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  • Caching strategies - LRU, MRU, Clock-Pro

    - by golgofa
    I am going to write a bachelor's science work on caching strategies and really, can't find any links to specifications or full descriptions of some of them. Only something like summaries from wikipedia. Please, help with some links on LRU, MRU caching and new-one - Clock Pro. Thanks a lot. All links are very useful for me. The purpose of work - is to compare different cache strategies to get more effiency. It based on WebApplication with ejb 2.0, so algorithm's will be implemented there, espesially in ejbLoad() and ejbFindByPrimarKey(). Also, one of aspects of this application - it will use not common scheme of tables in database - it based on metamodel. So, if you had any experience on this topic, i would be grateful to take some of your knowledge)

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  • How to create realistic 2d lighting using colour temperature

    - by Truncheon
    I'm looking for a lighting algorithm that produces realistic lights expressed in kelvins, from about 2500k to 6500k. What I'm confused about is how to make the lights properly interact with the colors of game objects. If a whole level is fully lit (overcast daylight) then it would seem that I should use just the color of the object. But what if I'm in a closed room with no windows, and there is an incandescent bulb shining light in the room? How would that light properly light up the objects in the room? There does not seem to be an obvious solution to the problem. And simply mixing the color of the light with the colors of the object, seems an inaccurate approach.

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  • Tips for building an AI for a 2D racing game

    - by declique
    I have a school project to build an AI for a 2D racing game in which it will compete with several other AIs (no collision). We are given a black and white bitmap image of the racing track, we are allowed to choose basic stats for our car (handling, acceleration, max speed and brakes) after we receive the map. The AI connects to the game's server and gives to it several times a second numbers for the current acceleration and steering. The language I chose is C++, by the way. The questions are: What is the best strategy or algorithm (since I want to try and win)? I currently have in mind some ideas found on the net and one or two of my own, but I would like before I start to code that my perspective is one of the best. What good books are there on that matter? What sites should I refer to?

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  • Redirect from the main page on multilanguage site

    - by Pluto
    I've decided to start developing multilingual web site. Now I'm thinking about the structure. The idea is to use a simple algorithm to find out what language is most interesting to the visitor when he makes his first visit to the root page, and then forward him to the corresponding address, for example, http://example.com/en/ for English-speaking audience and http://example.com/ru/ for Russians. The question is, how search engines react on such redirect? If this approach does not take away site's reputation, which redirects should I choose: 301 or 302? I would be very grateful for the reasoned response.

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  • Is acousting fingerprinting too broad for one audio file only?

    - by IBG
    So we were looking for some topics related to audio analysis and found acoustic fingerprinting. As it is, it seems like the most famous application for it is for identification of music. Enter our manager, who requested us to research and possible find an algorithm or existing code that we can use for this very simple approach (like it's easy, source codes don't show up like mushrooms): Always-on app for listening Compare the audio patterns to a single audio file (assume sound is a simple beep) If beep is detected, send notification to server With a flow this simple, do you think acousting fingerprinting is a broad approach to use? Should we stop and take another approach? Where to best start? We haven't started anything yet (on the development side) on this regard, so I want to get other opinion if this is pursuit is worth it or moot.

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  • How to document and teach others "optimized beyond recognition" computationally intensive code?

    - by rwong
    Occasionally there is the 1% of code that is computationally intensive enough that needs the heaviest kind of low-level optimization. Examples are video processing, image processing, and all kinds of signal processing, in general. The goals are to document, and to teach the optimization techniques, so that the code does not become unmaintainable and prone to removal by newer developers. (*) (*) Notwithstanding the possibility that the particular optimization is completely useless in some unforeseeable future CPUs, such that the code will be deleted anyway. Considering that software offerings (commercial or open-source) retain their competitive advantage by having the fastest code and making use of the newest CPU architecture, software writers often need to tweak their code to make it run faster while getting the same output for a certain task, whlist tolerating a small amount of rounding errors. Typically, a software writer can keep many versions of a function as a documentation of each optimization / algorithm rewrite that takes place. How does one make these versions available for others to study their optimization techniques?

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  • Tree position terminology/naming

    - by wst
    This is a naming things question. I am processing trees (XML documents), and there are often special rules applied to nodes based on structure. It's been very difficult coming up with concise naming conventions for some cases, namely for nodes in the first position among their siblings, along with some recursive relationship: Given an arbitrary node, I want to describe its first child, and then that node's first child, and so on recursively. Given another arbitrary node, I want to describe its parent if the parent is first among its siblings, and that parent's parent if it's first, and so on recursively. Is there existing terminology to describe these tree positions? How would you name a variable or function that captures one of these cases so that it's intuitive to an unfamiliar developer trying to understand an algorithm?

