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• what is the idea behind scaling an image using lanczos?

  - by banister

  Hi, I'm interested in image scaling algorithms and have implemented the bilinear and bicubic methods. However, I have heard of the lanczos and other more sophisticated methods for even higher quality image scaling and I am very curious how they work. Could someone here explain the basic idea behind scaling an image using lanczos (both upscaling and downscaling) and why it results in higher quality? I do have a background in fourier analysis and have done some signal processing stuff in the past, but not with relation to image processing, so don't be afraid to use terms like "frequency response" and such in your answer :) EDIT: I guess what i really want to know is the concept and theory behind using a convolution filter for interpolation. (Note: i have already read the wikipedia article on lanczos resampling but it didn't have nearly enough detail for me) thanks alot!

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• Recommend an algorithms exercise book?

  - by Parappa

  I have a little book called Problems on Algorithms by Ian Parberry which is chock full of exercises related to the study of algorithms. Can anybody recommend similar books? What I am not looking for are recommendations of good books related to algorithms or the theory of computation. Introduction to Algorithms is a good one, and of course there's the Knuth stuff. Ideally I want to know of any books that are light on instructional material and heavy on sample problems. In a nutshell, exercise books. Preferably dedicated to algorithms rather than general logic or other math problems. By the way, the Parberry book does not seem to be in print, but it is available as a PDF dowload.

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• Why would an ASP.NET site become veeeeeery slow after the network connection dropped?

  - by Joon

  I have an ASP.NET 3.5 site published in IIS 7.5 on Windows Server 2008 R2 64 bit. The pages are accessed over SSL One of our testers has determined that if, during a postback, he blocks network access on his PC, and then after a few seconds reconnects, our site becomes excruciatingly slow. Like 30 seconds per page load. If he hits the refresh button in his browser it stays slow. If he closes the tab, then re-opens it, it becomes fast again. This behavior happens with both IE 8 and the latest firefox. There are no event log entries on the server when this happens My question: - Has anyone seen this same behavior? - Does anyone have a theory as to what causes it?

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• Does using web services to expose a .NET DAL add security?

  - by Jonno

  Currently my employer deploys a web application over 3 servers. DB - No public route Web Service DAL - No public route Web Server - Public route The reason for this is the theory that if the web server is compromised, they don't arrive at the DB directly, but instead arrive at the DAL box. To my mind, as the DAL box and Web Sever box - both run windows/IIS - if the public box has been compromised, the same exploit would likely work on the DAL box - therefore I do not see this as a real security benefit. I would like to propose we remove the middle machine and allow the web server to connect directly to the database. Is this middle box really a benefit?

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• Swapping UIImages causing 'unrecognized selector sent to instance' ?

  - by user158103

  Error: [__NSCFDate drawAtPoint:]: unrecognized selector sent to instance 0xd251e0 Termininating app due to uncaught exception 'NSInvalidArgumentException' Scenario: for the most part this works. But I notice this error, even on the simulator, when I swapping UIImages, slowly, but consistently. For example, I have a retained reference to a UIImage that im drawing. By the click of a picker control I am changing the face image (this occurs in another view-controller). I can consistently recreate this error by continuously changing the faces. It usually crashes at about the 4th swap or more. My theory: It's not loading the image, therefore the image reference is nil. I know ive read a bit about UIImage being cached, so I wouldnt think im running out of memory. Any ideas? Thanks!

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• Weird result with apache vs lighttpd in reverse proxy.

  - by northox

  I have an Apache server running in reverse proxy mode in front of a Tomcat java server. It handle HTTP and HTTPS and send those request back and forth to the Tomcat server on an internal HTTP port. I'm trying to replace the reverse proxy with Lighttpd. Here's the problem: while asking for the same HTTPS url, while using Apache as the reverse proxy, the Tomcat server redirect (302) to an HTTPS page but with Lighttpd it redirect to the same page in HTTP (not HTTPS). What does Lighttpd could do different in order to have a different result from the backend server? In theory, using Apache or Lighttpd server as a reverse proxy should not change anything... but it does. Any idea? I'll try to find something by sniffing the traffic on the backend tomcat server.

