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  • Thread management advice - Is TPL a good idea?

    - by Ian
    I'm hoping to get some advice on the use of thread managment and hopefully the task parallel library, because I'm not sure I've been going down the correct route. Probably best is that I give an outline of what I'm trying to do. Given a Problem I need to generate a Solution using a heuristic based algorithm. I start of by calculating a base solution, this operation I don't think can be parallelised so we don't need to worry about. Once the inital solution has been generated, I want to trigger n threads, which attempt to find a better solution. These threads need to do a couple of things: They need to be initalized with a different 'optimization metric'. In other words they are attempting to optimize different things, with a precedence level set within code. This means they all run slightly different calculation engines. I'm not sure if I can do this with the TPL.. If one of the threads finds a better solution that the currently best known solution (which needs to be shared across all threads) then it needs to update the best solution, and force a number of other threads to restart (again this depends on precedence levels of the optimization metrics). I may also wish to combine certain calculations across threads (e.g. keep a union of probabilities for a certain approach to the problem). This is probably more optional though. The whole system needs to be thread safe obviously and I want it to be running as fast as possible. I tried quite an implementation that involved managing my own threads and shutting them down etc, but it started getting quite complicated, and I'm now wondering if the TPL might be better. I'm wondering if anyone can offer any general guidance? Thanks...

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  • MongoDB: What's the point of using MapReduce without parallelism?

    - by netvope
    Quoting http://www.mongodb.org/display/DOCS/MapReduce#MapReduce-Parallelism As of right now, MapReduce jobs on a single mongod process are single threaded Without parallelism, what are the benefits of MapReduce compared to simpler or more traditional methods for queries and data aggregation? To avoid confusion: the question is NOT "what are the benefits of document-oriented DB over traditional relational DB"

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  • I/O Asynchronous Completion

    - by lockedscope
    In the following, it is said that an I/O handle must be associated with the thread pool but i could not find where in the given example an handle is associated with the thread. Which function or code helps to bind the file handle in that example? Using asynchronous I/O completion events, a thread from the thread pool processes data only when the data is received, and once the data has been processed, the thread returns to the thread pool. To make an asynchronous I/O call, an operating-system I/O handle must be associated with the thread pool and a callback method must be specified. When the I/O operation completes, a thread from the thread pool invokes the callback method. http://msdn.microsoft.com/en-us/library/aa720215(VS.71).aspx

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  • minimum enclosing rectangle of fixed aspect ratio

    - by Ramya Narasimha
    I have an Image with many rectangles at different positions in the image and of different sizes (both overlapping and non-overlapping). I also have a non-negative scores associated with each of these rectangles. My problem now is to find one larger rectangle *of a fixed (given) aspect ratio* that encloses as many of these rectangles as possible. I am looking for an algorithm to do this, if anyone has a solution, even a partial one it would be helpful. Please note that the positions of the rectangles in the image is fixed and cannot be moved around and there is no orientation issue as all of them are upright.

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  • C++ converting binary(P5) image to ascii(P2) image (.pgm)

    - by tubby
    I am writing a simple program to convert grayscale binary (P5) to grayscale ascii (P2) but am having trouble reading in the binary and converting it to int. #include <iostream> #include <fstream> #include <sstream> using namespace::std; int usage(char* arg) { // exit program cout << arg << ": Error" << endl; return -1; } int main(int argc, char* argv[]) { int rows, cols, size, greylevels; string filetype; // open stream in binary mode ifstream istr(argv[1], ios::in | ios::binary); if(istr.fail()) return usage(argv[1]); // parse header istr >> filetype >> rows >> cols >> greylevels; size = rows * cols; // check data cout << "filetype: " << filetype << endl; cout << "rows: " << rows << endl; cout << "cols: " << cols << endl; cout << "greylevels: " << greylevels << endl; cout << "size: " << size << endl; // parse data values int* data = new int[size]; int fail_tracker = 0; // find which pixel failing on for(int* ptr = data; ptr < data+size; ptr++) { char t_ch; // read in binary char istr.read(&t_ch, sizeof(char)); // convert to integer int t_data = static_cast<int>(t_ch); // check if legal pixel if(t_data < 0 || t_data > greylevels) { cout << "Failed on pixel: " << fail_tracker << endl; cout << "Pixel value: " << t_data << endl; return usage(argv[1]); } // if passes add value to data array *ptr = t_data; fail_tracker++; } // close the stream istr.close(); // write a new P2 binary ascii image ofstream ostr("greyscale_ascii_version.pgm"); // write header ostr << "P2 " << rows << cols << greylevels << endl; // write data int line_ctr = 0; for(int* ptr = data; ptr < data+size; ptr++) { // print pixel value ostr << *ptr << " "; // endl every ~20 pixels for some readability if(++line_ctr % 20 == 0) ostr << endl; } ostr.close(); // clean up delete [] data; return 0; } sample image - Pulled this from an old post. Removed the comment within the image file as I am not worried about this functionality now. When compiled with g++ I get output: $> ./a.out a.pgm filetype: P5 rows: 1024 cols: 768 greylevels: 255 size: 786432 Failed on pixel: 1 Pixel value: -110 a.pgm: Error The image is a little duck and there's no way the pixel value can be -110...where am I going wrong? Thanks.

