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• Simple reduction (NP completeness)

  - by Allen

  hey guys I'm looking for a means to prove that the bicriteria shortest path problem is np complete. That is, given a graph with lengths and weights, I need to know if a there exists a path in the graph from s to t with total length <= L and weight <= W. I know that i must take an NP complete problem and reduce it to this one. We have at our disposal the following problems to choose from: 3-SAT, independent set, vertex cover, hamiltonian cycle, and 3-dimensional matching. Any ideas on which may be viable? thanks

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• size of view not changing after frame change

  - by MikeNelson

  I have managed to do pretty complex things on iPhone but I am always stuck with views, frames, bounds, and simple stuff that defies any logic and don't work as expected. I have a self.view in my code and it has a lot of subviews on it. At some point of the code, I need to reduce the frame vertically to a specific size and later put it back as before. Then I have this code: [UIView beginAnimations:nil context:NULL]; [UIView setAnimationDuration:1.5]; // frame is changing to a newHeight (other parameters are the same as before) self.view.frame = CGRectMake (0, 0, originalWidth, newHeight); [UIView commitAnimations]; The result is simply, nothing. The view continues as before. The same size, the same position. No change. Why this kind of thing happens? how to solve that?

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• Memory in Eclipse

  - by user247866

  I'm getting the java.lang.OutOfMemoryError exception in Eclipse. I know that Eclipse by default uses heap size of 256M. I'm trying to increase it but nothing happens. For example: eclipse -vmargs -Xmx16g -XX:PermSize=2g -XX:MaxPermSize=2g I also tried different settings, using only the -Xmx option, using different cases of g, G, m, M, different memory sizes, but nothing helps. Does not matter which params I specify, the heap exception is thrown at the same time, so I assume there's something I'm doing wrong that Eclipse ignores the -Xmx parameter. I'm using a 32GB RAM machine and trying to execute something very simple such as: double[][] a = new double[15000][15000]; It only works when I reduce the array size to something around 10000 on 10000. I'm working on Linux and using the top command I can see how much memory the Java process is consuming; it's less than 2%. Thanks!

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• How to continuously fade a BitmapData to a certain color?

  - by Cay

  I'm drawing stuff on a bitmapData and I need to continuously fade every pixel to 0x808080 while still drawing (its for a DisplacementMapFilter)... I think this illustrates my problem: http://www.ventdaval.com/lab/grey.swf The simpler approach I tried was drawing a semi-transparent grey box on it, but it never reaches a single color (i.e. 0x808081 will never be turned to 0x808080)... The same kind of thing happens with a ColorMatrixFilter trying to progressively reduce the saturation and/or contrast. (the example above is applying a filter with -10 contrast every frame). I'm trying paletteMap now, and I'm sensing this could be the way to go, but I haven't been able to get it... any ideas?

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• dilemma about mysql. using condition to limit load on a dbf

  - by ondrobaco

  hi, I have a table of about 800 000 records. Its basically a log which I query often. I gave condition to query only queries that were entered last month in attempt to reduce the load on a database. My thinking is a) if the database goes only through the first month and then returns entries, its good. b) if the database goes through the whole database + checking the condition against every single record, it's actually worse than no condition. What is your opinion? How would you go about reducing load on a dbf?

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• Most useful parallel programming algorithm?

  - by Zubair

  I recenty asked a question about parallel programming algorithms which was closed quite fast due to my bad ability to communicate my intent: http://stackoverflow.com/questions/2407631/what-is-the-most-useful-parallel-programming-algorithm-closed I had also recently asked another question, specifically: http://stackoverflow.com/questions/2407493/is-mapreduce-such-a-generalisation-of-another-programming-principle/2407570#2407570 The other question was specifically about map reduce and to see if mapreduce was a more specific version of some other concept in parallel programming. This question (about a useful parallel programming algorithm) is more about the whole series of algorithms for parallel programming. You will have to excuse me though as I am quite new to parallel programming, so maybe MapReduce or something that is a more general form of mapreduce is the "only" parallel programming construct which is available, in which case I apologise for my ignorance

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• Is testability alone justification for dependency injection?