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  • About floating point precision and why do we still use it

    - by system_is_b0rken
    Floating point has always been troublesome for precision on large worlds. This article explains behind-the-scenes and offers the obvious alternative - fixed point numbers. Some facts are really impressive, like: "Well 64 bits of precision gets you to the furthest distance of Pluto from the Sun (7.4 billion km) with sub-micrometer precision. " Well sub-micrometer precision is more than any fps needs (for positions and even velocities), and it would enable you to build really big worlds. My question is, why do we still use floating point if fixed point has such advantages? Most rendering APIs and physics libraries use floating point (and suffer it's disadvantages, so developers need to get around them). Are they so much slower? Additionally, how do you think scalable planetary engines like outerra or infinity handle the large scale? Do they use fixed point for positions or do they have some space dividing algorithm?

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  • What web oriented language would work best with binary data?

    - by Qqwy
    I want to create a service where people can upload files. However, since file storage costs money, I want to compress the files so they take less space. I would want to write my own compression algorithm, however, PHP doesn't have good ways to handle binary data (which is needed for many compression algorithms). So I wondered, what would be a better language to create such a website in? I have knowledge of PHP (and Javascript, HTML and CSS) but no experience with other things like Ruby, Perl, Python, and other web development languages.

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  • k-d tree implementation [closed]

    - by user466441
    when i run my code and debugged,i got this error - this 0x00093584 {_Myproxy=0x00000000 _Mynextiter=0x00000000 } std::_Iterator_base12 * const - _Myproxy 0x00000000 {_Mycont=??? _Myfirstiter=??? } std::_Container_proxy * _Mycont CXX0017: Error: symbol "" not found _Myfirstiter CXX0030: Error: expression cannot be evaluated + _Mynextiter 0x00000000 {_Myproxy=??? _Mynextiter=??? } std::_Iterator_base12 * but i dont know what does it means,code is this #include<iostream> #include<vector> #include<algorithm> using namespace std; struct point { float x,y; }; vector<point>pointleft(4); vector<point>pointright(4); //we are going to implement two comparison function for x and y coordinates,we need it in calculation of median (we should sort vector //by x or y according to depth informaton,is depth even or odd. bool sortby_X(point &a,point &b) { return a.x<b.x; } bool sortby_Y(point &a,point &b) { return a.y<b.y; } //so i am going to implement to median finding algorithm,one for finding median by x and another find median by y point medianx(vector<point>points) { point temp; sort(points.begin(),points.end(),sortby_X); temp=points[(points.size()/2)]; return temp; } point mediany(vector<point>points) { point temp; sort(points.begin(),points.end(),sortby_Y); temp=points[(points.size()/2)]; return temp; } //now construct basic tree structure struct Tree { float x,y; Tree(point a) { x=a.x; y=a.y; } Tree *left; Tree *right; }; Tree * build_kd( Tree *root,vector<point>points,int depth) { point temp; if(points.size()==1)// that point is as a leaf { if(root==NULL) root=new Tree(points[0]); return root; } if(depth%2==0) { temp=medianx(points); root=new Tree(temp); for(int i=0;i<points.size();i++) { if (points[i].x<temp.x) pointleft[i]=points[i]; else pointright[i]=points[i]; } } else { temp=mediany(points); root=new Tree(temp); for(int i=0;i<points.size();i++) { if(points[i].y<temp.y) pointleft[i]=points[i]; else pointright[i]=points[i]; } } return build_kd(root->left,pointleft,depth+1); return build_kd(root->right,pointright,depth+1); } void print(Tree *root) { while(root!=NULL) { cout<<root->x<<" " <<root->y; print(root->left); print(root->right); } } int main() { int depth=0; Tree *root=NULL; vector<point>points(4); float x,y; int n=4; for(int i=0;i<n;i++) { cin>>x>>y; points[i].x=x; points[i].y=y; } root=build_kd(root,points,depth); print(root); return 0; } i am trying ti implement in c++ this pseudo code tuple function build_kd_tree(int depth, set points): if points contains only one point: return that point as a leaf. if depth is even: Calculate the median x-value. Create a set of points (pointsLeft) that have x-values less than the median. Create a set of points (pointsRight) that have x-values greater than or equal to the median. else: Calculate the median y-value. Create a set of points (pointsLeft) that have y-values less than the median. Create a set of points (pointsRight) that have y-values greater than or equal to the median. treeLeft = build_kd_tree(depth + 1, pointsLeft) treeRight = build_kd_tree(depth + 1, pointsRight) return(median, treeLeft, treeRight) please help me what this error means?

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  • How to implement the setup rules like Clash of Clan?

    - by user25959
    Now I'm already implement the setup build rules which the building could move by unit grid width and height. But the validation detection is poor efficiency. The algorithm cost me 10~12(ms) in average when I move the building. Here is my approach to that: 1.Basic Grid, it is a two dimensional array. Grid[row][column], so that I can save info for each grid. Like whether is it in occupied or excluded. 2.Exclude Space, this is a space which limit same building numbers in space.