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  • Working with images in Scala

    - by dbyrne
    I am generating large PNG files from a Scala program. Currently, I am doing it the same way I would do it in java. I am creating a new BufferedImage and setting each pixel to the correct color. This works fine, but I am wondering if there are any good libraries for working with images in Scala? I am looking for something like Ruby's RMagick library.

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  • What hash algorithms are paralellizable? Optimizing the hashing of large files utilizing on mult-co

    - by DanO
    I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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  • Replacing all GUIDs in a file with new GUIDs from the command line

    - by Josh Petrie
    I have a file containing a large number of occurrences of the string Guid="GUID HERE" (where GUID HERE is a unique GUID at each occurrence) and I want to replace every existing GUID with a new unique GUID. This is on a Windows development machine, so I can generate unique GUIDs with uuidgen.exe (which produces a GUID on stdout every time it is run). I have sed and such available (but no awk oddly enough). I am basically trying to figure out if it is possible (and if so, how) to use the output of a command-line program as the replacement text in a sed substitution expression so that I can make this replacement with a minimum of effort on my part. I don't need to use sed -- if there's another way to do it, such as some crazy vim-fu or some other program, that would work as well -- but I'd prefer solutions that utilize a minimal set of *nix programs since I'm not really on *nix machines. To be clear, if I have a file like this: etc etc Guid="A" etc etc Guid="B" I would like it to become this: etc etc Guid="C" etc etc Guid="D" where A, B, C, D are actual GUIDs, of course. (for example, I have seen xargs used for things similar to this, but it's not available on the machines I need this to run on, either. I could install it if it's really the only way, although I'd rather not)

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  • "A generic error occurred in GDI+" error while showing uploaded images

    - by Prasad
    i am using the following code to show the image that has been saved in my database from my asp.net mvc(C#) application:. public ActionResult GetSiteHeaderLogo() { SiteHeader _siteHeader = new SiteHeader(); Image imgImage = null; long userId = Utility.GetUserIdFromSession(); if (userId > 0) { _siteHeader = this.siteBLL.GetSiteHeaderLogo(userId); if (_siteHeader.Logo != null && _siteHeader.Logo.Length > 0) { byte[] _imageBytes = _siteHeader.Logo; if (_imageBytes != null) { using (System.IO.MemoryStream imageStream = new System.IO.MemoryStream(_imageBytes)) { imgImage = Image.FromStream(imageStream); } } string sFileExtension = _siteHeader.FileName.Substring(_siteHeader.FileName.IndexOf('.') + 1, _siteHeader.FileName.Length - (_siteHeader.FileName.IndexOf('.') + 1)); Response.ContentType = Utility.GetContentTypeByExtension(sFileExtension.ToLower()); Response.Cache.SetCacheability(HttpCacheability.NoCache); Response.BufferOutput = false; if (imgImage != null) { ImageFormat _imageFormat = Utility.GetImageFormat(sFileExtension.ToLower()); imgImage.Save(Response.OutputStream, _imageFormat); imgImage.Dispose(); } } } return new EmptyResult(); } It works fine when i upload original image. But when i upload any downloaded images, it throws the following error: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderParameters encoderParams) at System.Drawing.Image.Save(Stream stream, ImageFormat format) For. Ex: When i upload the original image, it shows as logo in my site and i downloaded that logo from the site and when i re-upload the same downloaded image, it throws the above error. It seems very weird to me and not able to find why its happening. Any ideas on this?

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  • how many processors can I get in a block on cuda GPU?

    - by Vickey
    hi all, I have two questions to ask 1) If I create only one block of threads in cuda and execute the my parallel program on it then is it possible that more than one processors would be given to single block so that my program get some benefit of multiprocessor platform ? 2) can I synchronize the threads of different blocks ? if yes please give some hints. Thanks in advance since I know I'll get replies as always I get.

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  • .NET: How to ignore comments when reading a XML file into a XmlDocument?

    - by tunnuz
    Hello, I am trying to read a XML document with C#, I am doing it this way: XmlDocument myData = new XmlDocument(); myData.Load("datafile.xml"); anyway, I sometimes get comments when reading XmlNode.ChildNodes. Is there a way to avoid that? I know that you can avoid reading comments if you use XmlReader, but then, how to get the XmlDocument out of a XmlReader? Thank you Tommaso

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  • Edit axes to an image in matlab ?

    - by ZaZu
    Hello, I would like to edit the axes in my series of images being displayed .. This is how my image looks like : As you can see, it starts from 0 to ~~500 from top to bottom, can I invert that ? Plus I want to mirror the image being shown, so that it starts from left to right ... Or if its possible, let the axes show from right to left ? Thanks !

