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• Vector deltas and moving in unknown areas

  - by dekz

  Hi All, I was in need of a little math help that I can't seem to find the answer to, any links to documentation would be greatly appreciated. Heres my situation, I have no idea where I am in this maze, but I need to move around and find my way back to the start. I was thinking of implementing a waypoint list of places i've been offset from my start at 0,0. This is a 2D cartesian plane. I've been given 2 properties, my translation speed from 0-1 and my rotation speed from -1 to 1. -1 is very left and +1 is very right. These are speed and not angles so thats where my problem lies. If I'm given 0 as a translation speed and 0.2 I will continually turn to my right at a slow speed. How do I figure out the offsets given these 2 variables? I can store it every time I take a 'step'. I just need to figure out the offsets in x and y terms given the translations and rotation speeds. And the rotation to get to those points. Any help is appreciated.

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• How to Check Authenticity of an AJAX Request

  - by Alex Reisner

  I am designing a web site in which users solve puzzles as quickly as they can. JavaScript is used to time each puzzle, and the number of milliseconds is sent to the server via AJAX when the puzzle is completed. How can I ensure that the time received by the server was not forged by the user? I don't think a session-based authenticity token (the kind used for forms in Rails) is sufficient because I need to authenticate the source of a value, not just the legitimacy of the request. Is there a way to cryptographically sign the request? I can't think of anything that couldn't be duplicated by a hacker. Is any JavaScript, by its exposed, client-side nature, subject to tampering? Am I going to have to use something that gets compiled, like Flash? (Yikes.) Or is there some way to hide a secret key? Or something else I haven't thought of? Update: To clarify, I don't want to penalize people with slow network connections (and network speed should be considered inconsistent), so the timing needs to be 100% client-side (the timer starts only when we know the user can see the puzzle). Also, there is money involved so no amount of "trusting the user" is acceptable.

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• R optimization: How can I avoid a for loop in this situation?

  - by chrisamiller

  I'm trying to do a simple genomic track intersection in R, and running into major performance problems, probably related to my use of for loops. In this situation, I have pre-defined windows at intervals of 100bp and I'm trying to calculate how much of each window is covered by the annotations in mylist. Graphically, it looks something like this: 0 100 200 300 400 500 600 windows: |-----|-----|-----|-----|-----|-----| mylist: |-| |-----------| So I wrote some code to do just that, but it's fairly slow and has become a bottleneck in my code: ##window for each 100-bp segment windows <- numeric(6) ##second track mylist = vector("list") mylist[[1]] = c(1,20) mylist[[2]] = c(120,320) ##do the intersection for(i in 1:length(mylist)){ st <- floor(mylist[[i]][1]/100)+1 sp <- floor(mylist[[i]][2]/100)+1 for(j in st:sp){ b <- max((j-1)*100, mylist[[i]][1]) e <- min(j*100, mylist[[i]][2]) windows[j] <- windows[j] + e - b + 1 } } print(windows) [1] 20 81 101 21 0 0 Naturally, this is being used on data sets that are much larger than the example I provide here. Through some profiling, I can see that the bottleneck is in the for loops, but my clumsy attempt to vectorize it using *apply functions resulted in code that runs an order of magnitude more slowly. I suppose I could write something in C, but I'd like to avoid that if possible. Can anyone suggest another approach that will speed this calculation up?

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• Overlapping audio in IE when I show/hide videos

  - by user1062448

  I have a thumbnail list with links to individual videos. Everything works fine in all browsers but IE. In IE, if I start a video and (without slicking pause or stop) click on the thumbnail for the next video, the audio continues playing. In other words, the audio for both videos plays at once. Any suggestions? HTML: <ul class="videoButtons"> <li><a class="vidButton" href="javascript:void(0)" id="1" ><img src="images/videoPics/vid1Thumb.jpg" /><br />video title</a></li> <li><a class="vidButton" href="javascript:void(0)" id="2" ><img src="images/videoPics/vid2Thumb.jpg" /><br />video title</a></li> <li><a class="vidButton" href="javascript:void(0)" id="3" ><img src="images/videoPics/vid3Thumb.jpg" /><br />video title</a></li> </ul> <div class="box" id="video1"> <!--flv embedded object - FLVPlayer--> </div> <div class="box" id="video2"> <!--flv embedded object - FLVPlayer1--> </div> <div class="box" id="video3"> <!--flv embedded object - FLVPlayer2--> </div> Show/Hide code: $(".vidButton").click(function() { var buttonID = $(this).attr('id'); // get ID of the button clicked var video = $('#'+'video'+buttonID); // add ID number to video $('.box').hide(); // hide all other divs video.fadeTo("slow", 1); // show video }); }); // video objects swfobject.registerObject("FLVPlayer"); swfobject.registerObject("FLVPlayer1"); swfobject.registerObject("FLVPlayer2");

