if the first and last are not obscured. Or each time I move back check to the waypoint before last to see if I can go straight from that to this) So basically what I want is a navigational mesh where once I have put it through a funnel algorithm (e.g. this one from Digesting Duck [7]) I will get the true shortest path, rather than get one that is the shortest path following node to node only, but not the actual shortest given that you can go through some polygons and skip nodes/edges. Oh and I also want to know how you suggest storing the information concerning the polygons. For the waypoint prototype example I made I just had each node as an object and stored a list of all the other nodes you could travel to from that node, I'm guessing that won't work with polygons? and how to I tell if a polygon is open/traversable or if it is a solid object? How do I store which nodes make up the polygon? Finally, for the record: I do want to programme this by myself from scratch even though there are already other solutions available and I don't intend to be (re) using this code in anything other than this game so it does not matter that it will inevitably be poor quality. http://greenfoot.org http://www.ai-blog.net/archives/000152.html http://stackoverflow.com/q/7585515/ http://www.cs.uu.nl/geobook/ http://theory.stanford.edu/~amitp/GameProgramming/MapRepresentations.html http://theory.stanford.edu/~amitp/GameProgramming/ http://digestingduck.blogspot.com/2010/03/simple-stupid-funnel-algorithm.html

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  • SQL SERVER – Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical functions FIRST_VALUE() and LAST_VALUE(). This function returns first and last value from the list. It will be very difficult to explain this in words so I’d like to attempt to explain its function through a brief example. Instead of creating a new table, I will be using the AdventureWorks sample database as most developers use that for experiment purposes. Now let’s have fun following query: USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: What’s the most interesting thing here is that as we go from row 1 to row 10, the value of the FIRST_VALUE() remains the same but the value of the LAST_VALUE is increasing. The reason behind this is that as we progress in every line – considering that line and all the other lines before it, the last value will be of the row where we are currently looking at. To fully understand this statement, see the following figure: This may be useful in some cases; but not always. However, when we use the same thing with PARTITION BY, the same query starts showing the result which can be easily used in analytical algorithms and needs. Let us have fun through the following query: Let us fun following query. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: Let us understand how PARTITION BY windows the resultset. I have used PARTITION BY SalesOrderID in my query. This will create small windows of the resultset from the original resultset and will follow the logic or FIRST_VALUE and LAST_VALUE in this resultset. Well, this is just an introduction to these functions. In the future blog posts we will go deeper to discuss the usage of these two functions. By the way, these functions can be applied over VARCHAR fields as well and are not limited to the numeric field only. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • More details on America's Cup use of Oracle Data Mining

    - by charlie.berger
    BMW Oracle Racing's America's Cup: A Victory for Database Technology BMW Oracle Racing's victory in the 33rd America's Cup yacht race in February showcased the crew's extraordinary sailing expertise. But to hear them talk, the real stars weren't actually human. "The story of this race is in the technology," says Ian Burns, design coordinator for BMW Oracle Racing. Gathering and Mining Sailing DataFrom the drag-resistant hull to its 23-story wing sail, the BMW Oracle USA trimaran is a technological marvel. But to learn to sail it well, the crew needed to review enormous amounts of reliable data every time they took the boat for a test run. Burns and his team collected performance data from 250 sensors throughout the trimaran at the rate of 10 times per second. An hour of sailing alone generates 90 million data points.BMW Oracle Racing turned to Oracle Data Mining in Oracle Database 11g to extract maximum value from the data. Burns and his team reviewed and shared raw data with crew members daily using a Web application built in Oracle Application Express (Oracle APEX). "Someone would say, 'Wouldn't it be great if we could look at some new combination of numbers?' We could quickly build an Oracle Application Express application and share the information during the same meeting," says Burns. Analyzing Wind and Other Environmental ConditionsBurns then streamed the data to the Oracle Austin Data Center, where a dedicated team tackled deeper analysis. Because the data was collected in an Oracle Database, the Data Center team could dive straight into the analytics problems without having to do any extract, transform, and load processes or data conversion. And the many advanced data mining algorithms in Oracle Data Mining allowed the analytics team to build vital performance analytics. For example, the technology team could remove masking elements such as environmental conditions to give accurate data on the best mast rotation for certain wind conditions. Without the data mining, Burns says the boat wouldn't have run as fast. "The design of the boat was important, but once you've got it designed, the whole race is down to how the guys can use it," he says. "With Oracle database technology we could compare the incremental improvements in our performance from the first day of sailing to the very last day. With data mining we could check data against the things we saw, and we could find things that weren't otherwise easily observable and findable."