  - by fearofawhackplanet

  The advantages of DI, as far as I am aware, are: Reduced Dependencies More Reusable Code More Testable Code More Readable Code Say I have a repository, OrderRepository, which acts as a repository for an Order object generated through a Linq to Sql dbml. I can't make my orders repository generic as it performs mapping between the Linq Order entity and my own Order POCO domain class. Since the OrderRepository by necessity is dependent on a specific Linq to Sql DataContext, parameter passing of the DataContext can't really be said to make the code reuseable or reduce dependencies in any meaningful way. It also makes the code harder to read, as to instantiate the repository I now need to write new OrdersRepository(new MyLinqDataContext()) which additionally is contrary to the main purpose of the repository, that being to abstract/hide the existence of the DataContext from consuming code. So in general I think this would be a pretty horrible design, but it would give the benefit of facilitating unit testing. Is this enough justification? Or is there a third way? I'd be very interested in hearing opinions.

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• Using Dijkstra's algorithm with negative edges?

  - by Riddler

  Most books explain the reason the algorithm doesn't work with negative edges as nodes are deleted from the priority queue after the node is arrived at since the algorithm assumes the shortest distance has been found. However since negative edges can reduce the distance, a future shorter distance might be found; but since the node is deleted it cannot be updated. Wouldn't an obvious solution to this be to not delete the node? Why not keep the node in the queue, so if a future shorter distance is found, it can be updated? If I am misunderstanding the problem, what is preventing the algorithm from being used with negative edges?

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• What is the most efficient way to solve system of equations containing the digamma function?

  - by Neil G

  What is the most efficient way to solve system of equations involving the digamma function? I have a vector v and I want to solve for a vector w such that for all i: digamma(sum(w)) - digamma(w_i) = v_i and w_i 0 I found the gsl function gsl_sf_psi, which is the digamma function (calculated using some kind of series.) Is there an identity I can use to reduce the equations? Is my best bet to use a solver? I am using C++0x; which solver is easiest to use and fast?

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• How to shrink-to-fit an std::vector in a memory-efficient way?

  - by dehmann

  I would like to 'shrink-to-fit' an std::vector, to reduce its capacity to its exact size, so that additional memory is freed. The standard trick seems to be the one described here: template< typename T, class Allocator > void shrink_capacity(std::vector<T,Allocator>& v) { std::vector<T,Allocator>(v.begin(),v.end()).swap(v); } The whole point of shrink-to-fit is to save memory, but doesn't this method first create a deep copy and then swaps the instances? So at some point -- when the copy is constructed -- the memory usage is doubled? If that is the case, is there a more memory-friendly method of shrink-to-fit? (In my case the vector is really big and I cannot afford to have both the original plus a copy of it in memory at any time.)

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• Looking for actively maintained matrix math library for php

  - by Mnebuerquo

  Does anyone know where I might find a PHP matrix math library which is still actively maintained? I need to be able to do the basic matrix operations like reduce, transpose (including non-square matrices), invert, determinant, etc. This question was asked in the past, then closed with no answers. Now I need an answer to the same question. See these links to related questions: http://stackoverflow.com/questions/428473/matrix-artihmetic-in-php http://stackoverflow.com/questions/435074/matrix-arithmetic-in-php-again I was in the process of installing the pear Math_Matrix library when I saw these and realized it wouldn't help me. (Thanks Ben for putting that comment about transpose in your question.) I can code this stuff myself, but I would make me happier to see that there is a library for this somewhere.

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• Using PIG with Hadoop, how do I regex match parts of text with an unknown number of groups?

  - by lmonson

  I'm using Amazon's elastic map reduce. I have log files that look something like this random text foo="1" more random text foo="2" more text noise foo="1" blah blah blah foo="1" blah blah foo="3" blah blah foo="4" ... How can I write a pig expression to pick out all the numbers in the 'foo' expressions? I prefer tuples that look something like this: (1,2) (1) (1,3,4) I've tried the following: TUPLES = foreach LINES generate FLATTEN(EXTRACT(line,'foo="([0-9]+)"')); But this yields only the first match in each line: (1) (1) (1)

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• Best practices for using memcached in Rails?

