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• Creating a computer with pencil and paper [closed]

  - by Justian Meyer

  This concept has been brought to my attention before, but many people might know it from this popular comic here, where he uses stones instead of points on a paper. This concept is so abstract to me. A full-functioning computer that can manage algorithms, input, output, etc. without electricity? Surely, it's difficult to visualize because my definition of a computer is not exactly what the word sounds like COMPUTE-ER. Can someone help me bring the concept to light - the understanding, how to make one, etc? It seems like it'd be an interesting read, although I think I wouldn't be able to make it do anything. Many thanks in advance for responses. I've tried searching Google, but all I got were ways to diagram code and chart ideas. -.Justian.

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• Direct video card access

  - by icemanind

  Guys, I am trying to write a class in C# that can be used as a direct replacement for the C# Bitmap class. What I want to do instead though is perform all graphic functions done on the bitmap using the power of the video card. From what I understand, functions such as DrawLine or DrawArc or DrawText are primitive functions that use simple cpu math algorithms to perform the job. I, instead, want to use the graphics card cpu and memory to do these and other advanced functions, such as skinning a bitmap (applying a texture) and true transparancy. My problem is, in C#, how do I access direct video functions? Is there a library or something I need?

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• Determine if a string contains only alphanumeric characters (or a space)

  - by dreamlax

  I'm learning C++ and I am writing a function that determines whether a string contains only alphanumeric characters and spaces. I suppose I am effectively testing whether it matches the regular expression ^[[:alnum:] ]+$ but without using regular expressions. I have seen a lot of algorithms revolve around iterators, so I tried to find a solution that made use of iterators, and this is what I have: #include <algorithm> static inline bool is_not_alnum_space(char c) { return !(isalpha(c) || isdigit(c) || (c == ' ')); } bool string_is_valid(const std::string &str) { return find_if(str.begin(), str.end(), is_not_alnum_space) == str.end(); } Is there a better solution, or a “more C++” way to do this?

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• How to create digital signature that can not be used to reproduce the message twice

  - by freediver

  I am creating a client-server application and I'd like to send data from server to client securely. Using public/private key algorithms makes sense and in PHP we can use openssl_sign and openssl_verify functions to check that the data came by someone who has the private key. Now imagine that one of the actions sent by server to client is destructive in nature. If somebody uses an HTTP sniffer to catch this command (which will be signed properly) how can I further protect the communication to ensure that only commands coming from our server get processed by the client? I was thinking about using current UTC time as part of the encrypted data but client time might be off. Is there a simple solution to the problem?

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• Google Suggest - What determines the sort order of suggested queries on google?

  - by John Himmelman

  How is this sort order determined? Is it ranked by popularity, number of results, or a mysterious google algorithm? Does there algorithm take into account the search popularity of a query (using google-trends data or something)? Edit: I found a news article dating back to when google suggest was made public in 2004. Here is an excerpt... How does it work? "Our algorithms use a wide range of information to predict the queries users are most likely to want to see. For example, Google Suggest uses data about the overall popularity of various searches to help rank the refinements it offers." Source: http://www.free-seo-news.com/newsletter138.htm

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• What's the best way to match a query to a set of keywords?

  - by Ryan Detzel

  Pretty much what you would assume Google does. Advertisers come in and big on keywords, lets say "ipod", "ipod nano", "ipod 60GB", "used ipod", etc. Then we have a query, "I want to buy an ipod nano" or "best place to buy used ipods" what kind of algorithms and systems are used to match those queries to the keyword set. I would imagine that some of those keyword sets are huge, 100k keywords made up of one or more actual words. on top of that queries can be 1-n words as well. Any thoughts, links to wikipedia I can start reading? From what I know already I would use some stemmed hash in disk(CDB?) and a bloom filter to check to see if I should even go to disk.

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• What's the most straightforward way to typeset MLA-style college essays in LaTeX?

  - by bcat

  I've been using LaTeX for a little while now to typeset my algorithms homework, and I really like the quality of the output as well as the ease-of-use. I'd like to starting using LaTeX in other classes as well, but non–computer-science subjects have more stringent formatting requirements than I've come across in CS. Most classes that require essays want them to be formatted in MLA style, but I'm not sure what to best way to do that using LaTeX is. I've tried Googling "latex mla" and other similar things, but I've found many different MLA templates, and my LaTeX skills aren't good enough to determine which is the best. Is anyone else using LaTeX for "normal" essays, and, if so, how are you doing it?

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• What should I do to practice?

  - by simion

  I start a year long industrial placement in September where i will be coding in Java predominantly. I am going to use the summer to brush up on my Java as in year one of the degree Java was the main language taught for OOP modules. However this year i have had no Java exposure except for an algorithms module, which was one of eight, so as you can see i am probably getting really rusty!. What i wanted to know is, how does the "real world" java programming differ from university coding and what do you suggest i brush up on that would be different to my normal workings. As a start I definitely need to get familiar with a professional IDE like NetBeans, opposed to having used BlueJ throughout but more specifically what coding practices should I get more familiar with. I appreciate they wont expect me to be a qualified full developer and will give me time, but I would like to hit the ground running as it were, with me having full hopes to secure a permanent position after I finish my degree.