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  • Voxel Face Crawling (Mesh simplification, possibly using greedy)

    - by Tim Winter
    This is in regards to a Minecraft-like terrain engine. I store blocks in chunks (16x256x16 blocks in a chunk). When I generate a chunk, I use multiple procedural techniques to set the terrain and to place objects. While generating, I keep one 1D array for the full chunk (solid or not) and a separate 1D array of solid blocks. After generation, I iterate through the solid blocks checking their neighbors so I only generate block faces that don't have solid neighbors. I store which faces to generate in their own list (that's 6 lists, one per possible face). When rendering a chunk, I render all lists in the camera's current chunk and only the lists facing the camera in all other chunks. Using a 2D atlas with this little shader trick Andrew Russell suggested, I want to merge similar faces together completely. That is, if they are in the same list (same normal), are adjacent to each other, have the same light level, etc. My assumption would be to have each of the 6 lists sorted by the axis they rest on, then by the other two axes (the list for the top of a block would be sorted by it's Y value, then X, then Z). With this alone, I could quite easily merge strips of faces, but I'm looking to merge more than just strips together when possible. I've read up on this greedy meshing algorithm, but I am having a lot of trouble understanding it. To even use it, I would think I'd need to perform a type of flood-fill per sorted list to get the groups of merge-able faces. Then, per group, perform the greedy algorithm. It all sounds awfully expensive if I would ever want dynamic terrain/lighting after initial generation. So, my question: To perform merging of faces as described (ignoring whether it's a bad idea for dynamic terrain/lighting), is there perhaps an algorithm that is simpler to implement? I would also quite happily accept an answer that walks me through the greedy algorithm in a much simpler way (a link or explanation). I don't mind a slight performance decrease if it's easier to implement or even if it's only a little better than just doing strips. I worry that most algorithms focus on triangles rather than quads and using a 2D atlas the way I am, I don't know that I could implement something triangle based with my current skills. PS: I already frustum cull per chunk and as described, I also cull faces between solid blocks. I don't occlusion cull yet and may never.

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  • Is the science of Computer Science dead?

    - by Veaviticus
    Question : Is the science and art of CS dead? By that I mean, the real requirements to think, plan and efficiently solve problems seems to be falling away from CS these days. The field seems to be lowering the entry-barrier so more people can 'program' without having to learn how to truly program. Background : I'm a recent graduate with a BS in Computer Science. I'm working a starting position at a decent sized company in the IT department. I mostly do .NET and other Microsoft technologies at my job, but before this I've done Java stuff through internships and the like. I personally am a C++ programmer for my own for-fun projects. In Depth : Through the work I've been doing, it seems to me that the intense disciplines of a real science don't exist in CS anymore. In the past, programmers had to solve problems efficiently in order for systems to be robust and quick. But now, with the prevailing technologies like .NET, Java and scripting languages, it seems like efficiency and robustness have been traded for ease of development. Most of the colleagues that I work with don't even have degrees in Computer Science. Most graduated with Electrical Engineering degrees, a few with Software Engineering, even some who came from tech schools without a 4 year program. Yet they get by just fine without having the technical background of CS, without having studied theories and algorithms, without having any regard for making an elegant solution (they just go for the easiest, cheapest solution). The company pushes us to use Microsoft technologies, which take all the real thought out of the matter and replace it with libraries and tools that can auto-build your project for you half the time. I'm not trying to hate on the languages, I understand that they serve a purpose and do it well, but when your employees don't know how a hash-table works, and use the wrong sorting methods, or run SQL commands that are horribly inefficient (but get the job done in an acceptable time), it feels like more effort is being put into developing technologies that coddle new 'programmers' rather than actually teaching people how to do things right. I am interested in making efficient and, in my opinion, beautiful programs. If there is a better way to do it, I'd rather go back and refactor it than let it slide. But in the corporate world, they push me to complete tasks quickly rather than elegantly. And that really bugs me. Is this what I'm going to be looking forward to the rest of my life? Are there still positions out there for people who love the science and art of CS rather than just the paycheck? And on the same note, here's a good read if you haven't seen it before The Perils Of Java Schools

