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  • Math/numerical formula every computer programmer should know

    - by aaa
    This is a follow-up question to What should every programmer know and Is mathematics necessary. So the question is, as a computer programmer, what is the most important/useful mathematical or numerical formula that you use? By Formula I mean anything that involves less obvious manipulations, whenever binomial coefficients or bit hacks. I work with multidimensional arrays and various matrix representations. So for me most commonly used formulas are: A(i,j,k,..) = a[i + j*Dim0 + k*Dim0*Dim1 + ... to map indexes to one dimension ( which is basic address calculation which many people do not seem to know). And triangular number T(i) = (i*i + i)/2 which is related to binomial coefficients, used to calculate address in triangular matrixes and many other things. What is your workhorse formula that you think programmer should know?

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  • Should I invest time in learning about OR\M or LINQ?

    - by Peter Smith
    I'm a .NET web developer primarily who occasionally writes console applications to mine data, cleanup tasks, etc. Most of what I do winds up involving a database which I currently design via sql server management studio, using stored procedures, and query analyzer. I also create a lot of web services which are consumed via AJAX applications. Do these technologies really help you in speeding up development times? Do you still have to build the database or object code first?

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  • Object serialization practical uses?

    - by nash
    How many software projects have you worked on used object serialization? I personally never came across a scenario where object serialization was used. One use case i can think of is, a server software storing objects to disk to save memory. Are there other types of software where object serialization is essential or preferred over a database?

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  • How to acces File over the Network

    - by Polo
    Hi! I am having a hard time on this one, I have à folder over the network wit public accès (no credential restriction). I am trying to do à File.Exist or Directory.Exist and I keep on having a exception. Can somewone tell me the good way to do IO over the network. EDIT 1 FOR DETAILS: if i do execture = \agoodip\Public\test.txt I get the file etc etc In my code it look like a basic Directory.Exist(@"\agoodip\Public") or File.exist(@"\agoodip\Public\test.txt") The exception I get is Path not found. Thanks!

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  • How do you pronounce "Enum"?

    - by Davy8
    In the spirit of this question how do you pronounce Enum? Tagging as subjective and community wiki obviously. I've heard E-Nuhm and E-Nnoom any others? Edit: Looks like we have a winner. Thought it'd be a closer race since most of the people at my work use the 2nd one.

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  • Reverse rendering of Urdu fonts

    - by Syed Muhammad Umair
    I am working on a project that is based on Urdu language in Ubuntu platform. I'm using Python language and have almost achieved my task. The problem is that, the Urdu text is rendered in reverse order. For example, consider the word ??? (which means work) consisting of the three letters: ? , ? , and ? The output is rendered in reverse order as ??? consisting of the three letters: ?, ?, and ? When copying this text to Open Office or opening the generated XML file in Firefox, the generated result is absolutely desired. I Am using Python 2.6 IDLE, its working perfect with Windows platform, which clearly shows its not the problem of IDLE. Am working on TKINTER GUI library. How can this problem be solved?

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  • How to sort a list in Scala by two fields?

    - by Twistleton
    how to sort a list in Scala by two fields, in this example I will sort by lastName and firstName? case class Row(var firstName: String, var lastName: String, var city: String) var rows = List(new Row("Oscar", "Wilde", "London"), new Row("Otto", "Swift", "Berlin"), new Row("Carl", "Swift", "Paris"), new Row("Hans", "Swift", "Dublin"), new Row("Hugo", "Swift", "Sligo")) rows.sortBy(_.lastName) I try things like this rows.sortBy(_.lastName + _.firstName) but it doesn't work. So I be curious for a good and easy solution. Thanks in advance! Pongo

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  • IP address problem

    - by mavric
    I built a TicTacToe game application (I'm using TCP protocol) that consist of server and client (that run two times to represent the 2 opponents). I have a problem and I can't find the solution for it, that is why I'm asking this question. the problem is : when the client try to connect the server on my machine, it never connect because of the IP address(obtained from the support tab from the local area connection in my windows) of my machine isn't correct. I tried to obtain my IP address from websites that told you your IP but I doesn't work. I have a problem to determine my IP address that any machine can connect to me from anywhere. p.s. I'm using router to connect the internet. thanks.

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  • my realtime network receiving time differs a lot, anyone can help?