  - by Matt

  Hello everybody, as database transcations in our app are getting more and more time consuming, we have started to use memcached to reduce the amount of queries passed to MySQL. All in all, it works fine and really saves a lot of time. But as caching was "silently appearing" as a workaround to give the app more juice, a lot of our models now contain code like this: def self.all_cached Rails.cache.fetch('object_name') { find( :all, :include => [associations]) } end This is getting more and more a pain as filling and flushing the cache happens in several classes accross the application. Now, I was wondering if there was a better way to abstract memcached logic to make it more powerful and easy to use across all needed models? I was thinking about having some kind of memcached-module which is included in all needed modules. But before playing around, I thought: Let's ask experts first :-) Thanks Matt

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• Stop Images from loading in UIWebView

  - by Zac Altman

  I have a website that I wish to load in a UIWebView, but it is full of images and takes ages to load. The images are useless, and only serve to reduce the usability on the iPhone. I dont own the website so I cannot change the site's actual code. The webpage is heavily linked in to the web with ASP.NET and AJAX (needs external files), so i dont think it is possible to have it load an HTML string. I want to stop the images from loading altogether. So how do i block them? Change the HTML code as its loading somehow, or block images from being loaded?

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• Consolidate the same image used multiple times in a PDF.

  - by Jack

  I am generating PDF documents using DevExpress XtraReports. I am using the same image over and over (in rows of status lights). The PDF generated seems to duplicate the image definition for each image included. I would prefer if it included the image once and referenced it wherever it needed another copy - this would drastically reduce the size of my PDF docs. Is there any way to achieve this using DevExpress or even post processed via a third party application. Any help is appreciated.

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• Subscribing to MSMQ over the internet

  - by Nathan Palmer

  I haven't been able to find a clear answer to this problem. Is there a good way to subscribe to a MSMQ through the internet? Ideally I need security both in authentication and encryption for this connection. But I would like the subscriber to act just like any other client that would be subscribed on the local network. I believe I have a couple of options here Expose the MSMQ ports publicly Put the MSMQ behind some type of WCF service (not sure if that works for a subscriber) What other options do I have? We're sitting in a .NET environment and the main problem domain that is trying to be solved is to change the remote connections from a pulling system to an event based system to reduce the load on the main server.

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• How to convert an existing callback interface to use boost signals & slots

  - by the_mandrill

  I've currently got a class that can notify a number of other objects via callbacks: class Callback { virtual NodulesChanged() =0; virtual TurkiesTwisted() =0; }; class Notifier { std::vector<Callback*> m_Callbacks; void AddCallback(Callback* cb) {m_Callbacks.push(cb); } ... void ChangeNodules() { for (iterator it=m_Callbacks.begin(); it!=m_Callbacks.end(); it++) { (*it)->NodulesChanged(); } } }; I'm considering changing this to use boost's signals and slots as it would be beneficial to reduce the likelihood of dangling pointers when the callee gets deleted, among other things. However, as it stands boost's signals seems more oriented towards dealing with function objects. What would be the best way of adapting my code to still use the callback interface but use signals and slots to deal with the connection and notification aspects?

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• Google App Engine - low-level datastore API flag?

  - by Keyur

  In my GAE-Java app, I'm using the low-level datastore API. Hence I don't need the GAE app instance to load any of the higher level data access libraries such as JPA, JDO, Data Nucleus, etc. Is there a flag that I can set to indicate that I don't want these libraries to be loaded? My motivation to do this is to reduce app instance startup time everywhere I can. Now I don't know if these libraries are loaded only on-demand or always. The dev environment logs messages related to data nucleus which seems to indicate that some of these libraries may be pre-loaded? I hope I'm wrong here. Thanks, Keyur

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• safely encode and pass a string from a html link to PHP program