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• Freebase Query with "JOINS"

  - by codemonkey

  ... Yeah, yeah, I know traditional joins don't exist. I actually like the freebase query methodology in theory, just having a little trouble getting it to actually work for me : ) Anyone have a dumb-simple example of getting Freebase data via MQL that pulls from two different "tables"? In particular, I'm trying to get automotive data... so for example, pulling fields from both /automotive/model_year and /automotive/trim_year. I've read the documentation (for hours actually). There's a distinct possibility that I'm looking right at such an example somewhere and just not seeing it because my OLTP brain just doesn't comprehend what it's seeing. * Note * ... that the two "types" I'm working with above are siblings, not parent/child. Does freebase even allow joining data between sibling nodes... I see examples of queries pulling from parent/child, but not from siblings I don't think (or I've overlooked them).

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• Semantic stuff (RDF, OWL) on mobile phones - is it possible?

  - by Brian Schimmel

  I'm thinking about using semantic (web) technogies like RDF and OWL in an application on mobile devices. Currently I'm targeting android, but I'd also be interested in the possibilities on the iPhone and on J2ME. I would like to use a lib instead of implementing everything from scratch. I know that there are some libraries and frameworks like Jena, Redland, Protégé but they don't state on which platforms they are known to work. Having a dynamic object model and parsing from and to XML are must-haves for me. I'd also like to use reasoning, but I've been told it was rather computing-intensive, so that's only a nice-to-have. For all platforms mentioned, the question can be interpreted as Is it possible in theory (especially for J2ME I'm not sure) Are there libs that are known to work on those platforms? Is the performance on a mobile platform good enough for real world usage?

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• An Efficient data structure for Sorted List

  - by holydiver

  I want to save my objects according to a key in the attributes of my object in a sorted fashion. Later on I'll access these objects sequentially from max key to min key. I'll do some search tasks as well. I consider to use either AVL tree or RB Tree. As far as i know they are nearly equivalent in theory(Both have O(logn)). But in practice which one might be better in performance in my situation. And is there a better alternative than those, considering that I'll mostly do insert and sequentially access to the ds.

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• Fatal Error when using ADODB in VB6 on Windows Server 2003 SP2

  - by m.edmondson

  We've got a legacy app (VB6) which works fine on an old Windows Server 2003 box and has been for many years. Recently we've had to move it to a different physical location and in doing this we cloned the box with virtualisation and placed it elsewhere. In theory these two environments should be identical. On the new box however the app falls over when calling the RecordCount method of an ADODB.Recordset. I should say that I can successfully read the ADODB.RecordSet.Properties.Count property with no problem on the line before. The event viewer reports the following: Event Type: Error Event Source: Application Error Event Category: (100) Event ID: 1000 Date: 28/09/2012 Time: 11:15:27 User: N/A Computer: APP01 Description: Faulting application Control.exe, version 1.0.0.6, faulting module ntdll.dll, version 5.2.3790.4789, fault address 0x0002c6e4. I can only imagine there is something wrong with using ADODB within a virtualised environment. Any ideas?

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• Provide me with recources on Greibach & Chomsky Normal Form

  - by kristian Roger

  Hi, first please (bare with me)... :-( Im having a course at University ( Theory of Computation ) at first it was easy and simple BUT then we reach the context free grammer specialy the part where we should convert a grammer to Normal forms (Greibach & Chomsky) the thing that I couldnt understand so as usual I went to google and start searching for tutorials or videos I found many(tutorials not videos) but the problem that in tutorials they always explain things as if Im an expert or aware of every thing ... so can anyone please provide me with docs or links where they explaine the methods step by step ... (Please dont tell me to go back to my instructor because if he is useful I wont be asking your help ) thanx in advance

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• Missing safe control entry

  - by Stefan Hennicken

  I've got a working hello-world like webpart for my SPS3.0 I can compile, pack and deploy it using VS2008, makecab.exe and stsadm. So I know the theory of deploying sharepoint webparts. My problem: After I inserted an additional .webpart file, an elements.xml and a feature.xml to deploy the .webpart file and get knowledge about adding features to my webpart, the deployed webpart is missing its safe control entry in the web.config. But the dll can be found in the gac and my features are also deployed to the right folders. I didn't change anything in my manifest.xml especially not in it's -tag, because it definitely worked before i added my additional feature files. Can anybody help me? Should i provide you some code snippets? Thanks Stefan

