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Articles indexed Saturday May 22 2010

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  • Ruby ways to authenticate using headers?

    - by webdestroya
    I am designing an API system in Ruby-on-Rails, and I want to be able to log queries and authenticate users. However, I do not have a traditional login system, I want to use an APIkey and a signature that users can submit in the HTTP headers in the request. (Similar to how Amazon's services work) Instead of requesting /users/12345/photos/create I want to be able to request /photos/create and submit a header that says X-APIKey: 12345 and then validate the request with a signature. Are there any gems that can be adapted to do that? Or better yet, any gems that do this without adaptation? Or do you feel that it would be wiser to just have them send the API key in each request using the POST/GET vars?

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  • Mathematics for AI/Machine learning ?

    - by Ankur Gupta
    I intend to build a simple recommendation systems for fun. I read a little on the net and figured being good at math would enable on to build a good recommendation system. My math skills are not good. I am willing to put considerable efforts and time in learning maths. Can you please tell me what mathematics topics should I cover? Also if any of you folks can point me to some online material to learn from it would be great. I am aware of MIT OCW, book like collective intelligence. Math Topics to cover and from where to read would really help.

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  • Heuristic for sliding tile problem.

    - by MustDash
    The idea is to move all of the right elements into the left and the left into the right with an empty space in the middle. The elements can either jump over one or two pieces into an empty space. LLL[ ]RRR I'm trying to think of a heuristic for this task. Is the heuristic meant to aid in finding a possible solution, or actually return a number of moves as the solution? How would I express such a heuristic?

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  • How can I use rsync with a FAT file system?

    - by Kim
    I would like to write a simple backup script that saves some data to a FAT drive. Should I reformat the drive and use a better file system or is it possible to use rsync with FAT? If so, what problems might I run into? Would performance be a lot worse? EDIT: This is on linux, didn't even know there was a rsync for windows. The sources are various file systems (it's a mess), and the destination is currently formatted with FAT32. Thank you for your answers, I'll probably go for a reformat, since I'm not completely sure about the file sizes we'll have.

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  • Firefox crash on first load on Ubuntu Linux on Windows Laptop

    - by Ira Baxter
    I've had a Dell Latitude laptop since about 2000 without managing to destroy it. A month ago the Windows 2000 system on it did something stupid to its file system and Windows was completely lost. No point in reinstalling Windows 2000, so I installed an Ubuntu Linux on the laptop. Everything seems normal (installed, rebooted, I can log in, run GnuChess, poke about). ... but ... when I attempt to launch Firefox from the top bar menu icon, I get a bunch of disk activity, the whirling cursor icon goes round a bit and then everything stops: disk, icon, mouse. Literally nothing happens for 5 minutes. Ubuntu is dead, as far as I can tell. A reboot, and I can repeat this reliably. So on the face of it, everything works but Firefox. That seems really strange. The only odd thing about this system when Firefox is booting is that while it has an Ethernet port (that worked fine under Windows), it isn't actually plugged into an Ethernet. As this is the first Firefox boot since the Ubuntu install, maybe Firefox mishandles Internet access? Why would that crash Ubuntu? (I need to go try the obvious experiment of plugging it in).

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  • How do I create two mutual producer/consumers with internal state in Haskell?

    - by Keith
    I've got an agent that takes in states and returns actions, while keeping an internal representation of the utility of state/action pairs. I've also got an environment that takes in actions and returns state/reward pairs. I need to be able to set the agent up with a start state and then continuously go from agent -(action)- environment -(state, reward)- agent -(action)-... However, the internal states (which need to be updated every iteration) need to stay private (that is, within the agent or the environment). This means that I can't simply call environment as a function within the agent using state and action as arguments. I'm somewhat of a Haskell noobie, so I'm not even sure if this is possible.

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  • How can I encode four unsigned bytes (0-255) to a float and back again using HLSL?

    - by Statement
    Hello! I am facing a task where one of my hlsl shaders require multiple texture lookups per pixel. My 2d textures are fixed to 256*256, so two bytes should be sufficient to address any given texel given this constraint. My idea is then to put two xy-coordinates in each float, giving me eight xy-coordinates in pixel space when packed in a Vector4 format image. These eight coordinates are then used to sample another texture(s). The reason for doing this is to save graphics memory and an attempt to optimize processing time, since then I don't require multiple texture lookups. By the way: Does anyone know if encoding/decoding 16 bytes from/to 4 floats using 1 sampling is slower than 4 samplings with unencoded data?

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  • CMS just for backend

    - by krumiro79
    I'm looking for a CMS just for backend that lets you manage database tables with custom fields. I found Wordpress Pods similar to what I'm looking for, but I don't want Wordpress to manage my frontend (and Wordpress Pods don't look professional to me...) Is there something like this out there? Thank you. Sergio

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  • Graph - strongly connected components

    - by HardCoder1986
    Hello! Is there any fast way to determine the size of the largest strongly connected component in a graph? I mean, like, the obvious approach would mean determining every SCC (could be done using two DFS calls, I suppose) and then looping through them and taking the maximum. I'm pretty sure there has to be some better approach if I only need to have the size of that component and only the largest one, but I can't think of a good solution. Any ideas? Thanks.

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  • Good implementations of reinforced learning?

