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• Machine Learning Algorithm for Parallel Nodes

  - by FreshCode

  I want to apply machine learning to a classification problem in a parallel environment. Several independent nodes, each with multiple on/off sensors, can communicate their sensor data with the goal of classifying an event defined by a heuristic, training data or both. Each peer will be measuring the same data from their unique perspective and will attempt to classify the result while taking into account that any neighbouring node (or its sensors or just the connection to the node) could be faulty. Nodes should function as equal peers and determine the most likely classification by communicating their results. Ultimately each node should make a decision based on their own sensor data and their peers' data. If it matters, false positives are OK (albeit undesirable) but false negatives are totally unacceptable. Given that each final classification will receive good or bad feedback, what would be an appropriate machine learning algorithm to approach this problem with if the nodes could communicate with each other to determine the most likely classification?

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• Cocoa - How to copy files to /usr/share?

  - by cyaconi

  Hi all. I'm developing an "installation" like cocoa application wich needs to take care of some http request, some file system reading, copying files to /usr/share, set up cron (not launchd) and ask some information to user. I discarded PackageMaker since I need more flexibility. Currently everything is going well, but on my last installation step, I need to: Delete my previously installed application folder (if exists). It's always the same path: /usr/share/MY_APP Create again the application folder at: /usr/share/MY_APP Copy application files to /usr/share/MY_APP Update a cron job It's very important that /usr/share/MY_APP keeps protected with administrative privileges, so a regular shouldn't delete it. What would be the best approach to implement those steps? BTW, I'm using Xcode 3.2. Thanks a lot! Carlos.

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• Get last n lines of a file with Python, similar to tail

  - by Armin Ronacher

  I'm writing a log file viewer for a web application and for that I want to paginate through the lines of the log file. The items in the file are line based with the newest item on the bottom. So I need a tail() method that can read n lines from the bottom and supports an offset. What I came up with looks like this: def tail(f, n, offset=0): """Reads a n lines from f with an offset of offset lines.""" avg_line_length = 74 to_read = n + offset while 1: try: f.seek(-(avg_line_length * to_read), 2) except IOError: # woops. apparently file is smaller than what we want # to step back, go to the beginning instead f.seek(0) pos = f.tell() lines = f.read().splitlines() if len(lines) >= to_read or pos == 0: return lines[-to_read:offset and -offset or None] avg_line_length *= 1.3 Is this a reasonable approach? What is the recommended way to tail log files with offsets?

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• Best solution for a comment table for multiple content types

  - by KRTac

  I'm currently designing a comments table for a site I'm building. Users will be able to upload images, link videos and add audio files to the profile. Each of these types of content must be commentable. Now I'm wondering what's the best approach to this. My current options are: 1. to have one big comments table and a link tables for every content type (comments_videos, ...) with comment_id and _id. 2. to have comments separated by the type of content their for. So each type of content would have his own comments table with the comments for that type.

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• How do I synchronize access to shared memory in LynxOS/POSIX?

  - by GrahamS

  I am implementing two processes on a LynxOS SE (POSIX conformant) system that will communicate via shared memory. One process will act as a "producer" and the other a "consumer". In a multi-threaded system my approach to this would be to use a mutex and condvar (condition variable) pair, with the consumer waiting on the condvar (with pthread_cond_wait) and the producer signalling it (with pthread_cond_signal) when the shared memory is updated. How do I achieve this in a multi-process, rather than multi-threaded, architecture? Is there a LynxOS/POSIX way to create a condvar/mutex pair that can be used between processes? Or is some other synchronization mechanism more appropriate in this scenario?

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• Is it more efficient to always run a delete query, or to check if that information exists first

  - by Scarface

  Ok this is going to seem like a dumb question to experienced developers, but questions like this bother me until I ask them. So... is it more efficient to always run a delete query by default whether an entry exists or not, for example to delete a user name after a certain period of time (DELETE * from table where username=user), or should you check if that entry exists first using a select query and mysql_num_rows. What uses more processor on the server side? Obviously one approach contains more code, but I was wondering if certain mysql operations used a lot more cpu than others.

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• Overriding as_json has no effect?

