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  • Information Gain and Entropy

    - by dhorn
    I recently read this question regarding information gain and entropy. I think I have a semi-decent grasp on the main idea, but I'm curious as what to do with situations such as follows: If we have a bag of 7 coins, 1 of which is heavier than the others, and 1 of which is lighter than the others, and we know the heavier coin + the lighter coin is the same as 2 normal coins, what is the information gain associated with picking two random coins and weighing them against each other? Our goal here is to identify the two odd coins. I've been thinking this problem over for a while, and can't frame it correctly in a decision tree, or any other way for that matter. Any help? EDIT: I understand the formula for entropy and the formula for information gain. What I don't understand is how to frame this problem in a decision tree format. EDIT 2: Here is where I'm at so far: Assuming we pick two coins and they both end up weighing the same, we can assume our new chances of picking H+L come out to 1/5 * 1/4 = 1/20 , easy enough. Assuming we pick two coins and the left side is heavier. There are three different cases where this can occur: HM: Which gives us 1/2 chance of picking H and a 1/4 chance of picking L: 1/8 HL: 1/2 chance of picking high, 1/1 chance of picking low: 1/1 ML: 1/2 chance of picking low, 1/4 chance of picking high: 1/8 However, the odds of us picking HM are 1/7 * 5/6 which is 5/42 The odds of us picking HL are 1/7 * 1/6 which is 1/42 And the odds of us picking ML are 1/7 * 5/6 which is 5/42 If we weight the overall probabilities with these odds, we are given: (1/8) * (5/42) + (1/1) * (1/42) + (1/8) * (5/42) = 3/56. The same holds true for option B. option A = 3/56 option B = 3/56 option C = 1/20 However, option C should be weighted heavier because there is a 5/7 * 4/6 chance to pick two mediums. So I'm assuming from here I weight THOSE odds. I am pretty sure I've messed up somewhere along the way, but I think I'm on the right path! EDIT 3: More stuff. Assuming the scale is unbalanced, the odds are (10/11) that only one of the coins is the H or L coin, and (1/11) that both coins are H/L Therefore we can conclude: (10 / 11) * (1/2 * 1/5) and (1 / 11) * (1/2) EDIT 4: Going to go ahead and say that it is a total 4/42 increase.

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  • Understanding Haskell's filter

    - by dmindreader
    I understand that Haskell's filter is a high order function (meaning a function that takes another function as a parameter) that goes through a list checking which element fulfills certain boolean condition. I don't quite understand its definition: filter:: (a->Bool)->[a]->[a] filter p [] = [] filter p (x:y) | p x = x:filter p y | otherwise = filter p y I understand that if I pass an empty list to the function, it would just return an empty list, but how do I read the last two lines?

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  • Worst side effects from chars signedness. (Explanation of signedness effects on chars and casts)

    - by JustSmith
    I frequently work with libraries that use char when working with bytes in C++. The alternative is to define a "Byte" as unsigned char but that not the standard they decided to use. I frequently pass bytes from C# into the C++ dlls and cast them to char to work with the library. When casting ints to chars or chars to other simple types what are some of the side effects that can occur. Specifically, when has this broken code that you have worked on and how did you find out it was because of the char signedness? Lucky i haven't run into this in my code, used a char signed casting trick back in an embedded systems class in school. I'm looking to better understand the issue since I feel it is relevant to the work I am doing.

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  • Which parts of Graphics Pipelines are done using CPU & GPU?

    - by afriza
    Which parts of pipelines are done using CPU and which are done using GPU? Reading Wikipedia on Graphics Pipeline, maybe my question does not precisely represent what I am asking. Referring to this question, which "steps" are done in CPU and which are done in GPU? Edit: My question is more into which parts of logical high level steps needed to display terrain+3D models are using CPU/GPU instead of which functions.

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  • Sorting a list of colors in one dimension?

    - by Ptah- Opener of the Mouth
    I would like to sort a one-dimensional list of colors so that colors that a typical human would perceive as "like" each other are near each other. Obviously this is a difficult or perhaps impossible problem to get "perfectly", since colors are typically described with three dimensions, but that doesn't mean that there aren't some sorting methods that look obviously more natural than others. For example, sorting by RGB doesn't work very well, as it will sort in the following order, for example: (1) R=254 G=0 B=0 (2) R=254 G=255 B=0 (3) R=255 G=0 B=0 (4) R=255 G=255 B=0 That is, it will alternate those colors red, yellow, red, yellow, with the two "reds" being essentially imperceivably different than each other, and the two yellows also being imperceivably different from each other. But sorting by HLS works much better, generally speaking, and I think HSL even better than that; with either, the reds will be next to each other, and the yellows will be next to each other. But HLS/HSL has some problems, too; things that people would perceive as "black" could be split far apart from each other, as could things that people would perceive as "white". Again, I understand that I pretty much have to accept that there will be some splits like this; I'm just wondering if anyone has found a better way than HLS/HSL. And I'm aware that "better" is somewhat arbitrary; I mean "more natural to a typical human". For example, a vague thought I've had, but have not yet tried, is perhaps "L is the most important thing if it is very high or very low", but otherwise it is the least important. Has anyone tried this? Has it worked well? What specifically did you decide "very low" and "very high" meant? And so on. Or has anyone found anything else that would improve upon HSL? I should also note that I am aware that I can define a space-filling curve through the cube of colors, and order them one-dimensionally as they would be encountered while travelling along that curve. That would eliminate perceived discontinuities. However, it's not really what I want; I want decent overall large-scale groupings more than I want perfect small-scale groupings. Thanks in advance for any help.