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• Effective simulation of compound poisson process in Matlab

  - by Henrik

  I need to simulate a huge bunch of compound poisson processes in Matlab on a very fine grid so I am looking to do it most effectively. I need to do a lot of simulations on the same random numbers but with parameters changing so it is practical to draw the uniforms and normals beforehand even though it means i have to draw a lot more than i will probably need and won't matter much because it will only need to be done once compared to in the order 500*n repl times the actual compound process generation. My method is the following: Let T be for how long i need to simulate and N the grid points, then my grid is: t=linspace(1,T,N); Let nrepl be the number of processes i need then I simulate P=poissrnd(lambda,nrepl,1); % Number of jumps for each replication U=(T-1)*rand(10000,nrepl)+1; % Set of uniforms on (1,T) for jump times N=randn(10000,nrepl); % Set of normals for jump size Then for replication j: Poiss=P(j); % Jumps for replication Uni=U(1:Poiss,j);% Jump times Norm=mu+sigma*N(1:Poiss,j);% Jump sizes Then this I guess is where I need your advice, I use this one-liner but it seems very slow: CPP_norm=sum(bsxfun(@times,bsxfun(@gt,t,Uni),Norm),1); In the inner for each jump it creates a series of same length as t with 0 until jump and then 1 after, multiplying this will create a grid with zeroes until jump has arrived and then the jump size and finally adding all these will produce the entire jump process on the grid. How can this be done more effectively? Thank you very much.

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• Python : How do you find the CPU consumption for a piece of code?

  - by Yugal Jindle

  Background: I have a django application, it works and responds pretty well on low load, but on high load like 100 users/sec, it consumes 100% CPU and then due to lack of CPU slows down. Problem : Profiling the application gives me time taken by functions. This time increases on high load. Time consumed may be due to complex calculation or for waiting for CPU. so, how to find the CPU cycles consumed by a piece of code ? Since, reducing the CPU consumption will increase the response time. I might have written extremely efficient code and need to add more CPU power OR I might have some stupid code taking the CPU and causing the slow down ? Any help is appreciated ! Update: I am using Jmeter to profile my webapp, it gives me a throughput of 2 requests/sec. [ 100 users] I get a average time of 36 seconds on 100 request vs 1.25 sec time on 1 request. More Info Configuration Nginx + Uwsgi with 4 workers No database used, using a responses from a REST API On 1st hit the response of REST API gets cached, therefore doesn't makes a difference. Using ujson for json parsing. Curious to Know: Python-Django is used by so many orgs for so many big sites, then there must be some high end Debug / Memory-CPU analysis tools. All those I found were casual snippets of code that perform profiling.

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• Implimenting Zend MVC for my existing site-first step?

  - by Joel

  Hi guys, OK-newbie question here. I'll try not to bombard SO with lots of questions-and hopefully this first one will show me the method I'll need to follow for subsequent conversions. I have a web-based calendar system that I developed, but it was coded for me procedurally (using PHP). I'm now working on learning OO and wanting to integrate this site into my localhost Zend Framework and slowly start converting parts to OO and the Zend Framework MVC process in particular. As I've said before, I understand that this will be a slow process, and when I'm done, I still probably won't have anything as OO friendly as if I had rewritten it from scratch, but I'd like to use this as a learning experience. So, I have dropped the whole site into my localhose/zend/Public folder, and everything is showing up great and linking to the database, etc. My question is-what would be the easiest first component to switch over to the MVC model? This site has a bit of everything-forms, login, authentication, some jQuery, etc. Can anyone point to a tutorial that would address what I'm trying to do? If indeed, a form would be one of the simpler things to switch, can someone walk me through those changes? Another idea is changing over all the header info, etc? Thanks for any pointers on where to start! EDIT: Also, I understand that SO is mainly for specific coding questions-I'm happy to share specific code, once I have an idea about which section to tackle first...