  - by Ola Tuvesson

  I'm trying to override as_json in one of my models, partly to include data from another model, partly to strip out some unnecessary fields. From what I've read this is the preferred approach in Rails 3. To keep it simple, let's say I've got something like: class Country < ActiveRecord::Base def as_json(options={}) super( :only => [:id,:name] ) end end and in my controller simply def show respond_to do |format| format.json { render :json => @country } end end Yet whatever i try, the output always contains the full data, the fields are not filtered by the ":only" clause. Basically, my override doesn't seem to kick in, though if I change it to, say... class Country < ActiveRecord::Base def as_json(options={}) {foo: "bar"} end end ...I do indeed get the expected JSON output. Have I simply got the syntax wrong?

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• Django equivalent for latest entry for each user

  - by paul-ogrady

  Hi, I'm surprised this question hasn't come up. Couldn't find much on the web. Using Entry.objects.latest('created_at') I can recover the latest entry for all Entry objects, but say if I want the latest entry for each user? This is something similar to an SQL latest record query. But how do I achieve this using the ORM? Here is my approach I'm wondering if it is the most efficient way to do what I want. First I perform a sub query: Objects are grouped by user and the Max (latest) created_by field is returned for each user (created_at__max) I then filter Entry objects based on the results in the subquery and get the required objects. Entry.objects.filter(created_at__in=Entry.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) or using a manager: class UsersLatest(models.Manager): def get_query_set(self): return Super(UsersLatest,self).get_query_set().filter(created_at__in=self.model.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) Is there a more efficient way? possibly without sub query? Thanks, Paul

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• comparing two angles

  - by Elazar Leibovich

  Given four points in the plane, A,B,X,Y, I wish to determine which of the following two angles is smaller ?ABX or ?ABY. I'd rather not use cos or sqrt, in order to preserve accuracy. In the case where A=(-1,0),B=(0,0), I can compare the two angles ?ABX and ?ABY, by calculating the dot product of the vectors X,Y, and watch it's sign. What I can do in this case is: Determine whether or not ABX turns right or left If ABX turns left check whether or not Y and A are on the same side of the line on segment BX. If they are - ?ABX is a smaller than ABY. If ABX turns right, then Y and A on the same side of BX means that ?ABX is larger than ?ABY. But this seems too complicated to me. Any simpler approach?

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• Using "class/object" MooTools-style events in jQuery

  - by Infinity

  One of the nice things about MooTools, is that it lets you easily assign/fire events to objects, for example: var playerSingleton = new (new Class({ Implements: [Events], initialize: function() {}, setVolume: function() { // do some stuff.. this.fireEvent('volumeChanged') } })); // Somewhere else... playerSingleton.addEvent('volumeChanged', function() { // do something when volume changes }); playerSingleton.setVolume(75); // bam our event fires. How would something like this be done with jQuery? I know there's .bind and .trigger, but it seems like the only way to do this is to bind/fire events to the window object: $(window).bind('volumeChanged', fn); Is there anything better than this, more like the MooTools approach? Thanks!

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• OpenMP + SSE gives no speedup

  - by Sayan Ghosh

  Hi, My Professor found out this interesting experiment of 3D Linearly separable Kernel Convolution using SSE and OpenMP, and gave the task to me to benchmark the statistics on our system. The author claims a crazy 18 fold speedup from the serial approach! Might not be always, but we were expecting at least a 2-4 times speedup running this on a Dual Core Intel. http://software.intel.com/en-us/articles/16bit-3d-convolution-sse4openmp-implementation-on-penryn-cpu/#comment-41994 Alas, we could find exactly no speedup. The serial code performs always better, with or without OpenMP. I am using Linux, and observed a certain trend...when no other processes are running on the system, after a while the loadavg starts increasing, and the the %CPU utilization falls down. Another probable false positive which I ran into accidentally...I started the program, then immediately paused it. Then I ran it on background with bg, and saw a speedup of more than 2. This happens all the time! Any advice would be great. Thanks, Sayan

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• Tips on creating a "build a bracelet" app

  - by Felipe Caldas

  I have an idea for an app/game which is basically a build your own bracelet. I will give to the user, say, 5 different types of beads, and the user and drag those beads into a line that is previously drawn in the screen and create his/her bracelet. I am now thinking on the best way to approach this. Would be using the android's OpenGL libraries (and therefore, creating the beads and loading its textures) the best and easiest way? Ultimately, I would like to push new beads into the application whenever I have a new bead texture. Thanks, Felipe

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• managing library dependencies with Boost.Build and C++

  - by user931794

  I want to develop a project which can be built on a bunch of different platforms. The project code will be in C++, what's the the best way to manage libraries? I plan on using bjam as the build system because I'm going to be depending on Boost and their unit testing framework as well. The two dependent libraries are Boost itself and FLTK. The possibilities that come to mind for library management are: include build artifacts (binaries) and headers for all supported platforms in-tree include complete source for all dependent libraries in-tree, and somehow script them as dependencies A combination of 1 and 2, like node.js does with v8 inform the user that they need to build the libraries themselves and then have them on the PATH or in some special directory, like libcurl does with its dependencies What is the best approach here? The project will probably not grow beyond a few thousand lines over the next six months, but I want to make the right choice here so that I don't have to come back and switch everything around later.

