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• Rejigging a floating point equation ...

  - by Jamie

  I'd like to know if there is a way to improve the accuracy of calculating a slope. (This came up a few months back here). It seems by changing: float get_slope(float dXa, float dXb, float dYa, float dYb) { return (dXa - dXb)/(dYa - dYb); } to float get_slope(float dXa, float dXb, float dYa, float dYb) { return dXa/(dYa - dYb) - dXb/(dYa - dYb); } might be an improvement. Suggestions? Edit: It's precision I'm after, not efficiency.

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• Floating point precision nuances.

  - by user247077

  Hi, I found this code in NVIDIA's cuda SDK samples. void computeGold( float* reference, float* idata, const unsigned int len) { reference[0] = 0; double total_sum = 0; unsigned int i; for( i = 1; i < len; ++i) { total_sum += idata[i-1]; reference[i] = idata[i-1] + reference[i-1]; } // Here it should be okay to use != because we have integer values // in a range where float can be exactly represented if (total_sum != reference[i-1]) printf("Warning: exceeding single-precision accuracy. Scan will be inaccurate.\n"); } (C) Nvidia Corp Can somebody please tell me a case where the warning would be printed, and most importantly, why. Thank you very much.

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• Programming language for fast calculations with big integers

  - by sub

  I'm doing Project Euler problems at the moment and I can solve most of them using my own programming language which uses direct C++ integers (so they are bound to 2^32 on my machine). However, at times there are problems which require me to work with very high numbers, I can't do that with native integers. So I implemented a BigInt library in my language which unfortunately gets extremely slow at times. Is there a programming language suitable for very efficient handling of big numbers? I mean that I want to do the things I could do in other programming languages with it (variables, loops, etc.), but in a faster way. If you have got tips for workarounds of the 2^32 limit in my language/C++/other languages, please tell me too!

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• What are some useful SQL statements that should be known by all developers who may touch the Back en

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• What are some useful SQL statements / usage patterns that should be known by all developers who may

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• Managing StringBuilder Resources in C#

  - by Jim Fell

  Hello. My C# (.NET 2.0) application has a StringBuilder variable with a capacity of 2.5MB. Obviously, I do not want to copy such a large buffer to a larger buffer space every time it fills. By that point, there is so much data in the buffer anyways, removing the older data is a viable option. Can anyone see any obvious problems with how I'm doing this (i.e. am I introducing more performance problems than I'm solving), or does it look okay? tText_c = new StringBuilder(2500000, 2500000); private void AppendToText(string text) { if (tText_c.Length * 100 / tText_c.Capacity > 95) { tText_c.Remove(0, tText_c.Length / 2); } tText_c.Append(text); } Thanks.

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• a completely decoupled OO system ?

  - by shrini1000

  To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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• Efficient algorithm to distribute work?

  - by Zwei Steinen

  It's a bit complicated to explain but here we go. We have problems like this (code is pseudo-code, and is only for illustrating the problem. Sorry it's in java. If you don't understand, I'd be glad to explain.). class Problem { final Set<Integer> allSectionIds = { 1,2,4,6,7,8,10 }; final Data data = //Some data } And a subproblem is: class SubProblem { final Set<Integer> targetedSectionIds; final Data data; SubProblem(Set<Integer> targetedSectionsIds, Data data){ this.targetedSectionIds = targetedSectionIds; this.data = data; } } Work will look like this, then. class Work implements Runnable { final Set<Section> subSections; final Data data; final Result result; Work(Set<Section> subSections, Data data) { this.sections = SubSections; this.data = data; } @Override public void run(){ for(Section section : subSections){ result.addUp(compute(data, section)); } } } Now we have instances of 'Worker', that have their own state sections I have. class Worker implements ExecutorService { final Map<Integer,Section> sectionsIHave; { sectionsIHave = {1:section1, 5:section5, 8:section8 }; } final ExecutorService executor = //some executor. @Override public void execute(SubProblem problem){ Set<Section> sectionsNeeded = fetchSections(problem.targetedSectionIds); super.execute(new Work(sectionsNeeded, problem.data); } } phew. So, we have a lot of Problems and Workers are constantly asking for more SubProblems. My task is to break up Problems into SubProblem and give it to them. The difficulty is however, that I have to later collect all the results for the SubProblems and merge (reduce) them into a Result for the whole Problem. This is however, costly, so I want to give the workers "chunks" that are as big as possible (has as many targetedSections as possible). It doesn't have to be perfect (mathematically as efficient as possible or something). I mean, I guess that it is impossible to have a perfect solution, because you can't predict how long each computation will take, etc.. But is there a good heuristic solution for this? Or maybe some resources I can read up before I go into designing? Any advice is highly appreciated!