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• Manually Writing the HTML in TWebBrowser

  - by nomad311

  I am using the strategy suggested here: http://cc.embarcadero.com/Item/23992 to get my HTML in the TWebBrowser, but I get a bunch of JavaScript errors when the page loads. If I click yes enough times I can see a page with no formatting and I'm guessing the page does nothing. My theory is that because the links in the HTML are relative, the browser can't load any of it. I have switch from passing the URL, 'about:blank' to the navigate function, to passing the servers home page - in the hopes that some internal mechanism will be able to generate full paths, but no luck. Any one successfully been able to manually write HTML to the TWebBrowser.

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• User reactions to WYSIWYM

  - by David

  I am trying to decide between a WYSIWYG editor (e.g. TinyMCE, CKEditor) and a WYSIWYM (What You See Is What You Mean) editor (e.g. WMD) for my web application. There is a thread on stackoverflow that compares the two approaches. I would like to know how users, particularly computer novices, have reacted to WYSIWYM editors in deployed web applications. It could be that computer novices are confused by WYSIWYM editors, preferring the immediacy of WYSIWYG; but is that born out in real-world applications? It's not theory I'm asking about here, but empirical evidence of the acceptance or otherwise of WYSIWYM.

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• Implicit parameter in Scalaz

  - by Thomas Jung

  I try to find out why the call Ø in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => Ø case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[String]{ def y = "y" } } trait Xs{ def ys[T](implicit x : X[T]) = x.y } class A extends Xs{ def z[B](implicit x : X[B]) : B = ys //the call Ø } Which produces: import X._ scala> new A().z[Int] res0: Int = 42 scala> new A().z[String] res1: String = y Is this valid? Can I achieve the same result with fewer steps?

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• If OOP makes problems with large projects, what doesn't?

  - by osca

  I learned Python OOP at school. My (good in theory, bad in practice) informatics told us about how good OOP was for any purpose; Even/Especially for large projects. Now I don't have any experience with teamwork in software development (what a pity, I'd like to program in a team) and I don't know anything about scaling and large projects either. Since some time I'm reading more and more about that object-oriented programming has (many) disadvantages when it comes to really big and important projects/systems. I got a bit confused by that as I always thought that OOP helped you keep large amounts of code clean and structured. Now why should OOP be problematic in large projects? If it is, what would be better? Functional, Declarative/Imperative?

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• How the hell do you get clients to use your bug tracking system?

  - by louism

  on larger projects i use a simple bug tracking system thats designed to be used by clients i have a lot of trouble convincing clients to use it (they send bug reports via email) does anyone have any strategies they can suggested? also, i have been playing around with a theory as to why this is the case; it goes like this: asking a client to log a bug is like taking your car to a mechanic for a service, and the mechanic hands you the engine oil and says "here, pop that in". basically, the client has paid you to do the work, logging a bug sounds too much like work, so they want you to do it thoughts? -- LM

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• Static DB Provider in ASP.NET MVC Causing Memory Leak

  - by user364685

  Hi, I have got an app I'm going to write in ASP.NET MVC and I want to create a DatabaseFactory object something like this:- public class DatabaseFactory { private string dbConn get { return <gets from config file>; } public IDatabaseTableObject GetDatabaseTable() { IDatabaseTableObject databaseTableObject = new SQLDatabaseObject(dbConn); return databaseTableObject; } } and this works fine, but I obviously have to instantiate the DatabaseFactory in every controller that needs it. If I made this static, so I could, in theory just call DatabaseFactory.GetDatabaseTable() it would cause a memory leak, wouldn't it?

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• PHP - Resize an image and fill gaps of proportions with a color

  - by Kerry

  I am uploading logos to my system, and they need to fix in a 60x60 pixel box. I have all the code to resize it proportionately, and that's not a problem. My 454x292px image becomes 60x38. The thing is, I need the picture to be 60x60, meaning I want to pad the top and bottom with white each (I can fill the rectangle with the color). The theory is I create a white rectangle, 60x60, then I copy the image and resize it to 60x38 and put it in my white rectangle, starting 11px from the top (which adds up to the 22px of total padding that I need. I would post my code but it's decently long, though I can if requested. Does anyone know how to do this or can you point me to code/tutorial that does this?