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• Linq sql Attach, Update Check set to Never, but still Concurrency conflicts

  - by remdao

  In the dbml designer I've set Update Check to Never on all properties. But i still get an exception when doing Attach: "An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported." This approach seems to have worked for others on here, but there must be something I've missed. using(TheDataContext dc = new TheDataContext()) { test = dc.Members.FirstOrDefault(m => m.fltId == 1); } test.Name = "test2"; using(TheDataContext dc = new TheDataContext()) { dc.Members.Attach(test, true); dc.SubmitChanges(); }

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• How to include javascript/css once with Struts 1.x

  - by Felix

  If this is the wrong approach, please suggest something better, but my current efforts have been trying to find something that exists for a single page load, such that I can cache which javascript/css files have been included so as to only include them once. I thought in a TagSupport subclass I could use (HttpServletRequest)pageContext.getRequest().getParameterMap().put(srcKey,true) but the request is per jsp, not per page load so it was a failure. I could set up a filter in web.xml, but it seems I would have to search the response for duplicates and rewrite the response...pain. I could try to store things in the session, but there are headaches with clearing values... Any help would be appreciated.

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• How can I "best fit" an arbitrary cairo (pycairo) path?

  - by Daniel Straight

  It seems like given the information in stroke_extents() and the translate(x, y) and scale(x, y) functions, I should be able to take any arbitrary cairo (I'm using pycairo) path and "best fit" it. In other words, center it and expand it to fill the available space. Before drawing the path, I have scaled the canvas such that the origin is the lower left corner, up is y+, right is x+, and the height and width are both 1. Given these conditions, this code seems to correctly scale the path: # cr is the canvas extents = cr.stroke_extents() x_size = abs(extents[0]) + abs(extents[2]) y_size = abs(extents[1]) + abs(extents[3]) cr.scale(1.0 / x_size, 1.0 / y_size) I cannot for the life of me figure out the translating though. Is there a simpler approach? How can I "best fit" a cairo path on its canvas? Please ask for clarification if anything is unclear in this question.

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• Visual Studio's CSS Intellisense - Absolute paths & MasterPage files

  - by Overflew

  Hi there. I've noticed that to get CSS-Intellisense working in VS, the paths have to be relative - Is this the case? However, it seems <link href="/resources/test.css" [...] /> is far more practical than <link href="resources/test.css" [...] /> I'm including the CSS in the master page, and don't see much good in including it as a content block, just to get the relative paths correct for each directory depth. I've had a quick try with inline code resolving the path, but no dice there either (for Intellisense). I feel I'm missing something fairly simple - What's the correct approach here to have CSS Intellisense work across the pages in the app during dev, and render fine in any deployed state? Cheers. (Note - I'm aware that a <% if (false) { % type hack is required for user controls)

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• How to prevent column b containing the same value as any column a in Oracle?

  - by Janek Bogucki

  What is a good way to prevent a table with 2 columns, a and b, from having any record where column b is equal to any value in column a? This would be used for a table of corrections like this, MR -> Mr Prf. -> Prof. MRs -> Mrs I can see how it could be done with a trigger and a subquery assuming no concurrent activity but a more declarative approach would be preferable. This is an example of what should be prevented, Wing Commdr. -> Wing Cdr. Wing Cdr. -> Wing Commander Ideally the solution would work with concurrent inserts and updates.

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• What are the pros and cons of using an in memeory DB rather than a ThreadLocal

  - by Pangea

  we have been using ThreadLocal so far to carry some data so as to not clutter the API. However below are some of issues of using thread local that which I dont like 1) over the years the data items being carried in thread local has increased 2) Since we started using threads (for some light weight processing), we have also migrating these data to the threads in the pool and copying them back again I am thinking of using an in memory DB for these (we doesnt want to add this to the API). I wondering if this approach is good. What r the pros and cons. thx in advance.