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  • Understanding The Convolution Matrix

    - by Ryan Naddy
    I am learning about the Convolution Matrix, and I understand how they work, but I don't understand how to know before hand what the output of a Matrix will look like. For example lets say I want to add a blur to an image, I could guess 10,000+ different combinations of numbers before I get the correct one. I do know though that this formula will give me a blur effect, but I have no idea why. float[] sharpen = new float[] { 1/9f, 1/9f, 1/9f, 1/9f, 1/9f, 1/9f, 1/9f, 1/9f, 1/9f }; Can anyone either explain to me how this works or point me to some article, that explains this? I would like to know before hand what a possible output of the matrix will be without guessing. Basically I would like to know why do we put that number in the filed, and why not some other number?

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  • How to printf a time_t variable as a floating point number?

    - by soneangel
    Hi guys, I'm using a time_t variable in C (openMP enviroment) to keep cpu execution time...I define a float value sum_tot_time to sum time for all cpu's...I mean sum_tot_time is the sum of cpu's time_t values. The problem is that printing the value sum_tot_time it appear as an integer or long, by the way without its decimal part! I tried in these ways: to printf sum_tot_time as a double being a double value to printf sum_tot_time as float being a float value to printf sum_tot_time as double being a time_t value to printf sum_tot_time as float being a time_t value Please help me!!

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  • What is a good way of Enhancing contrast of color images?

    - by erjik
    I split color image for 3 channels and made a contrast enhancement of each channel. Then merged them together, I like the image at the result, but it has different colors. Black objects became yellow and so on... EDIT: The algorithm I used is to calculate the 5th percentile and the 95th percentile as min and max values, and then expand the values of image so that it will have min and max values as 0 and 255. If there is a better approach please tell me.

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  • Finding many local max in an image (using MatLab)

    - by wenh42
    How do you go about figuring our multiple max in a 2D image where the max aren't necessarily all the same height? I have found that the imregionalmax(), imextendedmax(), and findpeaks() functions aren't necessarily that helpful because they give many local max that are really just maxes within the background noise. I tried bw=arrayimdilate(array,[1 1 1; 1 0 1; 1 1 1]) but that also is kind of limited for the same reasons (same thing with expanding the matrix that it uses). I'd definitely appreciate some help..

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  • Embarrassingly parallel workflow creates too many output files

    - by Hooked
    On a Linux cluster I run many (N > 10^6) independent computations. Each computation takes only a few minutes and the output is a handful of lines. When N was small I was able to store each result in a separate file to be parsed later. With large N however, I find that I am wasting storage space (for the file creation) and simple commands like ls require extra care due to internal limits of bash: -bash: /bin/ls: Argument list too long. Each computation is required to run through a qsub scheduling algorithm so I am unable to create a master program which simply aggregates the output data to a single file. The simple solution of appending to a single fails when two programs finish at the same time and interleave their output. I have no admin access to the cluster, so installing a system-wide database is not an option. How can I collate the output data from embarrassingly parallel computation before it gets unmanageable?

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  • Can I process video using flash?

    - by Roman
    I want to have a web page where user can activate his/her web-camera and send video to another user. Additionally to that I want to have a possibility to process video on the client side. In more details, I want to have a program which analyze video on the client side. Is it possible to do it with Flash?

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  • How to make disconnected closed curves connected by adding a shortest path using MATLAB?

    - by user198729
    bwlabel can be used to get disconnected objects in an image: [L Ne] = bwlabel(image); I want to make the objects(But my target is only the contours(closed curve) of these objects) connected by adding a shortest path where necessary. How do I approach this? UPDATE Or how to dilate the closed curves so that they get connected? How to calculate the shortest path between two disconnected closed curves?

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  • CUDA small kernel 2d convolution - how to do it

    - by paulAl
    I've been experimenting with CUDA kernels for days to perform a fast 2D convolution between a 500x500 image (but I could also vary the dimensions) and a very small 2D kernel (a laplacian 2d kernel, so it's a 3x3 kernel.. too small to take a huge advantage with all the cuda threads). I created a CPU classic implementation (two for loops, as easy as you would think) and then I started creating CUDA kernels. After a few disappointing attempts to perform a faster convolution I ended up with this code: http://www.evl.uic.edu/sjames/cs525/final.html (see the Shared Memory section), it basically lets a 16x16 threads block load all the convolution data he needs in the shared memory and then performs the convolution. Nothing, the CPU is still a lot faster. I didn't try the FFT approach because the CUDA SDK states that it is efficient with large kernel sizes. Whether or not you read everything I wrote, my question is: how can I perform a fast 2D convolution between a relatively large image and a very small kernel (3x3) with CUDA?

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  • sum of logarithams of prime numbers

    - by nadi
    Write a program that computes the sum of the logarithms of all the primes from 2 to some number n, and print out the sum of the logs of the primes, the number n, and the ratio of these two quantities. Test this for different values of n.

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