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• Using a locale-dependent sorting function in Ruby/Rails

  - by knuton

  What is a good approach to sorting an array of strings in accordance with the current locale? For example the standard Array#sort puts "Ä" after "Z", which is not correct in German. I would have expected the gem I18n to offer a hook for defining my own sorting algorithms or providing collation strings or objects. In my imagination, passing this proc or string to the sort function, would make it behave as necessary. I know that this is possible in Python, for example. Google has not helped me this time. Can you? Any advice appreciated!

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• Remove from a std::set<shared_ptr<T>> by T*

  - by Autopulated

  I have a set of shared pointers: std::set<boost::shared_ptr<T>> set; And a pointer: T* p; I would like to efficiently remove the element of set equal to p, but I can't do this with any of the members of set, or any of the standard algorithms, since T* is a completely different type to boost::shared_ptr<T>. A few approaches I can think of are: somehow constructing a new shared_ptr from the pointer that won't take ownership of the pointed to memory (ideal solution, but I can't see how to do this) wrapping / re-implementing shared_ptr so that I can do the above just doing my own binary search over the set Help!

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• Problems with dynamic programming

  - by xan

  I've got difficulties with understanding dynamic programming, so I decided to solve some problems. I know basic dynamic algorithms like longest common subsequence, knapsack problem, but I know them because I read them, but I can't come up with something on my own :-( For example we have subsequence of natural numbers. Every number we can take with plus or minus. At the end we take absolute value of this sum. For every subsequence find the lowest possible result. in1: 10 3 5 4; out1: 2 in2: 4 11 5 5 5; out2: 0 in3: 10 50 60 65 90 100; out3: 5 explanation for 3rd: 5 = |10+50+60+65-90-100| what it worse my friend told me that it is simple knapsack problem, but I can't see any knapsack here. Is dynamic programming something difficult or only I have big problems with it?

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• Merging photo textures - (from calibrated cameras) - projected onto geometry

  - by freakTheMighty

  I am looking for papers/algorithms for merging projected textures onto geometry. To be more specific, given a set of fully calibrated cameras/photographs and geometry, how can we define a metric for choosing which photograph should be used to texture a given patch of the geometry. I can think of a few attributes one may seek minimize including the angle between the surface normal and the camera, the distance of the camera from the surface, as well as minimizing some parameterization of sharpness. The question is how do these things get combined and are there well established existing solutions?

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• Standardizing camera input in OpenCV? (Contrast/Saturation/Brightness etc..)

  - by karpathy

  I am building an application using OpenCV that uses the webcam and runs some vision algorithms. I would like to make this application available on the internet after I am done, but I am concerned about the vast differences in camera settings on every computer, and I am worried that the algorithm may break if the settings are too different from mine. Is there any way, after capturing the frame, to post process it and make sure that the contrast is X, brightness is Y, and saturation is Z? I think the Camera settings themselves can not be changed from code directly using the current OpenCV Python bindings. Would anyone be able to tell me about how I could calculate some of these parameters from the image and adjust them appropriately using OpenCV?

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• Programming tutorials for people with zero experience

  - by www.aegisub.net

  A friend of mine is interested in learning how to program computers, but she knows nothing about programming. I suggested that Python might be a good language to start with, but after some googling, I couldn't find any tutorials that covered both programming and Python in an adequate way. I don't want her to go through the tiresome "learn algorithms in pseudocode first" routine. Instead, I'd like a tutorial that will explain the basic ideas while working towards a real goal, e.g. a very simple console game. Does anyone know of any such tutorials? Do you think that I'm mistaken in how I'm handling this? Is Python a bad choice? I know that something like C, C++ or Java won't work - too many details will be very counterproductive. On the other hand, I think that Lisp might be too mathematical and abstract. Python, on the other hand, will let her even do something like coding primitive graphical games in a short period of time.

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• Level of Detail for 3D terrains/models in Mobile Devices (Android / XNA )

  - by afriza

  I am planning to develop for WP7 and Android. What is the better way to display (and traverse) 3D scene/models in term of LoD? The data is planned to be island-wide (Singapore). 1) Real-Time Dynamic Level of Detail Terrain Rendering 2) Discrete LoD 3) Others? And please advice some considerations/algorithms/resources/source codes. something like LoD book also Okay. Side note: I am a beginner in this area but pretty well-versed in C/C++. And I haven't read the LoD book. Related posts: - Distant 3D object rendering [games]

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• Lua: Random: Percentage

  - by jargl

  I'm creating a game and currently have to deal with some math.randomness. As I'm not that strong in Lua, how do you think Can you make an algorithm that uses math.random with a given percentage? I mean a function like this: function randomChance( chance ) -- Magic happens here -- Return either 0 or 1 based on the results of math.random end randomChance( 50 ) -- Like a 50-50 chance of "winning", should result in something like math.random( 1, 2 ) == 1 (?) randomChance(20) -- 20% chance to result in a 1 randomChance(0) -- Result always is 0 However I have no clue how to go on, and I completely suck at algorithms I hope you understood my bad explanation of what I'm trying to accomplish

