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• initial conditions in coupled systems

  - by Alireza

  how should i write the initial conditions and solve two coupled differential equation? for ex. like: s1 := diff(n[D](t), t) = a-b*n[D](t)^2-c*n[D](t)-e*n[D](t)*n[T](t) s2 := diff(n[T](t), t) = b*n[D](t)^2-c*n[D](t)-e*n[D](t)*n[T](t) dsolve({s1, s2});

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• Creating a child process on Unix systems?

  - by Hakan Svensson

  I'm trying to create a child process in another process. I am writing both the programs in C language. First I write a dummy process which will be the child process. What it is doing is only to write a string on the screen. It works well on its own. Then I write another program which will be the parent process. However, I can't make it happen. I'm trying to use fork and execl functions together, but I fail. I also want the child process does not terminate until the parent process terminates. How should I write the parent process? Thanks.

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• operating systems - TLBs

  - by stabGreeol

  I'm trying to get my head round this (okay, tbh cramming a night before the exams :) but i can't figure out (nor find a good high level overview on the net) of this: 'page table entries can be mapped to more than one TLB entry.. if for example every page table entry is mappped to two TLB entries, this is know as 2-way set associative TLB' My question is, why would we want to map this more than once? surely we want to have the maximum number of possible entries represented in the TLB, and duplication would waste space right ? What am i missing? Many thanks

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• dev and prod systems in rails

  - by poseid

  What exactly is the difference in rails between dev and prod environments. When I develop an application in dev mode, do I have peformance problems, or others if I clone my dev environment on prod?

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• Why Java Swing behaves different on different systems?

  - by Tom Brito

  Some swing code I write in my computer behave different on my colleague's computer, and in my PC, and in my notebook. I wonder, is there something I can do to my Swing applications behave the same in every computer? I want to have sure a algorithm I've tested in my computer will work the same way in my clients computers. E.g. Problem to focus JTextField

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• Reasonable expectation to support new Operating Systems?

  - by Neil N

  My company has a desktop app originally developed for Windows XP. The original programmer has since been fired (fired with extreme prejudice I might add). I have fixed the app various times but overall try to avoid it, it is a mess and the only real way to fix it is to completely rewrite it, which could take a year. We have been trying to "forget" about this app, and instead steer clients towards our web version, which is more up to date, easier to maintain, easier to extend, and WAY easier to support. Most clients agree, the web version is just better all around. However we have one client that insists on using the desktop app. The app required a little duct tape to get working on Vista, but now completely breaks on Windows 7. I'm not even sure WHAT all the fixes are to get it working on Win7 (the current time estimate stands at "miracle") but after both installing the RELEASE build, and running the DEBUG build from Visual Studio, the app has errors on nearly every user action, and from what I can see from a high level test run, none of them are related. Since Windows 7 did not exist when this app was developed, is my company really expected to make all the required changes to make it function as "smoothly" as it did on XP?

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• Web-Frameworks for Education Management Systems?

  - by Indebi

  So, I'm working on an idea and I'll go into a brief overview of that but my question is, What are some good web frameworks for this situation? I have some experience in the following languages: C# Python I have considerably more experience in C# than Python, however I am expecting to learn new things. My idea is this, a completely web-based community-oriented Education Management System that focuses on making students and teachers day-to-day lives easier. For students it will provide a centralized place for them to do homework, study for tests, and reinforce concepts learned previously in class. For teachers it will give them a centralized place to handle assignments, attendance, homework, tests, and all other major parts of classroom management. All of that, but in a community-oriented fashion. Everything a teacher does is shared and open to constructive criticism, allowing other teachers to use their assignments/tests and for students or other teachers to comment, rate and criticize their assignments. This encourages an environment of openness that will allow teacher's to focus on teaching and student's to focus on learning. And that community wouldn't be limited to one school or school-district, this system would be completely school-independent. Please note that I have no problem with hearing constructive criticism on this idea, however I would prefer if this post was more focused on my question. I have somewhat explored about the following options: Django ASP.NET Ruby on Rails Silverlight (1) I have Django installed and I played with it for a little bit, I really like how easy setting up databases are and how it handles the database completely for you. I don't really know how to use it very well and I don't quite understand the Model-View-Controller paradigm(?) for it yet but I haven't thought about it much. I also like the fact that it uses Python. (2) I don't really like Visual Studio for developing in ASP.NET, I hate the way the web-designer works and it just feels clunky and old. I like the server-side development part though. I don't like how expensive ASP.NET and overall Visual Studio is, even if I do get it for free for now using DreamSpark (3) I haven't been able to explore much with this, I could not get Rails (or maybe Ruby) properly installed. I first installed it within RadRails and that didn't work so I uninstalled RadRails and then installed the latest version of Ruby off the official Windows Installer and then installed Ruby on Rails through gem and even after all that it still didn't work, so I installed Netbeans and attempted to use it there but it still did not work (4) I like Silverlight in some extents, I've played with this one the most, it's very similar to WPF (which I've used the most) in a lot of ways but I don't like how database connectivity works, at least in comparison to Django. I also dislike how expensive everything with Microsoft is, even if I get it for free for now with DreamSpark. I would like to hear some suggestions from experienced web-developers as to what I should use and why, or at least what some good options are for my scenario Your help would be very appreciated