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• NSKeyedArchiver save method ( that i made) crashed the iphone simulator

  - by Kevin

  i saw this approach on a tutorial, and the message is working for their example but when i implement this it does not work. from what i can tell the iphone simulator crashes when i do a [ self saveSettingsData]. TheSettings is class object that i declare and initialize in the appdelagate with these methods. the error says terminating due to uncaught exception. i am new to the iphone sdk and objective, so i really can't figure out what is going on thanks to any one who can help, i am ready to literally pull my hair out. (NSString *) SettingsDataFilePath { NSString * settingsDataFilePath ; NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) ; NSString * documentsDirectory = [paths objectAtIndex:0] ; settingsDataFilePath = [[documentsDirectory stringByAppendingPathComponent: @"SetggggtingsData.plist" ] retain] ; return settingsDataFilePath ; } (void) saveSettingsData { [NSKeyedArchiver archiveRootObject:[TheSettings copy] toFile:[self SettingsDataFilePath]] ;

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• How do I access variables with hyphenated names in Smarty?

  - by abeger

  I've got a PHP page that parses an XML file with SimpleXml, then passes that object to a Smarty template. My problem is that the XML file has hyphens in its tag names, e.g. video-player. In PHP, this is no problem, I just use $xml->{'video-player'} and everything's fine. Smarty, on the other hand, throws a fit when I try to use that syntax. The only solution I've come up with so far is to use a variable to store the name, e.g., { assign var=name value="video-player" } { $xml->$name } But this isn't terribly graceful to say the least. Is there another, better, approach to referring to a hyphenated variable name in Smarty?

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• scanf("%d", char*) - char-as-int format string?

  - by SF.

  What is the format string modifier for char-as-number? I want to read in a number never exceeding 255 (actually much less) into an unsigned char type variable using sscanf. Using the typical char source[] = "x32"; char separator; unsigned char dest; int len; len = sscanf(source,"%c%d",&separator,&dest); // validate and proceed... I'm getting the expected warning: argument 4 of sscanf is type char*, int* expected. As I understand the specs, there is no modifier for char (like %sd for short, or %lld for 64-bit long) is it dangerous? (will overflow just overflow (roll-over) the variable or will it write outside the allocated space?) is there a prettier way to achieve that than allocating a temporary int variable? ...or would you suggest an entirely different approach altogether?

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• Restart IIS7 webapp for debug in VS2008

  - by spender

  I'm developing an ASP.NET asyc generic handler which uses a static System.Threading.Timer instance to feed data to the response output stream while the context is in the asynchronous phase. I'm having issues at startup that I'd like to debug. Currently, because of the long-lived nature of the timer, I'm manually killing w3wp.exe in order to cause the application to restart. I'm aware that there are other ways to do this, but this is the best workflow I can find! Isn't there a way to force a cold start when I hit f5, instead of the standard VS approach of attaching to the existing IIS process?

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• How To Aggregate API Data?

  - by Mindblip

  Hi, I have a system that connects to 2 popular APIs. I need to aggregate the data from each into a unified result that can then be paginated. The scope of the project means that the system could end up supporting 10's of APIs. Each API imposes a max limit of 50 results per request. What is the best way of aggregating this data so that it is reliable i.e ordered, no duplicates etc I am using CakePHP framework on a LAMP environment, however, I think this question relates to all programming languages. My approach so far is to query the search API of each provider and then populate a MySQL table. From this the results are ordered, paginated etc. However, my concern is performance: API communication, parsing, inserting and then reading all in one execution. Am I missing something, does anyone have any other ideas? I'm sure this is a common problem with many alternative solutions. Any help would be greatly appreciated. Thanks, Paul

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• [Java] Form data transition into entity beans to persist them by the server side ORM

  - by cscsaba242

  Hello guys, Is there any good explanation or tutorial which describes the common way how can we create entity beans from the received data of the form ? The main reason of my question the treating the received ids (e.g id of country,city and so forth) which is the way from the id to entity ? Example: ................Client side form username:String countryid:Integer (could be a drop down) ................Server side entities public class UserBean { String username; CountryBean Country; } public class CountryBean { String cityname; Integer id; } ............................................ Maybe the question is dependent of the used technology, but I guess there is a very common way. I would like to comprehend the conventional approach of this problem. (For the sake of the completeness I would like to save the form data (received by Stripes) by JPA) Thanks advance. cscsaba242

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