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  • Flowchart for solving programming problems

    - by nurne
    I noticed that every developer implements a somewhat different flowchart for solving programming problems. By flowchart I mean a defined system of techniques that the developer goes through in a certain sequence, trying to solve the problem at hand. Some examples for techniques: Google "how to..." or "... tutorial". Search the java/msdn/apple/etc API doc for the specific class or method. Search in stack overflow the exact problem with some tags like [iphone]/[java] etc. Take a nap and let the subconscious work. Debug. Draw the algorithm or system. Google the logged error message. Ask a colleague or manager. Ask a new question in stack overflow. From your experience, what is the best flowchart for solving a programming problem?

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  • The how of a collision engine

    - by JXPheonix
    This is a very, very broad question - what is the general algorithm of how a collision engine works? No code in specific, but rather, just a general idea of how a collision engine does what it does, constantly refreshing the points of an object and comparing it to other objects? (see, I have the general gist of it here.) A collision engine is basically an engine used in games (generally) so that your player (call him Bob), whenever bob moves into a wall, Bob stops, Bob does not walk through the wall. They also generally handle the gravity in a game and environmental things like that.

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  • How can I generate signed distance fields in real time, fast?

    - by heishe
    In a previous question, it was suggested that signed distance fields can be precomputed, loaded at runtime and then used from there. For reasons I will explain at the end of this question (for people interested), I need to create the distance fields in real time. There are some papers out there for different methods which are supposed to be viable in real-time environments, such as methods for Chamfer distance transforms and Voronoi diagram-approximation based transforms (as suggested in this presentation by the Pixeljunk Shooter dev guy), but I (and thus can be assumed a lot of other people) have a very hard time actually putting them to use, since they're usually long, largely bloated with math and not very algorithmic in their explanation. What algorithm would you suggest for creating the distance fields in real-time (favourably on the GPU) especially considering the resulting quality of the distance fields? Since I'm looking for an actual explanation/tutorial as opposed to a link to just another paper or slide, this question will receive a bounty once it's eligible for one :-). Here's why I need to do it in real time:

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  • Inexpensive generation of hierarchical unique IDs

    - by romaninsh
    My application is building a hierarchical structure like this: root = { 'id': 'root', 'children': [ { 'name': 'root_foo', 'children': [] }, { 'id': 'root_foo2', 'children': [ { 'id': 'root_foo2_bar', 'children': [] } ] } ] } in other words, it's a tree of nodes, where each node might have child elements and unique identifier I call "id". When a new child is added, I need to generate a unique identifier for it, however I have two problems: identifiers are getting too long adding many children takes slower, as I need to find first available id My requirement is: naming of a child X must be determined only from the state in their ancestors When I re-generate tree with same contents, the IDs must be same or in other words, when we have nodes A and B, creating child in A, must not affect the name given to children of B. I know that one way to optimize would be to introduce counter in each node and append it to the names which will solve my performance issue, but will not address the issue with the "long identifiers". Could you suggest me the algorithm for quickly coming up with new IDs?

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  • Implementing ASP.NET 4.0 Page.MetaDescription Property

    Before ASP.NET 4.0, you had to manually code your meta description tags. The meta description tag, though no longer used by major search engines in their ranking algorithm, is still an important factor for increasing website traffic. Bear in mind that searchers coming from search engines (such as Google) will only click on the results provided if the meta description is relevant to the query. If you want to increase your organic traffic (traffic coming from search engines) then one thing that you can easily improve are the meta descriptions. In ASP.NET 4.0, this can be easily implemented using...

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  • Interview question ranking FizzBuzz (1), implementing malloc (10)

    - by blrs
    I'd like to have your opinion on the difficulty of the following interview question: Find the subarray with maximum sum in an array of integers in O(n) time. This trivial sounding problem was made famous by Jon Bentley in his Programming Pearls where he uses it to demonstrate algorithm design techniques. On a scale of 1-10, 1 being the FizzBuzz (or HoppityHop) test and 10 being implement the C stdlib function malloc(), how would you rank the above problem? I think the people who can best answer this question are those who have read Programming Pearls and have tried to solve this problem on their own. To motivate those who haven't, 'Programming Pearls' gets featured many times in the 'Top 10 programming books' list.

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  • How to understand Linux kernel source code for a beginner?

    - by user16867
    I am a student interested in working on Memory Management, particularly the page replacement component of the linux kernel. What are the different guides that can help me to begin understanding the kernel source? I have tried to read the book Understanding the Linux Virutal Memory Manager by Mel Gorman and Understanding the Linux Kernel by Cesati and Bovet, but they do not explain the flow of control through the code. They only end up explaining various data structures used and the work various functions perform. This makes the code more confusing. My project deals with tweaking the page replacement algorithm in a mainstream kernel and analyse its performance for a set of workloads. Is there a flavor of the linux kernel that would be easier to understand(if not the linux-2.6.xx kernel)?