    - by sguox002
    I wrote a program using tcpip sockets to send commands to a device and receive the data from the device. The data size would be around 200kB to 600KB. The computer is directly connected to the device using a 100MB network. I found that the sending packets always arrive at the computer at 100MB/s speed (I have debugging information on the unit and I also verified this using some network monitoring software), but the receiving time differs a lot from 40ms to 250ms, even if the size is the same (I have a receiving buffer about 700K and the receiving window of 8092 bytes and changing the window size does not change anything). The phenomena differs also on different computers, but on the same computer the problem is very stable. For example, receiving 300k bytes on computer a would be 40ms, but it may cost 200ms on another computer. I have disabled firewall, antivirus, all other network protocol except the TCP/IP. Any experts on this can give me some hints?

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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • Linux Kernel - Slab Allocator Question

    - by Drex
    I am playing around with the kernel and am looking at the kmem_cache files_cachep belonging to fork.c. It detects the sizeof(files_struct). My question is this: I have altered files_struct and added a rb_root (red/black tree root) using the built-in functionality in linux/rbtree.h. I can properly insert values into this tree. However, at some point, a segfault occurs and GDB backtraces the following information: (gdb) backtrace 0 0x08066ad7 in page_ok (page=) at arch/um/os-Linux/sys-i386/task_size.c:31 1 0x08066bdf in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100 2 0x0804a216 in linux_main (argc=1, argv=0xbfb05f14) at arch/um/kernel/um_arch.c:277 3 0x0804acdc in main (argc=1, argv=0xbfb05f14, envp=0xbfb05f1c) at arch/um/os-Linux/main.c:150 I have spent many hours trying to figure out why there is a segfault given that the red/black tree inserts properly. I'm thinking it's a memory allocation issue with new processes made by fork() of a parent process. Could this be the case and could it have something to do with kmem_cache files_cachep?

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  • Does MATLAB perform tail call optimization?

    - by Shea Levy
    I've recently learned Haskell, and am trying to carry the pure functional style over to my other code when possible. An important aspect of this is treating all variables as immutable, i.e. constants. In order to do so, many computations that would be implemented using loops in an imperative style have to be performed using recursion, which typically incurs a memory penalty due to the allocation a new stack frame for each function call. In the special case of a tail call (where the return value of a called function is immediately returned to the callee's caller), however, this penalty can be bypassed by a process called tail call optimization (in one method, this can be done by essentially replacing a call with a jmp after setting up the stack properly). Does MATLAB perform TCO by default, or is there a way to tell it to?

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  • How do I setup a Python development environment on Linux ?

    - by Rob Sobers
    I'm a .NET developer who knows very little about Python, but want to give it a test drive for a small project I'm working on. What tools and packages should I install on my machine? I'm looking for a common, somewhat comprehensive, development environment. I'll likely run Ubuntu 9.10, but I'm flexible. If Windows is a better option, that's fine too.

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  • Is selling a "website screen scraper" illegal?

    - by Yatendra Goel
    I have coded a "website screen scraper" and want to sell it commercially. I know that webpages scraped by the screen scraper are restricted to be scraped by the webmaser of that website. The robots.txt file of the website says that its webpages must not be scraped. So my question is whether selling that screen scraper is a crime or using that screen scraper is a crime in legal terms. I know that this question is related to law but I thought the software experts on SO must also have answer to this question.

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  • Best second language to learn for a native english speaking programmer?

    - by Tom Dignan
    I have always wanted to learn a foreign language, but I would like to pick one that can also help me the most in my career. I'm in the US, so it is not necessary for me to learn a second language to influence my career success, however I think knowing one and speaking it fluently could potentially put me in a more interesting career than if I did not. I would like to be able to travel the world, especially if I could have a reason to go one place or another. Which leads me to my question: What is the best second language to learn for a native English speaking programmer? (Especially from the US) Some ideas that come to mind for me are Mandarin, German, Japanese, French... I am looking for experienced opinions though! Thanks.