  - by bert

  What series of steps would be reqired to safely encode and pass a string from a html href using javascript to construct the link to a php program. in javascript set up URL // encodes a URI component. path = "mypgm.php?from=" + encodeURIComponent(myvar) ; in php: // get passed variables $myvar = isset($_GET['myvar']) ? ($_GET['myvar']) : ''; // decode - (make the string readable) $myvar = (rawurldecode($myvar)); // converts characters to HTML entities (reduce risk of attack) $myvar = htmlentities($myvar); // maybe custom sanitize program as well? // see [http://stackoverflow.com/questions/2668854/php-sanitizing-strings-to-make-them-url-and-filename-safe][1] $myvar = sanitize($myvar);

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• Using xsl:key to store result of boolean expression

  - by hielsnoppe

  In my transformation there is an expression some elements are repeatedly tested against. To reduce redundancy I'd like to encapsulate this in an xsl:key like this (not working): <xsl:key name="td-is-empty" match="td" use="not(./node()[normalize-space(.) or ./node()])" /> The expected behaviour is the key to yield a boolean value of true in case the expression is evaluated successfully and otherwise false. Then I'd like to use it as follows: <xsl:template match="td[not(key('td-is-empty', .))]" /> Is this possible and in case yes, how?

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• Split or save a subset of a ESRI Shape SHP file to a new file?

  - by Eric Palakovich Carr

  I'm working with shape files in GeoDjango. Right now I'm trying to write a test for code that loads in a shape file and saves it to a database. The shape file currently has a feature count of 64,118. I'd like to reduce this to a handful so the test can quickly load it and confirm everything is right. Since shape files aren't in a text format, is there a free application or library I can use to pluck out a handful of features and save them to a new file? I should mention I don't have a license nor access to any of the ESRI product line.

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• ASP.NET MVC: What's the difference in concept between Service and Repository

  - by Richard77

  Hello, The question I'm asking is kind of subjective. I've seen twice, while exercising with real projects such as StoreFront, both Repository and Services. Sometimes they can just be folders or projects attached to the solution. But they contain classes and interfaces. So, I'd like to know what goes to the repository and what goes to the services. So far, I was familiar with repositories (we put methods and properties in the repository to reduce the complexity in the controller). How about the services? So, ASP.NET MVC: What's the difference in concept between Service and Repository? (Maybe none) My question is Kind of subjective, but I'd like to make sure that I'm not missing anything. Thanks for helping

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• Is JBehave a good choice for Web Service Automated Testing?

  - by Vanchinathan

  Hi All, We have a requirement at my workplace to automate the webservice testing. We have been using QTP scripts to do so. We as a team, Kind of leaning towards Jbehave as a choice. Is JBehave a good choice for web service functional testing automation? We do use Soap UI to test manually. But we are planning to automate the functional and regression testing to reduce the release cycle time. Suggestions welcome.

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• Avoiding problem of overwriting files which are in use

  - by zaf

  For example on a high traffic web server. To reduce problems when switching a file I usually rename the old file out and then rename in the new file. I was told some time ago that renaming a file does not change the 'inode data' so that processes reading the file can keep doing so without glitches. And, of course, rather than copying in the new file it is faster and safer to rename a temp copy. Is this still best practice and if not what do you do?

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• Accelerometer Values from Android/iPhone device

  - by mrlinx

  I'm trying to map my movements with a android device into an OpenGL scene. I've recorded accelerometer values for a simples movement: Moving the phone (lies flat on a table) 10cm forward (+x), and then 10cm backward (-x). The problem is that this values when used to calculate velocity and position, makes only the opengl cube go forward. Seems like the negative acceleration recorded was not enough to reduce the speed and invert its movement. What can be the problem? This is my function that updates the velocity and position every time new data comes in: void updatePosition(double T2) { double T = 0.005; Vec3 old_pos = position.clone(), old_vel = velocity.clone(); velocity = old_vel.plus(acceleration.times(T)); position = old_pos.plus(old_vel.times(T).plus(acceleration.times(0.5 * Math.pow(T, 2)))); } This is the X,Y,Z accelerometer values over the entire captured time:

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