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• MySQL IDE recommendation?

  - by Maxim Veksler

  Hello, I've been wondering what you guys are using to write,debug,test your SQL queries there days? The requirements are quite simple: Auto-complete Syntax Highlighting SQL Hisotry Good UI There are some tools which are common for this task, each with his own problems. To name a few Mysql Query Browser MySQL Workbench (GA?, Beta?) Eclipse Database development perspective Oracle SQL Developer with Connector/J I won't go into why none of them is perfect, trust me they all have their problems. So, what are you guys using?

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• Real-Time Data Streaming to Multiple Clients

  - by AriX

  Hi all, I would like to write an application which will stream data at 2400 baud over the internet from a server to multiple clients. The data will be the same for each client, and it would probably be fine to send it as a UDP stream, since exact data accuracy is not a 100% necessity, as there are checksums built-in to the data format and the data will be sent repeatedly on a loop. What is the best way to do this? I would want to write the server in C, but I don't know how to best multicast this data to the different clients that would be receiving it all over the country. I'm sure this seems like a pretty draconian way to go about my project, as opposed to just using some sort of fetch command, but I'd prefer to do it this way if possible.

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• ClickOnce deployment with VS2008 - prerequisites not installing on Windows 7 (only)

  - by dataft

  I have a VS2008 clickonce application with a custom prerequiste, which I install with the bootstrapper. When deployed online, the prerequisite is downloaded and installed fine. No problems. When deployed via CD to a Windows XP machine, also fine as above. No problems. However, when deployed via CD to a Windows 7 machine: the prerequisite is downloaded - good then the user is asked for permission to the run the file - good then the installation of the prerequiste is just SKIPPED - bad and the ClickOnce application installation begins without the prerequisite - bad Has anyone encountered this weird behaviour? I cannot find a solution anywhere.

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• Looking for Info on a Javascript Testing framework

  - by DaveDev

  Hi Can somebody fill me in on JavaScript Testing Frameworks? I'm working on a project now and as the JS (Mostly jQuery) libraries grow, it's getting more and more difficult to introduce change or refactor, because I have no way of guaranteeing the accuracy of the code without manually testing everything. I don't really know anything about JavaScript Testing Frameworks, or how they integrate/operate in a .Net project, so I thought I'd ask here. What would a good testing framework be for .Net? What does a JavaScript test look like? (e.g. with NUnit, I have [TestFixture] classes & [Test] methods in a ProjectTests assembly) How do I run a javascript test? What are the conceptual differences between testing JS & testing C#? Is there anything else that would be worth knowing? Thanks Dave

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• How do I make a background thread in Java that allows the main application to exit completely? This

  - by Bob

  I have a Java application that creates a new thread to do some work. I can launch the new thread with no problems. When the "main" program terminates, I want the thread I created to keep running - which it does... But the problem is, when I run the main application from Eclipse or from Ant under Windows, control doesn't return unless the background process is killed. If I fork the main java process in ant, I want control to return to ant once the main thread is done with its work... But as it is, ant continues to wait until both the main process and the created thread are both terminated. How do I launch the thread in the background such that control will return to ant when the "main" application is finished? (By the way, when I run the same application under Linux, I am able to do this with no problems).

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• Have you ever derived a programming solution from nature?

  - by Ryu

  When you step back and look at ... the nature of animals, insects, plants and the problems they have organically solved perhaps even the nature and balance of the universe Have you ever been able to solve a problem by deriving an approach from nature? I've heard of Ant Colony Algorithms being able to optimize supply chain amongst other things. Also Fractal's being the "geometry of nature" have been applied to a wide range of problems. Now that spring is here again and the world is coming back to life I'm wondering if anybody has some experiences they can share. Thanks PS I would recommend watching the "Hunting the Hidden Dimension" Nova episode on fractals.

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• CVS in cmd/gui works only the third time I run a command.