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• PHP and storing stats

  - by John

  Using PHP5 and the latest version of MySQL I want to be able to track impressions and clicks for business listings. My question is if I did this myself what would be the best method in storing it so I can run reports? Before I just had a table that had the listing id, user ip address and if it was a click or impression as well as the date it was tracked. However the database itself is approaching 2GB of data and its very slow, part of the problem is its a pretty simple script that includes impressions and clicks from anyone including search engines and basically anyone or anything that accesses the listing page. Is there an api or file out there that has an update to date list that can detect if the person viewing is a actually person and not a spider so I dont fill up the database with unneeded stats? Just looking for suggestions, do I just have a raw database that gets just the hits then a cron job at night tally up for the day for each listing for each ip and store the cumulative stats in a different table? Also what type of database should it be? Innodb? MyISAM?

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• If Statements Skipping or Evaluating Strangely, JavaScript and jquery

  - by tlm2021

  So in jQuery, I have a global variable "currentSubNav" that stores a current visible element. The following code executes on "mouseenter". I need it to get store element's ID, check to see if there was one. If there wasn't, set the new visible element to the default. $('#mainMenu a').mouseenter(function() { var newName = $(this).attr("id"); if(newName == ''){ var newName = "default"; } Then it checks to see if the new element matches the current one. If so, it returns. If not, it performs the animations to bring in the new one. if(newName == currentSubNav){ return; }else{ $("div[name=" + currentSubNav + "]").animate({"left": "+=600px", "opacity": "toggle"}, "slow"); $("div[name=" + newName + "]").css({"margin-top": "0"}); $("div[name=" + newName + "]").fadeIn(2000); $("div[name=" + currentSubNav + "]").animate({"left": "-=600px"}, 0); currentSubNav = newName; return; } }); I'm using Chrome at the moment, and according to the dev tools that isn't what happens. Problem #1 "$(this).attr("id");" isn't returning undefined as the documentation claims. It seems to be returning "". BUT, when I have the if statement as I do above, it skips over the statement entirely. I set a breakpoint, but it never pauses execuation, so the statement is never evaluated. Problem #2 After the animations occur, instead of using the return at the end of the statements it goes back and uses the return for the "newName == currentSubNav" if statement. I guess that not a big deal, but it's not the intended behavior. I'm fairly new to JavaScript, and it appears I'm missing something about how JavaScript works. But I can't find what anywhere. Any help? Blockquote

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• Running a process at the Windows 7 Welcome Screen

  - by peelman

  So here's the scoop: I wrote a tiny C# app a while back that displays the hostname, ip address, imaged date, thaw status (we use DeepFreeze), current domain, and the current date/time, to display on the welcome screen of our Windows 7 lab machines. This was to replace our previous information block, which was set statically at startup and actually embedded text into the background, with something a little more dynamic and functional. The app uses a Timer to update the ip address, deepfreeze status, and clock every second, and it checks to see if a user has logged in and kills itself when it detects such a condition. If we just run it, via our startup script (set via group policy), it holds the script open and the machine never makes it to the login prompt. If we use something like the start or cmd commands to start it off under a separate shell/process, it runs until the startup script finishes, at which point Windows seems to clean up any and all child processes of the script. We're currently able to bypass that using psexec -s -d -i -x to fire it off, which lets it persist after the startup script is completed, but can be incredibly slow, adding anywhere between 5 seconds and over a minute to our startup time. We have experimented with using another C# app to start the process, via the Process class, using WMI Calls (Win32_Process and Win32_ProcessStartup) with various startup flags, etc, but all end with the same result of the script finishing and the info block process getting killed. I tinkered with rewriting the app as a service, but services were never designed to interact with the desktop, let alone the login window, and getting things operating in the right context never really seemed to work out. So for the question: Does anybody have a good way to accomplish this? Launch a task so that it would be independent of the startup script and run on top of the welcome screen?

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• sending large data .getJSON or proxy ?

  - by numerical25

  Hey guys. I was told that the only trick to sending data to a external server (i.e x-domain) is to use getJSON. Well my problem is that the data I am sending exceeds the getJSON data limit. I am tracking mouse movements on a screen for analytics. Another option is I could also send a little data at a time. probably every time the mouse moves. but that seems as if it would slow things down. I could setup a proxy server. My question is which would be better? Setting up a proxy server ? or Just sending bits of information via javascript or JQUERY. What do the professionals use (Google and other company's that build mash-ups that send a lot of data to x-domain sites.) I need to know the best practices. Thanx!! Also the data is put into JSON.

