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• Parameter Tuning for Perceptron Learning Algorithm

  - by Albert Diego

  Hi, I'm having sort of an issue trying to figure out how to tune the parameters for my perceptron algorithm so that it performs relatively well on unseen data. I've implemented a verified working perceptron algorithm and I'd like to figure out a method by which I can tune the numbers of iterations and the learning rate of the perceptron. These are the two parameters I'm interested in. I know that the learning rate of the perceptron doesn't affect whether or not the algorithm converges and completes. I'm trying to grasp how to change n. Too fast and it'll swing around a lot, and too low and it'll take longer. As for the number of iterations, I'm not entirely sure how to determine an ideal number. In any case, any help would be appreciated. Thanks.

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• Weird behaviour with vector::erase and std::remove_if with end range different from vector.end()

  - by Edison Gustavo Muenz

  Hi, I need to remove elements from the middle of a std::vector. So I tried: struct IsEven { bool operator()(int ele) { return ele % 2 == 0; } }; int elements[] = {1, 2, 3, 4, 5, 6}; std::vector<int> ints(elements, elements+6); std::vector<int>::iterator it = std::remove_if(ints.begin() + 2, ints.begin() + 4, IsEven()); ints.erase(it, ints.end()); After this I would expect that the ints vector have: [1, 2, 3, 5, 6]. In the debugger of Visual studio 2008, after the std::remove_if line, the elements of ints are modified, I'm guessing I'm into some sort of undefined behaviour here. So, how do I remove elements from a Range of a vector?

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• (My)SQL performance: updating one field vs many unneccesary fields

  - by changokun

  i'm processing a form that has a lot of fields for a user who is editing an existing record. the user may have only changed one field, and i would typically do an update query that sets the values of all the fields, even though most of them don't change. i could do some sort of tracking to see which fields have actually changed, and only update the few that did. is there a performance difference between updating all fields in a record vs only the one that changed? are there other reasons to go with either method? the shotgun method is pretty easy...

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• Making your class an event source in Java

  - by Crystal

  I'm making a custom button in Java that has two states, mousePressed, and mouseReleased. At the same time, if I wanted to reuse this button, so that other event listeners can register with it, are these the appropriate steps I should do: override addActionListener(ActionListener action) override removeActionListener(ActionListener action) have a private variable like List <ActionListener> list = new List <ActionListener>() to keep track of when events get added and some sort of function with for loop to run all the actions: public void runListeners() { for (ActionListener al : list) { al.actionPerfomed; } } I'm not really sure if this is the way you can do it or if there are other things I am missing. Like does my custom class have to be implements ActionListener? Thanks.

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• Are there any widely-agreed upon guidelines for rating your language knowledge on a scale?

  - by DVK

  The question was imagined after a co-worker was complaining for an hour about some guy who could not answer basic Java questions on an interview after self-identifying himself as "8 out of 10" on Java. While that was an obvious fib, I personally always had major trouble defining my specific language skills on a sliding scale unless I'm given specific guidelines (remember 40 standard libraries by heart? Able to solve 10 random Project Euler problems in <30 mins each? Can write implementation of A, B and C data-structures from scratch in 30 mins? Know 30% of standard? Can answer 50% of questions on StackOverflow pertaining to the language?) So, I was wondering - is there some sort of commonly accepted methodology for translating such tangible benchmarks into "rate yourself on a language between 1-10"? "Kernighan gets an A, God gets a B, everyone else gets C and less" type jokes are not helpful :)

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• What ways are there for cleaning an R environment from objects?

  - by Tal Galili

  I know I can use ls() and rm() to see and remove objects that exist in my environment. However, when dealing with "old" .RData file, one needs to sometimes pick an environment a part to find what to keep and what to leave out. What I would like to do, is to have a GUI like interface to allow me to see the objects, sort them (for example, by there size), and remove the ones I don't need (for example, by a check-box interface). Since I imagine such a system is not currently implemented in R, what ways do exist? What do you use for cleaning old .RData files? Thanks, Tal

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• A maximum character limit on the preg functions?