    - by Paperino
    For an ai-class project I need to implement a reinforcement learning algorithm which beats a simple game of tetris. The game is written in Java and we have the source code. I know the basics of reinforcement learning theory but was wondering if anyone in the SO community had hands on experience with this type of thing. What would your recommended readings be for an implementation of reinforced learning in a tetris game? Are there any good open source projects that accomplish similar things that would be worth checking out? Thanks in advanced Edit: The more specific the better, but general resources about the subject are welcomed. Follow up: Thought it would be nice if I posted a followup. Here's the solution (code and writeup) I ended up with for any future students :). Paper / Code

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  • Continue Drupal processing after page send.

    - by David
    I need to do some additional processing after a Drupal page has been sent. I know I could fire a background shell command, but I need the current Drupal execution context to be maintained. I've spent a lot of time looking, but I can't find any documentation in this regard. This is surprising because it must surely be a common requirement. The only real idea I have is to fire up Drupal (again) via a shell command (exec, etc) and supply it with a pseudo path which would invoke the continued processing. But this seems unnecessarily complex/wasteful. Any pointers greatly appreciated, tks.

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  • how to make PHP lists all Linux Users?

    - by Data-Base
    Hello I want to build a php based site that (automate) some commands on my Ubuntu Server first thing I did was going to the file (sudoers) and add the user www-data so I can execute php commands with root privileges! # running the web apps with root power!!! www-data ALL=(ALL) NOPASSWD: ALL then my PHP code was <?php $command = "cat /etc/passwd | cut -d\":\" -f1"; echo 'running the command: <b>'.$command."</b><br />"; echo exec($command); ?> it returns only one user (the last user) !!! how to make it return all users? thank you

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  • Is it possible to "learn" a regular expression by user-provided examples?

    - by DR
    Is it possible to "learn" a regular expression by user-provided examples? To clarify: I do not want to learn regular expressions. I want to create a program which "learns" a regular expression from examples which are interactively provided by a user, perhaps by selecting parts from a text or selecting begin or end markers. Is it possible? Are there algorithms, keywords, etc. which I can Google for? EDIT: Thank you for the answers, but I'm not interested in tools which provide this feature. I'm looking for theoretical information, like papers, tutorials, source code, names of algorithms, so I can create something for myself.

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  • Project generation problem using Spring Roo

    - by Harry
    Hi, I just downloaded SpringSource Tool Suite, and tried to generate a demo application using roo, but i'm getting error below Code: Created /home/dev/springsource/workspace/demo/pom.xml Undo create /home/dev/springsource/workspace/demo/pom.xml Invalid dependency scope: PROVIDED [Timer-0] NullPointerException at org.springframework.roo.classpath.itd.AbstractItdMetadataProvider.notify(AbstractItdMetadataProvider.java:84) What is the problem? is this Maven issue? Using: Ubuntu 8.10, SpringSource Tool Suite Version: 2.3.3.M1, Roo 1.1.0.M1, Apache Maven Thanks

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  • Firefox crash on first load on Ubuntu Linux on older Dell Laptop

    - by Ira Baxter
    I've had a Dell Latitude laptop since about 2000 without managing to destroy it. A month ago the Windows 2000 system on it did something stupid to its file system and Windows was completely lost. No point in reinstalling Windows 2000, so I installed an Ubuntu Linux on the laptop. Everything seems normal (installed, rebooted, I can log in, run GnuChess, poke about). ... but ... when I attempt to launch Firefox from the top bar menu icon, I get a bunch of disk activity, the whirling cursor icon goes round a bit and then everything stops: disk, icon, mouse. Literally nothing happens for 5 minutes. Ubuntu is dead, as far as I can tell. A reboot, and I can repeat this reliably. So on the face of it, everything works but Firefox. That seems really strange. The only odd thing about this system when Firefox is booting is that while it has an Ethernet port (that worked fine under Windows), it isn't actually plugged into an Ethernet. As this is the first Firefox boot since the Ubuntu install, maybe Firefox mishandles Internet access? Why would that crash Ubuntu? (I need to go try the obvious experiment of plugging it in).

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  • Is F# a good language for card game AI?

    - by Anthony Brien
    I'm writing a Mahjong Game in C# (the Chinese traditional game, not the solitaire kind). While writing the code for the bot player's AI, I'm wondering if a functional language like F# would be a more suitable language than what I currently use which is C# with a lot of Linq. I don't know much about F# which is why I ask here. To illustrate what I try to solve, here's a quick summary of Mahjong: Mahjong plays a bit like Gin Rummy. You have 13 tiles in your hand, and each turn, you draw a tile and discard another one, trying to improve your hand towards a winning Mahjong hand, which consists or 4 sets and a pair. Sets can be a 3 of a kind (pungs), 4 of a kind (kongs) or a sequence of 3 consecutive tiles (chows). You can also steal another player's discard, if it can complete one of your sets. The code I had to write to detect if the bot can declare 3 consecutive tiles set (chow) is pretty tedious. I have to find all the unique tiles in the hand, and then start checking if there's a sequence of 3 tiles that contain that one in the hand. Detecting if the bot can go Mahjong is even more complicated since it's a combination of detecting if there's 4 sets and a pair in his hand. And that's just a standard Mahjong hand. There's also numerous "special" hands that break those rules but are still a Mahjong hand. For example, "13 unique wonders" consists of 13 specific tiles, "Jade Empire" consists of only tiles colored green, etc. In a perfect world, I'd love to be able to just state the 'rules' of Mahjong, and have the language be able to match a set of 13 tiles against those rules to retrieve which rules it fulfills, for example, checking if it's a Mahjong hand or if it includes a 4 of a kind. Is this something F#'s pattern matching feature can help solve?

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