  - by Somebody still uses you MS-DOS

  I'm using CVS in the command line. I'm in my repository folder. When I call a CVS command, I get... cvs [log aborted]: unrecognized auth response from localhost: -f [pserver aborted]: /opt/cvs/XXXXXX: no such repository ...2 times. The third time I run the command, it works with no problems. I tried to use a GUI client (CrossVC) and the same problem occurs. I tried inside gVim and Vim using VCSCommand and I'm having the same issues as well. I've tested with different times between each command, but I still have the same problems. I'm using a CVS configuration with stunnel. Why am I having problem with this setup? Why every time just the third time that I try to run the command that actually works?

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• How to handle recurring execution?

  - by ShaneC

  I am trying to validate the solution I came up for what I think is a fairly typical problem. I have a service running and every 10 minutes it should do something. I've ended up with the following: private bool isRunning = true; public void Execute() { while(isRunning) { if(isRunning) { DoSomething(); m_AutoResetEvent.WaitOne(new Timespan(0, 10, 0)); } } } public void Stop() { isRunning = false; m_AutoResetEvent.Set(); } The immediate potential problems I can see is that I'm not doing any sort of locking around the isRunning modification in Stop() which gets called by another thread but I'm not sure I really need to? The worst that I think could happen is that it runs one extra cycle. Beyond that are there any obvious problems with this code? Is there a better way to solve this problem that I'm unaware of?

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• APC not recommended for production?

  - by solomongaby

  I have started having problems with my VPS in the way that it would faill to serve the pages on all the websites. It just showed a blank page, or offered to download the php file ( luckily the code was not in the download file :) ). The server was still running, but this seemed to be a problem with PHP, since i could login into WHM. If i did a apache restart, the sites would work again. After some talks with the server support they told me this is a problem with the APC extension witch they considered to be old and not recommended for production servers. So they removed it for now, to see if the same kind of fails would continue to appear. I haven't read anywhere that APC could have some problems or that its not always recommended to use, quite the contrary ... everywhere people are saying to always use it. The APC extension was installed ssh and is the latest version. Edit: They also dont recomend MemCache and say that a more reliable extension would be eAccelerator

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• PHP, PEAR, and oci8 configuration

  - by zack_falcon

  I'll make this quick. I installed Oracle 11g (with appropriate database, users, etc), Apache 2.4.6, and PHP 5.5.4 on a Fedora 19 system. I wanted to connect PHP to Oracle. What I really wanted to do was to download MDB2_Driver_oci8, which I thought would be easy, but before I can do such a thing, PHP needs to have that plug-in enabled, so here's what I did: Tried to install oci8 via the following: pecl install oci8 When that didn't exactly work the first few times, I figured out I, for some reason, needed "Development tools" - via yum groupinstall "Development Tools" Then I figured out later that PHP actually doesn't do oci8 - it's PHP Devel. So, I had to install that too, via yum install php-devel. And then, I finally got to install oci8. It asked for the Oracle Directory, and that was that. But it said the following: Configuration option 'php_ini' is not set to php.ini location You should add 'extensions=oci8.so' to php.ini First, I did a locate oci8.so - found it in /usr/lib64/php/modules/ Second, I added what it told me to, to the php.ini file. Third, I checked the usual php_info() test page - no mention of OCI8. Uh-oh. Fourth, running both php -i and php -m listed oci8 as one of the modules. Weird. In desperation, I went ahead and downloaded the MDB2_Driver_oci8. Maybe that will fix things. Nope. When I loaded my PHP Webpage, it returned the following: Error message: extension oci8 is not compiled into PHP As well as: MDB2 error: not found Strange. And then I decided to check the error logs: PHP Startup - unable to load dynamic library '/usr/lib64/php/modules/oci8.so' - libclntsh.so.11.1: cannot open shared object file: No such file or directory in Unknown on line 0 And now I'm stuck. I tried going into the php.ini, and found that the extension_dir was commented out. I put it back in, which only seemed to break stuff. Things of note: I followed this (link) guide on how to configure PHP and install oci8. ./configure --with-oci8 doesn't work. Fedora says no such directory. As both the webpage files and the actual server reside on the same PC, I did not install the Oracle Client files. The extension_dir is commented out by default in the php.ini. This is just one of my problems in a long line of problems concerning the replication of an already existing and working, but dying, setup. It seems whenever I want to solve a problem, I have to do X first. And by doing X, I uncover another problem, which I have to solve by doing Y, which has its own problems, etc, etc. Any help would be much appreciated. Thanks.