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• recommendation systems and the cold start problem

  - by Hellnar

  Hello, I am curious what are the methods / approaches to overcome the "cold start" problem where when a new user or an item enters the system, due to lack of info about this new entity, making recommendation is a problem. I can think of doing some prediction based recommendation (like gender, nationality and so on). Thanks

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• Qt : Nokia proposera démos et conférence lors du rts EMBEDDED SYSTEMS de Paris du 30 au 31 Mars proc

  Nokia proposera des démos de Qt lors du rts EMBEDDED SYSTEMS Du 30 au 31 Mars à la Porte de Versailles Nokia sera présent lors du rts EMBEDDED SYSTEMS, 18ème édition du salon des Solutions informatiques temps-réel et systèmes embarqués. Sur son stand (#A20) le constructeur proposera des démos de Qt et le mercredi 31 mars, à 13h, Thierry Bastian, Software Engineer, tiendra une conférence pour présenter le framework multi-plateformes. La manifestation se tiendra à la Porte de Versailles à Paris. Plus d'informations et les modalités pour s'inscrire sur cette page....

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• Qt : Nokia proposera démos et conférence lors du rts EMBEDDED SYSTEMS de Paris du 30 au 31 Mars proc

  Nokia proposera des démos de Qt lors du rts EMBEDDED SYSTEMS Du 30 au 31 Mars à la Porte de Versailles Nokia sera présent lors du rts EMBEDDED SYSTEMS, 18ème édition du salon des Solutions informatiques temps-réel et systèmes embarqués. Sur son stand (#A20) le constructeur proposera des démos de Qt et le mercredi 31 mars, à 13h, Thierry Bastian, Software Engineer, tiendra une conférence pour présenter le framework multi-plateformes. La manifestation se tiendra à la Porte de Versailles à Paris. Plus d'informations et les modalités pour s'inscrire sur cette page....

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• Open GL ES 2.0 co-ordinate systems

  - by Chris

  Hi, I want to use Open GL ES 2.0 for a new game, but I have two questions. Q: The first is how do I set up perspective views in Open GL ES 2.0 - do I need to include Open GL ES 1.0 and use glOrtho, or is there a new way? Q: I want to use the 4th quadrant of a Cartesian co-ordinate system for my game and not use -0.5 to +0.5 for values on screen, how once the first question is answered can I achieve this? Other resources: http://iphonedevelopment.blogspot.com/2009/04/opengl-es-from-ground-up-part-3.html Thanks Chris

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• Books on hexadecimal and binary systems

  - by MDK

  I have a basic understanding of hexadecimal and binary representations, which I'd like to improve. Can anyone recommend books that can help me along? Thanks.

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• Systems design question: DB connection management in load-balanced n-tier

  - by aoven

  I'm wondering about the best approach to designing a DB connection manager for a load-balanced n-tier system. Classic n-tier looks like this: Client -> BusinessServer -> DBServer A load-balancing solution as I see it would then look like this: +--> ... +--+ +--> BusinessServer +--+--> SessionServer --+ Client -> Gateway --+--> BusinessServer +--| +--> DBServer +--> BusinessServer +--+--------------------+ +--> ... +--+ As pictured, the business server component is being load-balanced via multiple instances, and a hardware gateway is distributing the load among them. Session server probably needs to be situated outside the load-balancing array, because it manages state, which mustn't be duplicated. Barring any major errors in design so far, what is the best way to implement DB connection management? I've come up with a couple of options, but there may be others I'm not aware of: Introduce a new Broker component between the DBServer and the other components and let it handle the DB connections. The upside is that all the connections can be managed from a single point, which is very convenient. The downside is that now there is an additional "single point of failure" in the system. Other components must go through it for every request that involves DB in some way, which also makes this a bottleneck. Move the DB connection management into BusinessServer and SessionServer components and let each handle its own DB connections. The upside is that there is no additional "single point of failure" or bottleneck components. The downside is that there is also no control over possible conflicts and deadlocks apart from what DBServer itself can provide. What else can be done? FWIW: Technology is .NET, but none of the vendor-specific stacks are used (e.g. no WCF, MSMQ or the like).