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  • Language Club

    - by Ben Griswold
    We started a language club at work this week.  Thus far, we have a collective interest in a number of languages: Python, Ruby, F#, Erlang, Objective-C, Scala, Clojure, Haskell and Go. There are more but these 9 received the most votes. During the first few meetings we are going to determine which language we should tackle first. To help make our selection, each member will provide a quick overview of their favored language by answering the following set of questions: Why are you interested in learning “your” language(s). (There’s lots of work, I’m an MS shill, It’s hip and  fun, etc) What type of language is it?  (OO, dynamic, functional, procedural, declarative, etc) What types of problems is your language best suited to solve?  (Algorithms over big data, rapid application development, modeling, merely academic, etc) Can you provide examples of where/how it is being used?  If it isn’t being used, why not?  (Erlang was invented at Ericsson to provide an extremely fault tolerant, concurrent system.) Quick history – Who created/sponsored the language?  When was it created?  Is it currently active? Does the language have hardware support (an attempt was made at one point to create processor instruction sets specific to Prolog), or can it run as an interpreted language inside another language (like Ruby in the JVM)? Are there facilities for programs written in this language to communicate with other languages?  How does this affect its utility? Does the language have a IDE tool support?  (Think Eclipse or Visual Studio) How well is the language supported in terms of books, community and documentation? What’s the number one things which differentiates the language from others?  (i.e. Why is it cool?) How is the language applicability to us as consultants?  What would the impact be of using the language in terms of cost, maintainability, personnel costs, etc.? What’s the number one things which differentiates the language from others?  (i.e. Why is it cool?) This should provide an decent introduction into nearly a dozen languages and give us enough context to decide which single language deserves our undivided attention for the weeks to come.  Stay tuned for the winner…

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  • JavaScript in different browsers

    - by PointsToShare
    Adventures with JavaScript rendered in IE 8, Chrome 15, and Firefox 8.0 I have written a little monogram about the advantages of Math and wrote a few JavaScript applications to demonstrate them. I was a bit careless and used elements on the page in my JavaScript without using any of the GetElementsByXXXX methods to identify them.  Say I had a text box named tbSeqNum into which I entered a number to be used in a computation. In my code I simply referred to its value by using it directly. Like here: Function Blah() {                 return tbSeqNum.value; } This ran fine in IE8. In IE, the elements are available as global variables. This is not the case in either Firefox or Chrome. In there one has to create the variable and only then use it. Assuming I also used tbSeqNum as the element’s ID, this works: Function Blah() {                 return GetElementById(“tbSeqNum”).value; } Naturally this corrected function also works in IE, so be warned. Also, coming from windows programming (I am long in the tooth and programmed long before the internet), I have a habit of putting an “Exit” button on my pages and setting their onclick to: onclick=”window.close()”. Again, this works fine in IE. In Firefox and chrome, it does not! There you can only close a window that you opened in the code. A window that was opened by navigation to a URL will not close.  Before I deployed mu code to my website, I painfully removed all my Exit buttons. But my greatest surprise came when I tested my pages in the various browsers. In my code I do a comparison on the performance of two algorithms used to solve the same problem. One is brute force, the other uses a mathematical formula. The compare functions runs each many times and displays the time it took for each and also the ratio. Chrome runs JavaScript between 5 and 10 times faster than Firefox and between 50 and 100 times faster that IE. Wow!!! This difference is especially remarkable when the code uses iteration. I suspect that the JS engines in Chrome and Firefox simply cache the result of a function and if it is called again with the same parameters, it returns the cached result. To see it in action play run the “How Many Squares” page in www.mgsltns.com/games.htm The host is running on Unix, so the link is case sensitive. Last Note: IE9 runs JS a bit faster, but still lags behind almost as badly. That’s All Folks!

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