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• Too many columns to index - use mySQL Partitions?

  - by Christopher Padfield

  We have an application with a table with 20+ columns that are all searchable. Building indexes for all these columns would make write queries very slow; and any really useful index would often have to be across multiple columns increasing the number of indexes needed. However, for 95% of these searches, only a small subset of those rows need to be searched upon, and quite a small number - say 50,000 rows. So, we have considered using mySQL Partition tables - having a column that is basically isActive which is what we divide the two partitions by. Most search queries would be run with isActive=1. Most queries would then be run against the small 50,000 row partition and be quick without other indexes. Only issue is the rows where isActive=1 is not fixed; i.e. it's not based on the date of the row or anything fixed like that; we will need to update isActive based on use of the data in that row. As I understand it that is no problem though; the data would just be moved from one partition to another during the UPDATE query. We do have a PK on id for the row though; and I am not sure if this is a problem; the manual seemed to suggest the partition had to be based on any primary keys. This would be a huge problem for us because the primary key ID has no basis on whether the row isActive.

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• printing out dictionnaires

  - by kyril

  I have a rather specific question: I want to print out characters at a specific place using the \033[ syntax. This is what the code below should do: (the dict cells has the same keys as coords but with either '*' or '-' as value.) coords = {'x'+str(x)+'y'+str(y) : (x,y) for x,y, in itertools.product(range(60), range(20))} for key, value in coords.items(): char = cells[key] x,y = value HORIZ=str(x) VERT=str(y) char = str(char) print('\033['+VERT+';'+HORIZ+'f'+char) However, I noticed that if I put this into a infinite while loop, it does not always prints the same characters at the same position. There are only slight changes, but it deletes some and puts them back in after some loops. I already tried it with lists, and there it seems to behave just fine, so I tend to think it has something todo with the dict, but I can not figure out what it could be. You can see the Problem in a console here: SharedConsole.I am happy for every tip on this matter. On a related topic: After the printing, some changes should be made at the values of the cells dict, but for reason unknown to me, the only the first two rules are executed and the rest is ignored. The rules should test how many neighbours (which is in population) are around the cell and apply the according rule. In my implemention of this I have some kind of weird tumor growth (which should not happen, as if there more than three around they should the cell should die) (see FreakingTumor): if cells_copy [coord] == '-': if population == 3: cells [coord] = '*' if cells_copy [coord] == '*': if population > 3: cells [coord] = '-' elif population <= 1: cells [coord] = '-' elif population == 2 or 3: cells [coord] = '*' I checked the population variable several times, so I am quite sure that is not the matter. I am sorry for the slow consoles. Thanks in advance! Kyril

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• R Random Data Sets within loops

  - by jugossery

  Here is what I want to do: I have a time series data frame with let us say 100 time-series of length 600 - each in one column of the data frame. I want to pick up 4 of the time-series randomly and then assign them random weights that sum up to one (ie 0.1, 0.5, 0.3, 0.1). Using those I want to compute the mean of the sum of the 4 weighted time series variables (e.g. convex combination). I want to do this let us say 100k times and store each result in the form ts1.name, ts2.name, ts3.name, ts4.name, weight1, weight2, weight3, weight4, mean so that I get a 9*100k df. I tried some things already but R is very bad with loops and I know vector oriented solutions are better because of R design. Thanks Here is what I did and I know it is horrible The df is in the form v1,v2,v2.....v100 1,5,6,.......9 2,4,6,.......10 3,5,8,.......6 2,2,8,.......2 etc e=NULL for (x in 1:100000) { s=sample(1:100,4)#pick 4 variables randomly a=sample(seq(0,1,0.01),1) b=sample(seq(0,1-a,0.01),1) c=sample(seq(0,(1-a-b),0.01),1) d=1-a-b-c e=c(a,b,c,d)#4 random weights average=mean(timeseries.df[,s]%*%t(e)) e=rbind(e,s,average)#in the end i get the 9*100k df } The procedure runs way to slow. EDIT: Thanks for the help i had,i am not used to think R and i am not very used to translate every problem into a matrix algebra equation which is what you need in R. Then the problem becomes a little bit complex if i want to calculate the standard deviation. i need the covariance matrix and i am not sure i can if/how i can pick random elements for each sample from the original timeseries.df covariance matrix then compute the sample variance (t(sampleweights)%*%sample_cov.mat%*%sampleweights) to get in the end the ts.weighted_standard_dev matrix Last question what is the best way to proceed if i want to bootstrap the original df x times and then apply the same computations to test the robustness of my datas thanks