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• Sex appear of computer graphics: movie like UI systems

  - by anon

  It's well know that 1) the way computers actually work 2) the way computers are protrayed in movies are not the same. In particular (2) looks much much cooler than (1). Where can I learn more about making flashy, superficially useful but deepdown useless fancy graphics UIs like that? It's almost in the realm of "hollywood special effects" -- like fire/smoke/fire, but I don't want natural phenomenon; I want user interfaces. Concrete question: where can I learn about creating flashy, cool looking (though not necessairly useful) user interfaces? [Perferably in OpenGL]

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• Receiving UDP broadcasts on multihomed systems

  - by theller

  I have a Windows XP machine with more than one network adapter. When I receive a UDP broadcast package from another machine that does not yet have a valid IP address, howcan I determine which network adapter received this package? I need to implement a kind on custom DHCP server...

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• Free Testing / Code Coverage systems for C++

  - by Billy ONeal

  I'd like to start using a Test Driven Development system for a private project since I saw my employer using it and realized it was very useful. My employer's project was in C# but mines are in C and C++. I looked around and saw that several packages exist for both Java and .NET (for example: NCover, NUnit, ...). Unfortunately I found it difficult to find good C++ testing frameworks. Do you know of any unit testing frameworks that satisfy the following requirements? IMPORTANT: Must provide code coverage statistics, as I'd like to have some idea of how well my tests cover my code-base. Must be free Usable with C++ projects EDIT: To be clear, I know of many existing unit test frameworks. The code coverage piece is what's most important.

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• Developing Qt applications in Unix systems using Qt Creator

  - by Jake Petroules

  I'm developing a Qt application in Linux using Qt Creator (2.1 RC). I've created 2 projects, and used the wizard to add the library project to the application project. However when I run it, I receive the error: /home/jakepetroules/silverlock/silverlock-build-desktop/desktop/silverlock: error while loading shared libraries: libsilverlocklib.so.1: cannot open shared object file: No such file or directory Is there some qmake variable I can set so that Qt Creator will set up the environment properly to run? It's quite annoying to have to copy all the files to another directory with a launcher script just to be able to test the build. On Windows it works perfectly - Qt Creator automatically adds the directories containing the DLLs to the PATH when it runs your application (where running it from Explorer would say DLL not found). Mac OS X is even worse, having to run install_name_tool on everything... So how can I set up my qmake files so everything works right from the run button in Qt Creator? Kind of hard to debug without this ability, too.

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• How Google Web Starter Kit serves adaptive image for mobile?

  - by 5argon

  My website weirdly (in a good way) serves smaller images when viewed on mobile. I wanted to know what cause this? As far as I know this is not the default behaviour, so I think it must be Google Web Starter Kit's doing.Here is the debug information when debugging on device. All images became 231 B size no matter how large it actually is. (On desktop debugging the size varies.) I tried using Google Web Starter Kit (https://github.com/google/web-starter-kit) recently. The tools in it are made of Ruby, Node.js, SASS and Gulp to help you 'build' website. Pre-build you can enjoy automatic reload because the Gulp script will watch all files for you. When build it will run various tools to minify HTML,CSS and compress images. According to this page https://developers.google.com/web/fundamentals/tools/build/build_site the gulp-imagemin was used. So I guess the imagemin is doing the mobile optimization for me? What kind of compression can serve automatically resized image on mobile? And why is the size 231 B? Is this related to my screen size?

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• update available status when systems goes crash

  - by Bharanikumar

  Hi , i am doing one small application , wheich have login functionality, in the user table am maintaining the AVAILABLE status for the logged USER, example : i have three user called foo1,foo2,foo3 , When foo1 logged then his AVAILABLE STATUS WILL UPDATE AS 1 IN THE USERTABLE, if he logged out then his AVAILABLE STATUS goes to 0, like the foo2, and foo3 , for this available status flasg , amsimply using the update operation ..no other big functionality , Now What i want is, If somthing happened when user logged in , then i want to make the available status as 0, Somthing means , I WANT TO CHANGE THE AVAILABLE STATUS TO 0 , WHEN system CRASH OR browser crash Thanks Bharanikumar

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• What database systems should an startup company consider?