  - by animuson

  On my site I use output buffering to grab all the output and then run it through a process function before sending it out to the browser (I don't replace anything, just break it into more manageable pieces). In this particular case, there is a massive amount of output because it is listing out a label for every country in the database (around 240 countries). The problem is that in full, my preg_match functions seems to get skipped over, it does absolutely nothing and returns no matches. However, if I remove parts of the labels (no particular part, just random pieces to reduce characters) then the preg_match functions works again. It doesn't seem to matter what I remove from the label, it just seems to be that as long as I remove so many characters. Is there some sort of cap on what the preg functions can handle or will it time out if there is too much data to be scanned over?

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• C++/MFC: Handling multiple CListCtrl's headers HDN_ITEMCLICK events

  - by raph.amiard

  I'm coding an MFC application in which i have a dialog box with multiple CListCtrls in report view. I want one of them to be sortable. So i handled the HDM_ITEMCLICK event, and everything works just fine .. Except that if i click on the headers of another CListCtrl, it does sort the OTHER CListCtrl, which does look kind of dumb. This is apparently due to the fact that headers have an ID of 0, which make the entry in the message map look like this : ON_NOTIFY(HDN_ITEMCLICK, 0, &Ccreationprogramme::OnHdnItemclickList5) But since all the headers have an id of zero, apparently every header of my dialog sends the message. Is there an easy way around this problem ?

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• How, exactly does HTML5's GeoLocation work?

  - by Dan

  I know the browser shares my IP address and details of nearby wireless networks to determine my location, but what sort of info does it know about nearby wifi networks? For example, where I live are no public wireless networks, and from my home I can see about 5 private networks, yet my location is determined within 20 meters. With there being no open networks nearby, how does Google determine my location? The only way I can think of is that Google mapped the locations of all wireless networks when they mapped streets for Street View. I've searched about online, but all I can't find any specific details.

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• Lucene.NET - Find documents that do not contain a specified field

  - by Brandon

  Let's say I have 2 instance of a class called 'Animal'. Animal has 3 fields: Name, Age, and Type The name field is nullable, so before I insert an instance of Animal as a Lucene indexed document, I check if Animal.Name == null, and if it does, I do not insert it as a field in my document. If I were to retrieve all animals, I would see that the Name field does not exist and I can set its value to null. However, there may be situations where I want to say "Get me all animals that do not have a name specified yet." In this situation I want to retrieve all Lucene.NET documents from my animal index that do not contain the Name field. Is there an easy way to do this with Lucene.NET? I want to stay away from having to perform some sort of hack to check if my name field has a value of 'null'.

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• How to order the images in a mysql database?

  - by user305270

  Hy! Here is my problem: i have a profile and this profile has for example 100 images. When someone visit this profile the first image will be the first result of my query that sorts by updated_at. But if the user would want to put the image with the (id = 8) to be the first, then (id = 22) then (id = 88) and so on? I need to put another field or is really necessary a new table to make a custom sort on images? and maybe someone explain this to me how to do? thanks, i appreciate your help ;)

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• Rails Full Engine using a Full Engine

  - by SirLenz0rlot

  I've got this full rails engine Foo with functionality X. I want to make another engine, engine Bar, that is pretty much the same, but override funcitonality x with y. (it basically does the same, but a few controller actions and views are differently implemented). (I might split this later in several mountable engines, but for now, this will be the setup: project Baz, using engine Bar, which uses engine Foo) I would like to know if there are any pitfalls. It doesn't seem like a pattern that is often used? Anybody else using this 'some sort of engine inheritance'?