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• Iterator category

  - by Knowing me knowing you

  In code: //I know that to get this effect (being able to use it with std algorithms) I can inherit like I did in line below: class Iterator //: public std::iterator<std::bidirectional_iterator_tag,T> { private: T** itData_; public: //BUT I WOULD LIKE TO BE ABLE TO DO IT BY HAND AS WELL typedef std::bidirectional_iterator_tag iterator_category; typedef T* value_type;//SHOULD IT BE T AS value_type or T*? typedef std::ptrdiff_t difference_type; typedef T** pointer;//SHOULD IT BE T* AS pointer or T**? typedef T*& reference;//SHOULD IT BE T& AS reference or T*&? }; Basically what I'm asking is if I have my variable of type T** in iterator class is it right assumption that value type for this iterator will be T* and so on as I described in comments in code, right next to relevant lines. Thank you.

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• The easiest way to draw an image?

  - by Benno

  Assume you want to read an image file in a common file format from the hard drive, change the color of one pixel, and display the resulting image to the screen, in C++. Which (open-source) libraries would you recommend to accomplish the above with the least amount of code? Alternatively, which libraries would do the above in the most elegant way possible? A bit of background: I have been reading a lot of computer graphics literature recently, and there are lots of relatively easy, pixel-based algorithms which I'd like to implement. However, while the algorithm itself would usually be straightforward to implement, the necessary amount of frame-work to manipulate an image on a per-pixel basis and display the result stopped me from doing it.

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• Secure password transmission over unencrypted tcp/ip

  - by academicRobot

  I'm in the designing stages of a custom tcp/ip protocol for mobile client-server communication. When not required (data is not sensitive), I'd like to avoid using SSL for overhead reasons (both in handshake latency and conserving cycles). My question is, what is the best practices way of transmitting authentication information over an unencrypted connection? Currently, I'm liking SRP or J-PAKE (they generate secure session tokens, are hash/salt friendly, and allow kicking into TLS when necessary), which I believe are both implemented in OpenSSL. However, I am a bit wary since I don't see many people using these algorithms for this purpose. Would also appreciate pointers to any materials discussing this topic in general, since I had trouble finding any.

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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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• How does Photoshop (Or drawing programs) blit?

  - by user146780

  I'm getting ready to make a drawing application in Windows. I'm just wondering, do drawing programs have a memory bitmap which they lock, then set each pixel, then blit? I don't understand how Photoshop can move entire layers without lag or flicker without using hardware acceleration. Also in a program like Expression Design, I could have 200 shapes and move them around all at once with no lag. I'm really wondering how this can be done without GPU help. I don't think super efficient algorithms could justify that? Thanks

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• "Did you mean" feature on a dictionary database

  - by Hazar

  I have a ~300.000 row table; which includes technical terms; queried using PHP and MySQL + FULLTEXT indexes. But when I searching a wrong typed term; for example "hyperpext"; naturally giving no results. I need to "compansate" little writing errors and getting nearest record from database. How I can accomplish such feaure? I know (actually, learned today) about Levenshtein distance, Soundex and Metaphone algorithms but currently not having a solid idea to implement this to querying against database. Best regards. (Sorry about my poor English, I'm trying to do my best)

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• O(log N) == O(1) - Why not?

  - by phoku

  Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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• Framework/tool for processing C++ unit tests with numerical output

  - by David Claridge

  Hi, I am working on a C++ application that uses computer vision techniques to identify various types of objects in a sequence of images. The (1000+) images have been hand-classified, so we have an XML file for each image containing a description of where the objects are actually located in the images. I would like to know if there is a testing framework that can understand/graph results from tests that are numeric, in this case some measure of the error in the program's classification of the images, rather than just pass/fail style unit tests. We would like to use something like CDash/CTest for running these automated tests, and viewing over time how improvements to the vision algorithms are causing the images to be more correctly classified. Does anyone know of a tool/framework that can do this?

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• How to protect against GHC7 compiled programs taking all memory?

  - by Petr Pudlák

  When playing with various algorithms in Haskell it often happens to me that I create a program with a memory leak, as it often happens with lazy evaluation. The program taking all the memory isn't really fun, I often have difficulty killing it if I realize it too late. When using GHC6 I simply had export GHCRTS='-M384m' in my .bashrc. But in GHC7 they added a security measure that unless a program is compiled with -rtsopts, it simply fails when it is given any RTS option either on a command line argument or in GHCRTS. Unfortunately, almost no Haskell programs are compiled with this flag, so setting this variable makes everything to fail (as I discovered in After upgrading to GHC7, all programs suddenly fail saying "Most RTS options are disabled. Link with -rtsopts to enable them."). Any ideas how to make any use of GHCRTS with GHC7, or another convenient way how to prevent my programs taking all memory?

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