  - by Am

  Right now I'm developing the prototype of a web application that aggregates large number of text entries from a large number of users. This data must be frequently displayed back and often updated. At the moment I store the content inside a MySQL database and use NHibernate ORM layer to interact with the DB. I've got a table defined for users, roles, submissions, tags, notifications and etc. I like this solution because it works well and my code looks nice and sane, but I'm also worried about how MySQL will perform once the size of our database reaches a significant number. I feel that it may struggle performing join operations fast enough. This has made me think about non-relational database system such as MongoDB, CouchDB, Cassandra or Hadoop. Unfortunately I have no experience with either. I've read some good reviews on MongoDB and it looks interesting. I'm happy to spend the time and learn if one turns out to be the way to go. I'd much appreciate any one offering points or issues to consider when going with none relational dbms?

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• Learning about version control systems, Git, SVN

  - by anijhaw

  I am a basic SVN user now trying to learn GIT for a new position. I am trying the usual reading docs and watching videos. However after doing all that I still feel that there is a lot that I do not know. I was wondering if there is a place like project Euler for programming languages, that provides a series of exercises that you can do just to increase your confidence and test your knowledge about a version control system. Something thats generic enough and gets you up to speed with how to do basic things. This could also serve as a comparison point of sorts between multiple VCSs, that would show what things are easy in which VCS. If there is nothing I was planning to document my journey in learning GIT and the create an exercise of this sort.

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• Do all the HTML5 storage systems work together ?

  - by azera

  While there are a lot of good stuff about html5, one thing I don't get is the redondant storage mechanism, first there is localstorage and sessionstorage, which are key value stores, one is for one instance of the app ("one tab"), and the other works for all the instances of that application so they can share data. Both are saved when you close your browser and have a limited size (usually 5MB), that's great and everything would be nice if we stopped there. But then there is the "Web SQL Database", which has the same security system as the localstorage, the same size limit, the same everything except it works like/is sqlite, with tables and sql syntax and all of that. And the bummer is, they don't work on the same data at all ! This is not two way to access your data, this is really two storage for every html 5 app out there (not created by default yes, but still you see my point). What I would like to know is, is there a reason for both of this mechanisms to exist at the same time ? Or did they just look at sql and nosql movement to pick the best then went "screw it let's add both !" ? Why not implement local/session storage as a table inside web sql db ?

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• Sex appeal of computer graphics: movie like UI systems [closed]

  - by anon

  It's well know that 1) the way computers actually work 2) the way computers are protrayed in movies are not the same. In particular (2) looks much much cooler than (1). Where can I learn more about making flashy, superficially useful but deepdown useless fancy graphics UIs like that? It's almost in the realm of "hollywood special effects" -- like fire/smoke/fire, but I don't want natural phenomenon; I want user interfaces. Concrete question: where can I learn about creating flashy, cool looking (though not necessairly useful) user interfaces? [Perferably in OpenGL]

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• What does the "build-essential" Terminal command mean & do in Linux based operating systems like Ubu

  - by Adam Siddhi

  Hi. I am researching how to install Ruby 1.9.1 in Xubuntu 10.04 and I came across the command build-essential multiple times. Sometimes it is followed by packages and sometimes it is both preceded and post-ceded by packages. The 2 examples I am looking at are: sudo apt-get install build-essential zlib1g zlib1g-dev zlibc libruby1.9 libxml2 libxml2-dev libxslt-dev and sudo apt-get install ruby irb ri rdoc ruby1.8-dev libzlib-ruby libyaml-ruby libreadline-ruby libncurses-ruby libcurses-ruby libruby libruby-extras libfcgi-ruby1.8 build-essential libopenssl-ruby libdbm-ruby libdbi-ruby libdbd-sqlite3-ruby sqlite3 libsqlite3-dev libsqlite3-ruby libxml-ruby libxml2-dev Thanks :adam

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• Chrome SSL Security Issue under Windows systems?

  - by fraido

  The Fortify.net website allows you to check what SSL Encryption key is used by your browser. I gave it a try with the browsers I've on my machine and these are the results Fedora 9 Firefox 3.0.8 = AES cipher, 256-bit key Chrome 4.0.249.30 = AES cipher, 256-bit key Windows XP SP3 IE 6.0.2x = RC4 cipher, 128-bit key Firefox = AES cipher, 256-bit key Chrome 4.1.249.1042 (42199) = RC4 cipher, 128-bit key .... WHAT!!?!! Chrome is using RC4 128-bit (as IE6 does) that is well known as been very weak! Chrome under Unix works fine... I'm wondering how is this possible? Do you have this issue or is there a way to change the default key to be AES 256bit? I'm using Chrome as the main browser under Windows and I'm really considering to switch back to Firefox

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