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• Rectangular BackColor of selection in RichTextBox

  - by AgentConundrum

  Background: I'm going to start studying/coding at the local university's library. Since I'm not a student, I won't be able to utilize their wireless internet access. Since StackOverflow is such a great resource, I want to be able to take it with me, so I'm building a small desktop application to load/search/display the most recent data dumps. Problem: I want to display code blocks in the same sort of rectangular block as this site does, so I played with the RichTextBox control to try to create this effect. Unfortunately, the RichTextBox.SelectedBackColor property only colors the actual text, when what I want is a rectangle reaching to the outer limits of the selection. Example: This is what I am able to produce with the RichTextBox: This is what I would like to create: Questions: Is there any way to produce this effect using the RichTextBox? If not, are there any other controls I could use to create this effect?

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• Immutability of big objects

  - by Malax

  Hi StackOverflow! I have some big (more than 3 fields) Objects which can and should be immutable. Every time I run into that case i tend to create constructor abominations with long parameter lists. It doesn't feel right, is hard to use and readability suffers. It is even worse if the fields are some sort of collection type like lists. A simple addSibling(S s) would ease the object creation so much but renders the object mutable. What do you guys use in such cases? I'm on Scala and Java, but i think the problem is language agnostic as long as the language is object oriented. Solutions I can think of: "Constructor abominations with long parameter lists" The Builder Pattern Thanks for your input!

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• COM+ Connection Pooling Doesn't Appear to be working on SQL Server 2005 Cluster

  - by kmacmahon

  We have a COM+ Data Layer that utilized Connection Pooling. Its deployed to 3 clusters, 2 SQL Server 2000 and 1 SQL Server 2005 environment. We noticed today that our monitoring software is reporting Thousands of Logins per minute on the SQL Server 2005 box. I did some tracing in both environments and profiler is reporting this for the 2000 boxes: sp_reset_connection SQL CALL sp_reset_connection SQL CALL sp_reset_connection SQL CALL and this for the 2005 box: Audit Logout sp_reset_connection Audit Login SQL CALL Audit Logout sp_reset_connection Audit Login SQL CALL Audit Logout sp_reset_connection Audit Login SQL CALL Is there some sort configuration for SQL Server 2005 different from SQL Server 2000 that we might be missing that would be creating this issue?

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• Visual Studio bug ~ quick find [CONFIRMED]

  - by drachenstern

  In Visual Studio 2010 Pro (Version 10.0.30319.1 RTMRel), I noticed tonight that for some reason I kept getting a wider window for quick find, but thought I was losing my mind. So I exited, restarted, etc to verify. Here's my repro steps Open existing project (I don't think it matters which one) Press ctrlf and give it something to search for (?) in "current document" Press enter Press ctrlf Press enter goto 4 Can you reproduce a slowly expanding quick find window? Do I have some sort of wacky bugged out system? I'ld obviously like to submit a bug report to MS if this is indeed a viable repro.

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• Generalized plugable caching pattern?

  - by BCS

  Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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• IDispatchMessageInspector to log plain-text soap messages?

  - by Dan Thomas

  I've written a WCF IDispatchMessageInspector, so I can log incomming and outgoing messages. But I'm not sure how to get a nicely-formatted XML string to log. My code looks something like this: public object AfterReceiveRequest(ref Message request, IClientChannel channel, InstanceContext instanceContext) { MessageBuffer buffer = request.CreateBufferedCopy(Int32.MaxValue); request = buffer.CreateMessage(); Log("Received", request.ToString(); return null; } The result of this logging includes things like "ampersand lt;" and some sort of binary-encoded data. How do I get something that looks like a standard soap XML document? I know this should be obvious, but I'm just too dense to figure it out. Thanks. Dan

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• extracting a quadrilateral image to a rectangle

  - by Will

  In the image below, the sign on the side of the van is not face-on to the camera. I want to calculate, as best I can with the pixels I have, what it'd look like face on. I imagine that this is some kind of loop through the x and y axis doing a Bresenham's line on both dimensions at once with some kind of mixing when pixels in the source image overlap - some sub-pixel mixing of some sort? What approaches are there, and how do you mix the pixels? Is there a standard approach for this?