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• Making Django ignore string literals

  - by James

  UPDATE: It turns out this is a deeper question than I thought at first glance - the issue is that python is replacing the string literals before they ever get to django. I will do more investigating and update this if I find a solution. I'm using django to work with LaTeX templates for report generation, and am running into a lot of problems with the way Django replaces parts of strings. Specficially, I've run into two problems where I try to insert a variable containing latex code. The first was that it would replace HTML characters, such as the less than symbol, with their HTML codes, which are of course gibberish to a LaTeX interpreter. I fixed this by setting the context to never autoescape, like so: c = Context(inputs) c.autoescape = False However, I still have my second issue, which is that Django replaces string literals with their corresponding characers, so a double backslash becomes \, and \b becomes a backspace. How can I force Django to leave these characters in place, so inputs['variable'] = '{\bf this is code} \\' won't get mangled when I use {{variable}} to reference it in the django template?

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• Why does XCode keep downloading old deleted profiles and duplicates of the same profile?

  - by Piepants

  If I refresh the profiles in XCode it: a) Pulls down ones that no longer exist. Profiles that have been deleted from the portal and are no longer there b) Pulls down multiple copies of the same profile. If I add a new device and then update the profiles to include that new device. Then XCode will pull down the new updated profile but also the same profile with an older date (even though the portal only shows one, the latest). If I delete them them XCode they re-appear. I'm having problems getting push notifications to work with an ad-hoc distrubtion and so want to ensure I am build with the latest profiles. This behaviour of XCode is irritating at least, and possibly the source of my problems at worst.

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• Efficiently remove points with same slope

  - by Ram

  Hi, In one of mine applications I am dealing with graphics objects. I am using open source GPC library to clip/merge two shapes. To improve accuracy I am sampling (adding multiple points between two edges) existing shapes. But before displaying back the merged shape I need to remove all the points between two edges. But I am not able to find an efficient algorithm that will remove all points between two edges which has same slope with minimum CPU utilization. Currently all points are of type PointF Any pointer on this will be a great help.

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• Tomcat servlet-api.jar problem

  - by CitadelCSCadet

  I am running a web application using Tomcat and Java Servlets, JSP's, etc. I am aware that in order to use Servlets, it is dependent on the Servlet-api.jar file. Initially I placed this jar file in the WEB-INF/lib/ directory. This has worked fine for me for months during the developmental phase. When we put the application onto the server space we are using, we started seeing wierd problems showing up in the Catalina.out file telling us that there was dependency problems with the servlet-api.jar file. I am aware that tomcat has this jar file in its container, and that I should remove it from the WEB-INF/lib/ directory. I have tried this and it does not work. What do I have to do when I remove this jar file from the local files and allow it to depend on tomcats servlet-api.jar file.

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• Google Pie Chart and Bar Chart (both Interactive) not showing labels.

  - by iRubens

  I'm trying to put Google's BarChart and PieChart both the client side version, and i'm experiencing some problems with the labels over the pie and the labels on the left of the vertical axis (of the bar chart). I checked the code a lot of times and it seems to be like that you can see in the examples. I've tried the same page on Firefox and Chrome and it shows the labels without problems. If i try the examples on IE8 the labels are shown but not in my page. Sincerely I've not any idea where to start to fix this thing. Someone can help me or give me an advice? Thanks in advance.

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• Dynamic Programming resources in C?

  - by EsotericMe

  Hi everyone, I'll be writing the online Google test tomorrow as a fresher. Apparently, they definitely ask one problem on Dynamic Programming? Does anyone know of a good resource for collection of DP problems in C along with solutions? I know what DP is & have used it on an occasion or twice. However I feel to crack a DP problem in test, prior practice of typical problems will make it easier to approach. Any good resources or problem sets with solutions in C will be highly appreciated. Thanks.

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• Is there a font that can't be recognised by an OCR?

  - by user1820564

  I am trying to write a document that can only be read by humans. The document content can't be copied. For that purpose, I am converting its pages to pictures and adding them back to a PDF file. The main issue is that any OCR program can get back the whole written text, especially that the page is going to be clear (as opposed to a scanned book) which will increase the OCR accuracy. So, is there a font that can't be recognized by an OCR. Otherwise, is there a technique that will make my document only readable by humans, yet unrecognised by an OCR? (for instance, adding a specific background, etc...) Thank you in advance.

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