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  • How to store generated eigen faces for future face recognition?

    - by user3237134
    My code works in the following manner: 1.First, it obtains several images from the training set 2.After loading these images, we find the normalized faces,mean face and perform several calculation. 3.Next, we ask for the name of an image we want to recognize 4.We then project the input image into the eigenspace, and based on the difference from the eigenfaces we make a decision. 5.Depending on eigen weight vector for each input image we make clusters using kmeans command. Source code i tried: clear all close all clc % number of images on your training set. M=1200; %Chosen std and mean. %It can be any number that it is close to the std and mean of most of the images. um=60; ustd=32; %read and show images(bmp); S=[]; %img matrix for i=1:M str=strcat(int2str(i),'.jpg'); %concatenates two strings that form the name of the image eval('img=imread(str);'); [irow icol d]=size(img); % get the number of rows (N1) and columns (N2) temp=reshape(permute(img,[2,1,3]),[irow*icol,d]); %creates a (N1*N2)x1 matrix S=[S temp]; %X is a N1*N2xM matrix after finishing the sequence %this is our S end %Here we change the mean and std of all images. We normalize all images. %This is done to reduce the error due to lighting conditions. for i=1:size(S,2) temp=double(S(:,i)); m=mean(temp); st=std(temp); S(:,i)=(temp-m)*ustd/st+um; end %show normalized images for i=1:M str=strcat(int2str(i),'.jpg'); img=reshape(S(:,i),icol,irow); img=img'; end %mean image; m=mean(S,2); %obtains the mean of each row instead of each column tmimg=uint8(m); %converts to unsigned 8-bit integer. Values range from 0 to 255 img=reshape(tmimg,icol,irow); %takes the N1*N2x1 vector and creates a N2xN1 matrix img=img'; %creates a N1xN2 matrix by transposing the image. % Change image for manipulation dbx=[]; % A matrix for i=1:M temp=double(S(:,i)); dbx=[dbx temp]; end %Covariance matrix C=A'A, L=AA' A=dbx'; L=A*A'; % vv are the eigenvector for L % dd are the eigenvalue for both L=dbx'*dbx and C=dbx*dbx'; [vv dd]=eig(L); % Sort and eliminate those whose eigenvalue is zero v=[]; d=[]; for i=1:size(vv,2) if(dd(i,i)>1e-4) v=[v vv(:,i)]; d=[d dd(i,i)]; end end %sort, will return an ascending sequence [B index]=sort(d); ind=zeros(size(index)); dtemp=zeros(size(index)); vtemp=zeros(size(v)); len=length(index); for i=1:len dtemp(i)=B(len+1-i); ind(i)=len+1-index(i); vtemp(:,ind(i))=v(:,i); end d=dtemp; v=vtemp; %Normalization of eigenvectors for i=1:size(v,2) %access each column kk=v(:,i); temp=sqrt(sum(kk.^2)); v(:,i)=v(:,i)./temp; end %Eigenvectors of C matrix u=[]; for i=1:size(v,2) temp=sqrt(d(i)); u=[u (dbx*v(:,i))./temp]; end %Normalization of eigenvectors for i=1:size(u,2) kk=u(:,i); temp=sqrt(sum(kk.^2)); u(:,i)=u(:,i)./temp; end % show eigenfaces; for i=1:size(u,2) img=reshape(u(:,i),icol,irow); img=img'; img=histeq(img,255); end % Find the weight of each face in the training set. omega = []; for h=1:size(dbx,2) WW=[]; for i=1:size(u,2) t = u(:,i)'; WeightOfImage = dot(t,dbx(:,h)'); WW = [WW; WeightOfImage]; end omega = [omega WW]; end % Acquire new image % Note: the input image must have a bmp or jpg extension. % It should have the same size as the ones in your training set. % It should be placed on your desktop ed_min=[]; srcFiles = dir('G:\newdatabase\*.jpg'); % the folder in which ur images exists for b = 1 : length(srcFiles) filename = strcat('G:\newdatabase\',srcFiles(b).name); Imgdata = imread(filename); InputImage=Imgdata; InImage=reshape(permute((double(InputImage)),[2,1,3]),[irow*icol,1]); temp=InImage; me=mean(temp); st=std(temp); temp=(temp-me)*ustd/st+um; NormImage = temp; Difference = temp-m; p = []; aa=size(u,2); for i = 1:aa pare = dot(NormImage,u(:,i)); p = [p; pare]; end InImWeight = []; for i=1:size(u,2) t = u(:,i)'; WeightOfInputImage = dot(t,Difference'); InImWeight = [InImWeight; WeightOfInputImage]; end noe=numel(InImWeight); % Find Euclidean distance e=[]; for i=1:size(omega,2) q = omega(:,i); DiffWeight = InImWeight-q; mag = norm(DiffWeight); e = [e mag]; end ed_min=[ed_min MinimumValue]; theta=6.0e+03; %disp(e) z(b,:)=InImWeight; end IDX = kmeans(z,5); clustercount=accumarray(IDX, ones(size(IDX))); disp(clustercount); QUESTIONS: 1.It is working fine for M=50(i.e Training set contains 50 images) but not for M=1200(i.e Training set contains 1200 images).It is not showing any error.There is no output.I waited for 10 min still there is no output. I think it is going infinite loop.What is the problem?Where i was wrong? 2.Instead of running the training set everytime how eigen faces generated are stored so that stored eigen faces are used for future face recoginition for a new input image.So it reduces wastage of time.