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• Upgrading Visual Studio web service project says to "convert to web application."

  - by Buggieboy

  I have a Visual Studio 2003 web service project that I have to upgrade to Visual Studio 2008. After I have run the conversion wizard, I get this message: You have completed the first step in converting your Visual Studio .NET 2003 web project. To complete the conversion, please select your project in the Solution Explorer and choose the 'Convert to Web Application' context menu item. I got this message with another project, which was originally a "web site", rather than an ASP.NET "web application". It made sense to in that case (sort of). Why, however, would I not just want to have this project remain a web service project? Additionally, when I follow the instructions and select "Convert to Web Application" from the context menu, I don't get any feedback that anything has changed. Should it have? If so, what?

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• How can I tell NetBeans to use the latest available version of a JAR for a library?

  - by Freiheit

  I have a Netbeans project with a library defined which includes several JARs. These JARs are versioned like lib\blah\com.blah.wibble.jar_0.6.1.201004161543 . These are nightly builds from another project so that version changes often. I know I can point NetBeans at the specific JARs with the version name, but this means that every time I get a new version I have to update the NetBeans library. I can also strip the version name from the JARs, but this makes it hard to track down bugs. "What version of the blah JARs?" is usually the second thing we ask when we find a bug. Is it possible to tell Netbeans to use included com.blah.wibble.jar_[??????] where ???? is some sort of automatic pointer to use the latest available version?

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• Find subset with K elements that are closest to eachother

  - by Nima

  Given an array of integers size N, how can you efficiently find a subset of size K with elements that are closest to each other? Let the closeness for a subset (x1,x2,x3,..xk) be defined as: 2 <= N <= 10^5 2 <= K <= N constraints: Array may contain duplicates and is not guaranteed to be sorted. My brute force solution is very slow for large N, and it doesn't check if there's more than 1 solution: N = input() K = input() assert 2 <= N <= 10**5 assert 2 <= K <= N a = [] for i in xrange(0, N): a.append(input()) a.sort() minimum = sys.maxint startindex = 0 for i in xrange(0,N-K+1): last = i + K tmp = 0 for j in xrange(i, last): for l in xrange(j+1, last): tmp += abs(a[j]-a[l]) if(tmp > minimum): break if(tmp < minimum): minimum = tmp startindex = i #end index = startindex + K? Examples: N = 7 K = 3 array = [10,100,300,200,1000,20,30] result = [10,20,30] N = 10 K = 4 array = [1,2,3,4,10,20,30,40,100,200] result = [1,2,3,4]

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• Reducing time in C# Forms Control.set_Text(string) function

  - by awshepard

  Hoping for a quick answer (which SO seems to be pretty good for)... I just ran a performance analysis with VS2010 on my app, and it turns out that I'm spending about 20% of my time in the Control.set_Text(string) function, as I'm updating labels in quite a few places in my app. The window has a timer object (Forms timer, not Threading timer) that has a timer1_Tick callback, which updates one label every tick (to give a stop-watch sort of effect), and updates about 15 labels once each second. Does anyone have quick suggestions for how to reduce the amount of time spent updating text on a form, other than increasing the update interval? Are there other structures or functions I should be using?

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• UITableView setting standalone delegate object?

  - by fuzzygoat

  Hi have setup a sample application using a UITableView. Initially I did this by conforming my controller to and , added a tableView in IB and connected "datasource" & "delegate" to Files Owner. It all works so thats good. What I have been trying out is creating my own class for the delegate. I created a new class and added and , but quickly found I could not connect the tableViewdataSource / delegate. To solve this I added an "Object" (NSObject) in IB and set it to my new class. I then connected the dataSource and delegate outlets to this object. It sort of works, the app runs and displays the tableView, but when I try and scroll the table the app crashes. Can I ask if I am going about this the right way? gary

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