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• Doing some downloading without blocking you app

  - by Code

  Hi guys, I'm working on my first app that's doing a few different web connections at once. My first screen is my Menu. And at the bottom of viewDidLoad of MenuViewController i call a method that gets and parses a .xml file that is located on my webserver. Also at the bottom of viewDidLoad i do FootballScores = [[FootBallScores alloc] init]; and FootballScores makes a connection to a html page which it loads into a string and then parses out data. Now since both of these are getting called at the bottom of viewDidLoad of the class thats is responsible for the main menu(first screen in the app) it means the app is kinda slow to load. What is the right way to do the above? Should i remove the 2 pieces of code from my viewDidLoad and replace with maybe dataGetterOne = [NSTimer scheduledTimerWithTimeInterval:1.000 target:self selector:@selector(xmlParser) userInfo:nil repeats:NO]; dataGetterTwo = [NSTimer scheduledTimerWithTimeInterval:2.000 target:self selector:@selector(htmlParser) userInfo:nil repeats:NO]; This would mean that the methods get called later on and the viewDidLoad gets to finish before the i try get the data from the web servers. Making 2 connections to we bservers a second apart to quick? Can the iphone handle having 2 connections open at once? I'm really unsure of anything bad/dangerous I am doing in regards to connections. Many Thanks -Code

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• Is it possible to cache all the data in a SQL Server CE database using LinqToSql?

  - by DanM

  I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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• How do software events work internally?

  - by Duddle

  Hello! I am a student of Computer Science and have learned many of the basic concepts of what is going on "under the hood" while a computer program is running. But recently I realized that I do not understand how software events work efficiently. In hardware, this is easy: instead of the processor "busy waiting" to see if something happened, the component sends an interrupt request. But how does this work in, for example, a mouse-over event? My guess is as follows: if the mouse sends a signal ("moved"), the operating system calculates its new position p, then checks what program is being drawn on the screen, tells that program position p, then the program itself checks what object is at p, checks if any event handlers are associated with said object and finally fires them. That sounds terribly inefficient to me, since a tiny mouse movement equates to a lot of cpu context switches (which I learned are relatively expensive). And then there are dozens of background applications that may want to do stuff of their own as well. Where is my intuition failing me? I realize that even "slow" 500MHz processors do 500 million operations per second, but still it seems too much work for such a simple event. Thanks in advance!

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• Concept: Information Into Memory Location.

  - by Richeve S. Bebedor

  I am having troubles conceptualizing an algorithm to be used to transform any information or data into a specific appropriate and reasonable memory location in any data structure that I will be devising. To give you an idea, I have a JPanel object instance and I created another Container type object instance of any subtype (note this is in Java because I love this language), then I collected those instances into a data structure not specifically just for those instances but also applicable to any type of object. Now my procedure for fetching those data again is to extract the object specific features similar in category to all object in that data structure and transform it into a integer data memory location (specifically as much as possible) or any type of data that will pertain to this transformation. And I can already access that memory location without further sorting or applications of O(n) time complex algorithms (which I think preferable but I wanted to do my own way XD). The data structure is of any type either binary tree, linked list, arrays or sets (and the like XD). What is important is I don't need to have successive comparing and analysis of data just to locate information in big structures. To give you a technical idea, I have to an array DS that contains JLabel object instance with a specific name "HelloWorld". But array DS contains other types of object (in multitude). Now this JLabel object has a location in the array at index [124324] (which is if you do any type of searching algorithm just to arrive at that location is conceivably slow because added to it the data structure used was an array *note please disregard the efficiency of the data structure to be used I just want to explain to you my concept XD). Now I want to equate "HelloWorld" to 124324 by using a conceptually made function applicable to all data types. So that I can do a direct search by doing this DS[extractLocation("HelloWorld")] just to get that JLabel instance. I know this may sound crazy but I want to test my concept of non-sorting feature extracting search algorithm for any data structure wherein my main problem is how to transform information to be stored into memory location of where it was stored.

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• How to make this JavaScript much faster?