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  • Is there a clean separation of my layers with this attempt at Domain Driven Design in XAML and C#

    - by Buddy James
    I'm working on an application. I'm using a mixture of TDD and DDD. I'm working hard to separate the layers of my application and that is where my question comes in. My solution is laid out as follows Solution MyApp.Domain (WinRT class library) Entity (Folder) Interfaces(Folder) IPost.cs (Interface) BlogPosts.cs(Implementation of IPost) Service (Folder) Interfaces(Folder) IDataService.cs (Interface) BlogDataService.cs (Implementation of IDataService) MyApp.Presentation(Windows 8 XAML + C# application) ViewModels(Folder) BlogViewModel.cs App.xaml MainPage.xaml (Contains a property of BlogViewModel MyApp.Tests (WinRT Unit testing project used for my TDD) So I'm planning to use my ViewModel with the XAML UI I'm writing a test and define my interfaces in my system and I have the following code thus far. [TestMethod] public void Get_Zero_Blog_Posts_From_Presentation_Layer_Returns_Empty_Collection() { IBlogViewModel viewModel = _container.Resolve<IBlogViewModel>(); viewModel.LoadBlogPosts(0); Assert.AreEqual(0, viewModel.BlogPosts.Count, "There should be 0 blog posts."); } viewModel.BlogPosts is an ObservableCollection<IPost> Now.. my first thought is that I'd like the LoadBlogPosts method on the ViewModel to call a static method on the BlogPost entity. My problem is I feel like I need to inject the IDataService into the Entity object so that it promotes loose coupling. Here are the two options that I'm struggling with: Not use a static method and use a member method on the BlogPost entity. Have the BlogPost take an IDataService in the constructor and use dependency injection to resolve the BlogPost instance and the IDataService implementation. Don't use the entity to call the IDataService. Put the IDataService in the constructor of the ViewModel and use my container to resolve the IDataService when the viewmodel is instantiated. So with option one the layers will look like this ViewModel(Presentation layer) - Entity (Domain layer) - IDataService (Service Layer) or ViewModel(Presentation layer) - IDataService (Service Layer)

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  • Why was Python's popularity so sudden? [closed]

    - by Eric Wilson
    Python first appeared in 1991, but it was somewhat unknown until 2004, if the TIOBE rankings quantify anything meaningful. What happened? What caused the interest in this 13 year old language to go through the roof? Is there a reason that Python wasn't considered a real competitor to Perl in its first decade of existence? Is there a reason that Python didn't continue in relative obscurity for another ten years? I personally think that Python is a very nice language, and I'm glad that I'm not the only one. But it doesn't have corporate backing or a killer feature that would explain a sudden rise to relevance. Does anyone know the story?

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  • How to incorporate existing open source software from a licensing perspective?

    - by Matt
    I'm working on software that uses the following libraries: Biopython SciPy NumPy All of the above have licenses similar to MIT or BSD. Three scenarios: First, if I don't redistribute those dependencies, and only my code, then all I need is my own copyright and license (planing on using the MIT License) for my code. Correct? What if I use py2exe or py2app to create a binary executable to distribute so as to make it easy for people to run the application without needing to install python and all the dependencies. Of course this also means that my binary file(s) contains python itself (along with any other packages I might have performed a pip install xyz). What if I bundle Biopython, SciPy, and NumPy binaries in my package? In the latter two cases, what do I need to do to comply with copyright laws.

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  • Is my use case diagram correct?

    - by Dummy Derp
    NOTE: I am self studying UML so I have nobody to verify my diagrams and hence I am posting here, so please bear with me. This is the problem I got from some PDF available on Google that simply had the following problem statement: Problem Statement: A library contains books and journals. The task is to develop a computer system for borrowing books. In order to borrow a book the borrower must be a member of the library. There is a limit on the number of books that can be borrowed by each member of the library. The library may have several copies of a given book. It is possible to reserve a book. Some books are for short term loans only. Other books may be borrowed for 3 weeks. Users can extend the loans. 1. Draw a use case diagram for a library. 2. Give a use case description for two use cases: • Borrow copy of book • Extend loan Diagram: Use case description: 1. Borrow a copy of the book: If the person wishes to borrow a book from Derpville Public Library, he/she must be a member of the library in which case they will be allowed to issue a certain number of books. If the person is not a member, the book will not be issued to them for taking away, rather they will have to sit and read in the library. 2. Extending loan: Some books will be lent for 3 weeks while others will be lent for more than 3 weeks in which case the person borrowing has to come to the library and get the date extended. There is a limit on how much the user can extend the date of a particular book.