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  • Help me understand this C code

    - by Benjamin
    INT GetTree (HWND hWnd, HTREEITEM hItem, HKEY *pRoot, TCHAR *pszKey, INT nMax) { TV_ITEM tvi; TCHAR szName[256]; HTREEITEM hParent; HWND hwndTV = GetDlgItem (hWnd, ID_TREEV); memset (&tvi, 0, sizeof (tvi)); hParent = TreeView_GetParent (hwndTV, hItem); if (hParent) { // Get the parent of the parent of the... GetTree (hWnd, hParent, pRoot, pszKey, nMax); // Get the name of the item. tvi.mask = TVIF_TEXT; tvi.hItem = hItem; tvi.pszText = szName; tvi.cchTextMax = dim(szName); TreeView_GetItem (hwndTV, &tvi); //send the TVM_GETITEM message? lstrcat (pszKey, TEXT ("\\")); lstrcat (pszKey, szName); } else { *pszKey = TEXT ('\0'); szName[0] = TEXT ('\0'); // Get the name of the item. tvi.mask = TVIF_TEXT | TVIF_PARAM; tvi.hItem = hItem; tvi.pszText = szName; tvi.cchTextMax = dim(szName); if (TreeView_GetItem (hwndTV, &tvi)) //*pRoot = (HTREEITEM)tvi.lParam; //original hItem = (HTREEITEM)tvi.lParam; else { INT rc = GetLastError(); } } return 0; } The block of code that begins with the comment "Get the name of the item" does not make sense to me. If you are getting the listview item why does the code set the parameters of the item being retrieved? If you already had the values there would be no need to retrieve them. Secondly near the comment "original" is the original line of code which will compile with a warning under embedded visual c++ 4.0, but if you copy the exact same code into visual studio 2008 it will not compile. Since I did not write any of this code, and am trying to learn, is it possible the original author made a mistake on this line? The *pRoot should point to HKEY type yet he is casting to an HTREEITEM type which should never work since the data types don't match?

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  • How can I get the source code for ASTassistant?

    - by cyclotis04
    I'm trying to develop an application similar to ASTassistant, and in the article the author says that he included "the source code with the binaries." After downloading the ZIP folder, however, I've found no source. The program is written in REAL Basic, which I don't know anything about. Do I need to purchase REAL Basic to view ASTassistant's source code, or is it somewhere I haven't looked? Thanks

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  • How do I handle partial write completions from overlapped I/O using I/O Completion Ports

    - by Poni
    On Windows I/O completion ports, say I do this: void function() { WSASend("1111"); // A WSASend("2222"); // B WSASend("3333"); // C } If I got a "write-complete" that says 3 bytes of WSASend() A were sent, is it possible that right after that I'll get a "write-complete" that tells me that some or all of B & C were sent, or will TCP will hold them until I re-issue a WSASend() call with the rest of A's data? Or will TCP complete it automatically?

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  • Visual Studio 2010 Language Support

    - by inspectorG4dget
    Hello SO, I want to be able to develop code using Visual Studio 2010. I just got VS2010 and I'm not able to get the languages I want on it. The main reason that I'm asking this is that I'm trying to migrate to ONE IDE that does it all for me. Thus far eclipse has been doing a good job, but I've been informed that VS2010 is better and I'm trying to get into the groove of that standard So my question is two-fold. I am not able to find a complete list of languages supported by VS2010. What are these languages? How can I get VS2010 support for: a. Python/IronPython b. C/C++/C#/XNA c. Java My Googling has given me no promising/definitive results. I'd really appreciate any help.

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  • Please Help me add up the elements for this structure in Scheme/Lisp

    - by kunjaan
    I have an input which is of this form: (((lady-in-water . 1.25) (snake . 1.75) (run . 2.25) (just-my-luck . 1.5)) ((lady-in-water . 0.8235294117647058) (snake . 0.5882352941176471) (just-my-luck . 0.8235294117647058)) ((lady-in-water . 0.8888888888888888) (snake . 1.5555555555555554) (just-my-luck . 1.3333333333333333))) (context: the word denotes a movie and the number denotes the weighted rating submitted by the user) I need to add all the quantity and return a list which looks something like this ((lady-in-water 2.5) (snake 2.5) (run 2.25) (just-myluck 2.6)) How do I traverse the list and all the quantities? I am really stumped. Please help me. Thanks.

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  • What is your favourite cleverly written functional code?

    - by sdcvvc
    What are your favourite short, mind-blowing snippets in functional languages? My two favourite ones are (Haskell): powerset = filterM (const [True, False]) foldl f v xs = foldr (\x g a -> g (f a x)) id xs v -- from Hutton's tutorial (I tagged the question as Haskell, but examples in all languages - including non-FP ones - are welcome as long as they are in functional spirit.)

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