  - by Ralph

  Still trying to answer this question, and I think I finally found a solution, but it runs too slow. var $div = $('<div>') .css({ 'border': '1px solid red', 'position': 'absolute', 'z-index': '65535' }) .appendTo('body'); $('body *').live('mousemove', function(e) { var topElement = null; $('body *').each(function() { if(this == $div[0]) return true; var $elem = $(this); var pos = $elem.offset(); var width = $elem.width(); var height = $elem.height(); if(e.pageX > pos.left && e.pageY > pos.top && e.pageX < (pos.left + width) && e.pageY < (pos.top + height)) { var zIndex = document.defaultView.getComputedStyle(this, null).getPropertyValue('z-index'); if(zIndex == 'auto') zIndex = $elem.parents().length; if(topElement == null || zIndex > topElement.zIndex) { topElement = { 'node': $elem, 'zIndex': zIndex }; } } }); if(topElement != null ) { var $elem = topElement.node; $div.offset($elem.offset()).width($elem.width()).height($elem.height()); } }); It basically loops through all the elements on the page and finds the top-most element beneath the cursor. Is there maybe some way I could use a quad-tree or something and segment the page so the loop runs faster?

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• C#: Any faster way of copying arrays?

  - by Yang

  I have three arrays that need to be combined in one three-dimension array. The following code shows slow performance in Performance Explorer. Is there a faster solution? for (int i = 0; i < sortedIndex.Length; i++) { if (i < num_in_left) { // add instance to the left child leftnode[i, 0] = sortedIndex[i]; leftnode[i, 1] = sortedInstances[i]; leftnode[i, 2] = sortedLabels[i]; } else { // add instance to the right child rightnode[i-num_in_left, 0] = sortedIndex[i]; rightnode[i-num_in_left, 1] = sortedInstances[i]; rightnode[i-num_in_left, 2] = sortedLabels[i]; } } Update: I'm actually trying to do the following: //given three 1d arrays double[] sortedIndex, sortedInstances, sortedLabels; // copy them over to a 3d array (forget about the rightnode for now) double[] leftnode = new double[sortedIndex.Length, 3]; // some magic happens here so that leftnode = {sortedIndex, sortedInstances, sortedLabels};

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• Find all A^x in a given range

  - by Austin Henley

  I need to find all monomials in the form AX that when evaluated falls within a range from m to n. It is safe to say that the base A is greater than 1, the power X is greater than 2, and only integers need to be used. For example, in the range 50 to 100, the solutions would be: 2^6 3^4 4^3 My first attempt to solve this was to brute force all combinations of A and X that make "sense." However this becomes too slow when used for very large numbers in a big range since these solutions are used in part of much more intensive processing. Here is the code: def monoSearch(min, max): base = 2 power = 3 while 1: while base**power < max: if base**power > min: print "Found " + repr(base) + "^" + repr(power) + " = " + repr(base**power) power = power + 1 base = base + 1 power = 3 if base**power > max: break I could remove one base**power by saving the value in a temporary variable but I don't think that would make a drastic effect. I also wondered if using logarithms would be better or if there was a closed form expression for this. I am open to any optimizations or alternatives to finding the solutions.

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• Optimized 2D Tile Scrolling in OpenGL

  - by silicus

  Hello, I'm developing a 2D sidescrolling game and I need to optimize my tiling code to get a better frame rate. As of right now I'm using a texture atlas and 16x16 tiles for 480x320 screen resolution. The level scrolls in both directions, and is significantly larger than 1 screen (thousands of pixels). I use glTranslate for the actual scrolling. So far I've tried: Drawing only the on-screen tiles using glTriangles, 2 per square tile (too much overhead) Drawing the entire map as a Display List (great on a small level, way to slow on a large one) Partitioning the map into Display Lists half the size of the screen, then culling display lists (still slows down for 2-directional scrolling, overdraw is not efficient) Any advice is appreciated, but in particular I'm wondering: I've seen Vertex Arrays/VBOs suggested for this because they're dynamic. What's the best way to take advantage of this? If I simply keep 1 screen of vertices plus a bit of overdraw, I'd have to recopy the array every few frames to account for the change in relative coordinates (shift everything over and add the new rows/columns). If I use more overdraw this doesn't seem like a big win; it's like the half-screen display list idea. Does glScissor give any gain if used on a bunch of small tiles like this, be it a display list or a vertex array/VBO Would it be better just to build the level out of large textures and then use glScissor? Would losing the memory saving of tiling be an issue for mobile development if I do this (just curious, I'm currently on a PC)? This approach was mentioned here Thanks :)

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• Many users, many cpus, no delays. Good for cloud?