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  • What is the logic behind this C Program?

    - by iamanimesh19
    Here is a small piece of program (14 lines of program) which counts the number of bits set in a number. Input-Output -- 0--0(0000000), 5--2(0000101), 7--3(0000111) int CountBits (unsigned int x) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF } ; int i ; int shift ; /* Number of positions to shift to right*/ for (i =0, shift =1; i < 5; i ++, shift *= 2) x = (x & mask[i ])+ ( ( x >> shift) & mask[i]); return x; } Can someone explain the algorithm used here/why this works?

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  • How can I fix latency problems for car game?

    - by Freddy
    Basically I'm trying to make a online car racing game for IOS using Game Center real time multiplayer. I have setup a timer that sends data every 0.02 seconds to the other player with the current position and current angle. However sometimes, it will take LONGER then these 0.02 seconds for the package to be sent and then received. In this case i have implemented a method that "calculate" what the next position should be if no position is received based on the last position and angle. However, when the data then receives for let say 0.04 seconds after, it will change back to the last position, which will result in the car "jumping" back and lag. And If i just keep ignoring the data it will never take any input from the other user. Is their any way to prevent this? I suppose this needs to be fixed with some client-sided algorithm.

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  • Algorithms for positioning rectangles evenly spaced with unknown connecting lines

    - by MacGyver
    I'm new to game development, but I'm trying to figure out a good algorithm for positioning rectangles (of any width and height) in a given surface area, and connecting them with any variation of lines. Two rectangles will never have more than one line connecting them. Where would I begin working on a problem like this? This is only a 2 dimensional surface. I read about graph theory, and it seems like this is a close representation of that. The rectangles would be considered a node, and the lines connecting them would be considered an edge in graph theory.

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  • Twitter Customer Sentiment Analysis

    - by Liam McLennan
    The breakable toy that I am currently working on is a twitter customer sentiment analyser. It scrapes twitter for tweets relating to a particular organisation, applies a machine learning algorithm to determine if the content of tweet is positive or negative, and generates reports of the sentiment data over time, correlated to dates, events and news feeds. I’m having lots of fun building this, but I would also like to learn if there is a market for quantified sentiment data. So that I can start to show people what I have in mind I have created a mockup of the simplest and most important report. It shows customer sentiment over time, with important events highlighted. As the user moves their mouse to the right (forward in time) the source data area scrolls up to display the tweets from that time. The tweets are colour coded based on sentiment rating. After I started working on this project I discovered that a team of students have already built something similar. It is a lot of fun to enter your employers name and see what it says.

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  • Developing an AI opponent for Monopoly

    - by Bernhard Zürn
    i want to develop an AI opponent for the Board Game Monopoly. I want to implement the whole Game with Prolog (XPCE). The probability for a field on the Board being hit, can be computed with Markov Chains. I already know some "best practices" like "after 50% of the playing time it does not make sense to buy out of jail because in jail you get renting fees for your fields but you don't have to pay for other fields as long as you stay in prison". The interesting question always is: buy a streetfield ? buy houses / hotels ? how much ? so i think i would have to compute some kind of future liquidity .. does anyone know how to pack that into an algorithm or how to translate it to prolog ?

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  • Map, Set use cases in a general web app

    - by user2541902
    I am currently working on my own Java web app (to be shown in interview to get a Java job). So I've not worked on Java in professional environment, so no guidance. I have database, entity classes, JPA relationships. Use cases are like, user has albums, album has pics, user has locations, location has co-ordinates etc. I used List (ArrayList) everywhere. I can do anything with List and DB, get some entry, find etc. For example, I will keep the list of users in List, then use queries to get some entry (why would I keep them in Map with id/email as key?). I know very well the working and features, implementing classes of Map, Set. I can use them for solving some algorithm, processing some data etc. In interviews, I get asked have you worked with these, where have you used them etc. So, Please tell me cases where they should be used (DB or any popular real use case).

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  • How to tile multiple procedurally generated textures?

    - by Burhuc
    I'm trying to develop a procedural tile generator for a game, mostly for the ground tiles, instead of using "hand-drawn" tiles. To achieve this I'm using Perlin noise and a sine wave with multiple parameters, which already gives me pretty nice results. I don't want to generate 1 tile and repeat that one forever for one ground type, but I want to avoid recurrences, so I'm generating n different tiles. The problem I'm having now is that I want to tile the generated textures (smooth transitions). At the moment I have this: 4 256x256 textures. I thought a simple method would be to just add the positions of the different tiles to the noise generation algorithm, so that, when creating the 4 256x256 textures, it would behave like it would create a 512x512 texture, but that somehow didn't work as intented. So how can I tile those textures?

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