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• Dealing with passwords securely

  - by Krt_Malta

  Hi I have a Java web service and a Java web client making use of this service. One of the functions is to create a new user account. My two concerns are: How will I send the user's password securely from the client. How will I store the user's password securely on the server. How can I achieve these? I know the theory basically behind security, security algorithms etc but can anyone give me some advice on how I should go about in coding? Could anyone point me to some good (and if possible not complicated) examples to follow since I found some examples on the Internet very contorted? Thanks a lot and regards, Krt_Malta

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• Simulating a belongs_to_many in rails

  - by DavidP6

  I have a situation where in theory I would need to use a belongs_to_many relationship. I have an Example model and a Sentence model. Each example object has one sentence but these sentences are not necessarily unique. So, for example, I could have two example models that each have one sentence that is the same sentence. I'm not sure how to go about doing this in rails. I tried using has_and_belongs_to_many, but ran into problems. It seems that I only need the belongs_to :many part of that relationship. Ideally it would look something like this, but I know there is no belongs_to :many. Example has_one :sentence end Sentence belongs_to_many :examples end

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• Upsert - Efficient Update or Insert in VB.Net, SQL Server

  - by HK1

  I'm trying to understand how to streamline the process of inserting a record if none exists or updating a record if it already exists. I'm not using stored procedures, although maybe that would be the most efficient way of doing this. The actual scenario in which this is necessary is saving a user preference/setting to my SettingsUser table. In MS Access I would typically pull a DAO recordset looking for the specified setting. If the recordset comes back empty then I know I need to add a new record which I can do with the same recordset object. On the other hand, if it isn't empty, I can just update the setting's value right away. In theory, this is only two database operations. What is the recommended way of doing this in .NET?

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• Perl: calculating a delta of years from a date

  - by Spiros

  Hello, I am trying to figure out a way to calculate the year of birth for records when given the age to two decimals at a given date - in Perl. To illustrate this example consider these two records: date, age at date 25 Nov 2005, 74.23 21 Jan 2007, 75.38 What I want to do is get the year of birth based on those records - it should be, in theory, consistent. The problem is that when I try to derive it by calculating the difference between the year in the date field minus the age, I run into rounding errors making the results look wrong while they are in fact correct. I have tried using some "clever" combination of int() or sprintf() to round things up but to not avail. I have looked at Date::Calc but cant see something I can use. p.s. As many dates are pre-1970, I cannot not unfortunately use UNIX epoch for this.

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• How to put 1000 lightweight server applications in the cloud

  - by Dan Bird

  The company I work for sells a commercial desktop/server app that runs on any non dedicated Windows PC or server and uses Tomcat for all interactions with the application. Customers are asking that we host their instance of the application so they don't have to run it locally on their own servers. The app is lightweight and an average server, in theory, could handle 25-50 instances before users would notice a slowdown. However only 1 instance can run per Windows instance (because the application writes to a common registry branch) so we'd need something like VMWare to create 25-50 Windows instances. We know we eventually need to reprogram to make it truly cloud-worthy but what would you recommend for a server farm or whatever for this? We don't have the setup to purchase our own servers so we must use a 3rd party. We have budgeted $500 - $1000 per year per customer for this service. Thanks in advance for your suggestions, experiences and guidance.

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• How secure is a PostgreSQL database if my server is stolen?

  - by orokusaki

  If I have a server with a database if top secret data in PostgreSQL and my password is practically impossible to crack (128 character string of all sorts of weird chars, generated by hand). The server password is also uncrackable in theory (basically, ignore the possibility of a password crack on the DB). Aside from a password crack, how easy is it to get the data out of this database? Assumptions: Only the DB exists on the server. There is no password in a PHP script or anything like that The person who has the server is a computer / DB / hard-drive recovery expert I'm not using any hard-drive encryption or anything out of the norm for protection I'm trying to understand the risks involved with somebody gaining physical access to my server's hard-drives.

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