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  • How can I transition from a front-end career to back-end career?

    - by jexx2345
    Hello, In 2004, I received my B.S. in Computer Science using mostly Java for programming. Since then, I have been hired for purely front-end positions in large companies through recruiters, doing primarily HTML/CSS, Javascript/jQuery, and OOP Actionscript 3. While I definitely have respect for the front-end, and have learned much, I feel very unfulfilled and would love to move into back-end for the more complex programming I was doing in school. My target platform of choice is ASP.Net 3.5 (C#). With a resume that has absolutely no .Net or back-end experience, how can I transition into a junior back-end job? I am currently freelancing a .Net e-commerce site, and plan to build a portfolio showcasing some apps (e-commerce mvc, blog, etc), while learning the technology. Is having a Bachelors in CS enough or should I look into getting .Net certified? Is showing course-work still relevant to an employer even though it was from 6 years ago? Thank you

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  • Does the order of columns matter in a group by clause?

    - by Jeff Meatball Yang
    If I have two columns, one with very high cardinality and one with very low cardinality (unique # of values), does it matter in which order I group by? Here's an example: select dimensionName, dimensionCategory, sum(someFact) from SomeFact f join SomeDim d on f.dimensionKey = d.dimensionKey group by d.dimensionName, -- large number of unique values d.dimensionCategory -- small number of unique values Are there situations where it matters?

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  • WordPress MU: Login from main page but not individual blogs

    - by bradrhine
    I recently upgraded to WPMU 2.8.6 and ever since, my users can't log in on their individual blogs, but they can log in from the main page. My site is at blogs.mtwp.net (we're a school district). So if a user goes to blogs.mtwp.net/BLOGNAME/wp-login.php, their password is rejected. If they go toblogs.mtwp.net/wp-login.php, they can log in and get to the dashboard from there. But it's not all users. Site admins can get in just fine. We're using wpDirAuth 1.4 if that makes a difference. Honestly, I'm stumped. Any help would be very much appreciated. Thanks!

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  • Can I get a PTypeInfo from a string?

    - by Mason Wheeler
    This is probably going to be a "no", but is there any way I can use Delphi's RTTI, either old-school or the 2010 extended RTTI, to pass in a string containing the name of a type, specifically the name of an enumerated type, and have it give me the PTypeInfo for that type? I've looked through RTTI.pas and TypInfo.pas and I don't see any function that would do that, but I might have missed something. What I'm looking for: var info: PTypeInfo; begin info := GetTypeInfoFromName('TComponentStyle'); end; Or something like that. Thing is, the name of the enumerated type would be passed in; it wouldn't be known at compile time.

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  • Good SMTP server on Windows for a production server

    - by Waleed Eissa
    I'm going to have my website hosted soon on a VPS or dedicated server (with Windows 2008), so I'm trying to plan ahead. I wonder whether the built-in SMTP server that comes with IIS7 is reliable enough for a production server or should I look for an alternative? I heard good things about hmailserver and best of all it's free, do you have any experience with using the bulit-in SMTP on a high traffic website. Thanks a lot for any suggestions

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  • Conventions for modelling c programs.

    - by Hassan Syed
    I'm working with a source base written almost entirely in straight-c (nginx). It does, however, make use of rich high level programming techniques such as compile-time metaprogramming, and OOP - including run-time dispatch. I want to draw ER diagrams, UML class diagrams and UML sequence diagrams. However to have a clean mapping between the two, consistent conventions must be applied. So, I am hopping someone has some references to material that establishes or applies such conventions to similar style c-code.

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  • Is it possible to implement Separated Interface in PHP?

    - by sunwukung
    I recently asked a question regarding the resolution of dependencies between Unit of Work and Data Mapper classes: http://stackoverflow.com/questions/3012657/dependency-injection-and-unit-of-work-pattern - (which was answered by Gabor de Mooij - thx) In PoEAA, Martin Fowler suggests using Separated Interface to manage these dependencies. My question is simple - is it actually possible to implement this pattern in PHP, or is it specific to Java interfaces? I've searched high and low and it's hard to find references to this pattern anywhere outside of PoEAA.

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  • Ruby on Rails: How to find all items with a hash that contain a specific value...