  - by Eric

  I wish to set up a CPU-intensive time-important query service for users on the internet. A usage scenario is described below. Is cloud computing the right way to go for such an implementation? If so, what cloud vendor(s) cater to this type of application? I ask specifically, in terms of: 1) pricing 2) latency resulting from: - slow CPUs, instance creations, JIT compiles, etc.. - internal management and communication of processes inside the cloud (e.g. a queuing process and a calculation process) - communication between cloud and end user 3) ease of deployment A usage scenario I am expecting is: - A typical user sends a query (XML of size around 1K) once every 30 seconds on average. - Each query requires a numerical computation of average time 0.2 sec and max time 1 sec on a 1 GHz Pentium. The computation requires no data other than the query itself and is performed by the same piece of code each time. - The delay a user experiences between sending a query and receiving a response should be on average no more than 2 seconds and in general no more than 5 seconds. - A background save to a DB of the response should occur (not time critical) - There can be up to 30000 simultaneous users - i.e., on average 1000 queries a second, each requiring an average 0.2 sec calculation, so that would necessitate around 200 CPUs. Currently I'm look at GAE Java (for quicker deployment and less IT hassle) and EC2 (Speed and price optimization) as options. Where can I learn more about the right way to set ups such a system? past threads, different blogs, books, etc.. BTW, if my terminology is wrong or confusing, please let me know. I'd greatly appreciate any help.

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• jQuery and MySQL

  - by Wayne

  I have taken a jQuery script which would remove divs on a click, but I want to implement deleting records of a MySQL database. In the delete.php: <?php $photo_id = $_POST['id']; $sql = "DELETE FROM photos WHERE id = '" . $photo_id . "'"; $result = mysql_query($sql) or die(mysql_error()); ?> The jQuery script: $(document).ready(function() { $('#load').hide(); }); $(function() { $(".delete").click(function() { $('#load').fadeIn(); var commentContainer = $(this).parent(); var id = $(this).attr("id"); var string = 'id='+ id ; $.ajax({ type: "POST", url: "delete.php", data: string, cache: false, success: function(){ commentContainer.slideUp('slow', function() {$("#photo-" + id).remove();}); $('#load').fadeOut(); } }); return false; }); }); The div goes away when I click on it, but then after I refresh the page, it appears again... How do I get it to delete it from the database? Thanks :) EDIT: Woopsie... forgot to add the db.php to it, so it works now .<

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• What is the fastest way to insert 100 000 records from one database to another?

  - by Pentium10

  I have a mobile application. My client has a large data set ~100.000 records. It's updated frequently. When we sync we need to copy from one database to another. I have attached the second database to the main, and run an insert into table select * from sync.table. This is extremely slow, it takes about 10 minutes I think. I noticed that the journal file gets increased step by step. How can I speed this up? EDITED 1 I have indexes off, and I have journal off. Using insert into table select * from sync.table it still takes 10 minutes. EDITED 2 If I run a query like select id,invitem,invid,cost from inventory where itemtype = 1 order by invitem limit 50 it takes 15-20 seconds. The table schema is: CREATE TABLE inventory ('id' INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 'serverid' INTEGER NOT NULL DEFAULT 0, 'itemtype' INTEGER NOT NULL DEFAULT 0, 'invitem' VARCHAR, 'instock' FLOAT NOT NULL DEFAULT 0, 'cost' FLOAT NOT NULL DEFAULT 0, 'invid' VARCHAR, 'categoryid' INTEGER DEFAULT 0, 'pdacategoryid' INTEGER DEFAULT 0, 'notes' VARCHAR, 'threshold' INTEGER NOT NULL DEFAULT 0, 'ordered' INTEGER NOT NULL DEFAULT 0, 'supplier' VARCHAR, 'markup' FLOAT NOT NULL DEFAULT 0, 'taxfree' INTEGER NOT NULL DEFAULT 0, 'dirty' INTEGER NOT NULL DEFAULT 1, 'username' VARCHAR, 'version' INTEGER NOT NULL DEFAULT 15 ) Indexes are created like CREATE INDEX idx_inventory_categoryid ON inventory (pdacategoryid); CREATE INDEX idx_inventory_invitem ON inventory (invitem); CREATE INDEX idx_inventory_itemtype ON inventory (itemtype); I am wondering, the insert into ... select * from isn't the fastest built-in way to do massive data copy? EDITED 3 SQLite is serverless, so please stop voting a particular answer, because that is not the answer I'm sure.

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