    - by kingjeffrey
    Suppose I have three models: Student, SchoolClass, and DayOfWeek. There is a HABTM relationship between Student and SchoolClass, and between SchoolClass and DayOfWeek. What I'd like to do is find all school classes belonging to a given student that meet on Monday. Now I suppose I could do something like: @student = Student.find(:student_id) @student_classes = @student.school_classes.find(:all) @student_classes_on_monday = Array.new @student_classes.each do |student_class| if student_class.day_of_week.include?("Monday") @student_classes_on_monday << student_class end end But there has to be a more elegant way. Can you help me find it?

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  • Problems with .net and toolbar, menu & status bar rendermode (blue) and standard form (grey)

    - by Andrew White
    Hiya, I'm a bit of a newbie to .NET so please ignore my ignorance. If you look at the above image (a complete prototype, ignore black bits :)) you will see lovely menus, toolbars & statusbars all using windows XP render mode and in a funky blue. Look at the form, labels, checkboxes and other buttons and you see horrible old school windows grey. These components don't have a render mode. My question: is there any way to show everything in XP style or do I have to chose new components? Thx. A.

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  • How to convert pdf to png ?

    - by lisyqiao
    ( www.pdftopng.net )*PDF to PNG*Converter is the professional software that can convert PDF to PNG with high quality and fast speed. Besides, Free PDF to PNG can convert PNG to the other images like PDF to JPG, PDF to GIF, PDF to TIFF, PDF to BMP and so on. What's more, PDF to PNG can customize your output settings including output type, output color and page range etc.

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  • Surrogate key for date dimension?

    - by Navin
    There are 2 school of thoughts : Use surrogate key preferbly in the format of YYYYMMDD as this will always be sequential. Eliminate Date dimension surrogate key and use actual date instead. My Questions to experts on dimension modeling are : 1> Which design would you prefer and why ? 2> How should we handle unknown values in each of the cases, Can we simply place NULL in Fact table for unknown dates as Foreign Key can be NULL (if no why)? 3> If we need to partition fact table on date column ,how would we achieve that in case 1. I am inclined towards using actual date and using NULL to represent UNKNOWN dates in fact table , as date related validation on fact can be done without need to look in to dimension table.

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  • Need help on how to begin learning website development

    - by Golfy
    OK for the past 10 days I have been trying to figure out where to begin learning website development a dynamic one, So far everyone told me you should start with computer science and I am like What the @#$% how am I suppose to learn computer science without going to school and get a degree but I don't want a degree I just want to learn how to devlope websites. So now I am here and confused about how to put together a website. I get HTML and CSS but still have some problems designing the site now on the other had I am having trouble trying to figure out how php and database mysql is used to put together a website. I have seen videos from lynda.com and still have no Idea after I have watched the video the basic one, one that teach you the Variables, Loops, Strings ext... ok than what happens, how do you build the website with it, that is the question I am real not understand the answer to. Any help will be appreciated.

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  • ADO.NET Data Services for MySQL

    - by Shalan
    Hey! I've searched high and low for this, and no luck. Is there a way that CRUD methods for a MySQL install (Linux box) be exposed via ADO.NET WCF Data Services? I would really love to leverage this in my WPF app :) Thank u!

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  • Has the role of the Business Analyst become redundant on true Agile projects?

    - by Joanne
    On a truely agile project where the business is performing the role of the product owner, is there still a role for the Business Analyst? The product owner would do the functional testing as soon as the user story is developed and document and prioritise the user stories. In this case which I must add I haven't experienced yet and with high performing, self motivated developers I am struggling to see the role of the traditional business analyst?

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  • programmatically creating property list from json to include an array

    - by Michael Robinson
    [{"memberid":"18", "useridFK":"30", "loginName":"Johnson", "name":"Frank", "age":"23", "place":"School", },] Someone else posted a similar question but without the fact that it was coming from a JSON deserialization. Quinn had some suggestions but it was confused about where to place/replace the following code (if it's correct): NSDictionary *item1 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@" member",[NSNumber numberWithInt:3],nil] forKeys:[NSArray arrayWithObjects:@"Title",@"View",nil]]; into this: NSData *jsonData = [jsonreturn dataUsingEncoding:NSUTF32BigEndianStringEncoding]; NSError *error = nil; NSDictionary * dict = [[CJSONDeserializer deserializer] deserializeAsDictionary:jsonData error:&error]; if (dict) { rowsArray = [dict objectForKey:@"member"]; [rowsArray retain]; } My Array.plist needs to look like the following: Root: Dictionary V Rows: Array V Item 0: Dictionary Title: String 18 V Children Array V Item 0 Dictionary Title String 30 etc. Thanks in advance. Every tutorial on JSON only shows a simple array being returned, never a 2-D..It's driving me crazy trying to figure this out.

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  • How to make a button button type (custom keyboard)

    - by Forrest
    I am creating a Spanish application in C# which will help first year students at my high school. I want to create a "custom keyboard" for characters that cannot be easily typed (Á É Í Ó Ú Ñ Ü ¡ ¿ á é í ó ú ñ ü). I was just thinking of making buttons across the bottom of the screen which would add that character to the text field when pressed. I have not be able to find anything of use. Thanks in advance

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