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  • Are there advantages to using a DVCS for a solo developer?

    - by SnOrfus
    Right now, I use visual svn on my server, and have ankhsvn/tortoise on my personal machine. It works fine enough, and I don't have to change, but if I can see some benefits of using a DVCS, then I might give it a go. However, if there's no point or difference using it without other people, then I won't bother. So again, I ask, are there any benefits to using a DVCS when you're the only developer?

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  • RMS java web framework

    - by Kamil Tomšík
    We're currently reconsidering technologies and frameworks to get more agile with "simple" RMS CRUD-based projects. In short, short-living things like this Right now we have custom extension on top of SmartGWT but after some time it has proven not to be enough flexible. I also personally dislike that java-js compilation process and the whole GWT codebase. Not only its ugly designed, it also makes certain low-level js things very complicated if not completely impossible. So what I'm looking for is: closest to web as possible, like JSF or possibly Tapestry, it is very important to be able get "low" and weave framework if necessary. Happens more often than we thought. datagrid capable - Ext.js & PrimeFaces looks pretty good, Vaadin does too. db-schema generators (optional, no matter in which way) If it were only on me, I'd probably stick to Ext.js + custom rest-based java solution, possibly generated from database schema (not sure about concrete tooling yet) I only does have experience with vanilla Ext.js, vanilla GWT and JSF 2.0 / Seam, so it kinda hard for me to judge or even propose other frameworks. What would be your proposition? What are the problems you've faced, what was your solution and how hard do you think it was to deal with them in "big picture"?

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  • Naming methods that do the same thing but return different types

    - by Konstantin Ð.
    Let's assume that I'm extending a graphical file chooser class (JFileChooser). This class has methods which display the file chooser dialog and return a status signature in the form of an int: APPROVE_OPTION if the user selects a file and hits Open /Save, CANCEL_OPTION if the user hits Cancel, and ERROR_OPTION if something goes wrong. These methods are called showDialog(). I find this cumbersome, so I decide to make another method that returns a File object: in the case of APPROVE_OPTION, it returns the file selected by the user; otherwise, it returns null. This is where I run into a problem: would it be okay for me to keep the showDialog() name, even though methods with that name — and a different return type — already exist? To top it off, my method takes an additional parameter: a File which denotes in which directory the file chooser should start. My question to you: Is it okay to call a method the same name as a superclass method if they return different types? Or would that be confusing to API users? (If so, what other name could I use?) Alternatively, should I keep the name and change the return type so it matches that of the other methods? public int showDialog(Component parent, String approveButtonText) // Superclass method public File showDialog(Component parent, File location) // My method

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  • Command-Query-Separation and multithreading safe interfaces

    - by Tobias Langner
    I like the command query separation pattern (from OOSC / Eiffel - basically you either return a value or you change the state of the class - but not both). This makes reasoning about the class easier and it is easier to write exception safe classes. Now, with multi threading, I run into a major problem: the separation of the query and the command basically invalidates the result from the query as anything can happen between those 2. So my question is: how do you handle command query separation in an multi-threaded environment? Clarification example: A stack with command query separation would have the following methods: push (command) pop (command - but does not return a value) top (query - returns the value) empty (query) The problem here is - I can get empty as status, but then I can not rely on top really retrieving an element since between the call of empty and the call of top, the stack might have been emptied. Same goes for pop & top. If I get an item using top, I can not be sure that the item that I pop is the same. This can be solved using external locks - but that's not exactly what I call threadsafe design.

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  • Where should SQL/DB Queries be encapsulated in a software system?

    - by Stephen Bennet
    I frequently write small applications (either web based or otherwise) that require heavy database usage. i've attempted various ways of handling where to put the actual sql queries (sort of ad-hoc ORM systems). These include: Models that build themselves up - and only allowing SQL to be inside of a model. A sort of factory style method where the models are built by a factory class that is allowed to know about SQL. A third entity that maps models based on their fields/keys into the database and generates SQL code on the fly based on this. Is there a common knowledge of which method is best? Or another way I have missed? Clearly a lot of it will be based on the context of the system itself, which for me is usually to produce lightweight tools or utility frameworks. In experimenting, I've never found any of them that feel intuitively "right" and not clunky, but I also do not want to go for a full framework such as Django or Ruby - both because the tools I create are in a variety of languages and because they usually do not warrant that level of surrounding footprint.

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  • Jr developer report bug to maybe futur boss

    - by Cryptoforce
    I applied for a Web developer job in Quebec City and they call me back for a phone interview everything went well it last for over a hours and at the end they ask me to send code simple and a portfolio but in my research about the company and their products I found a PHP error(bug) in their app. Should I tell them or I will look like a total jerk and blew my chance for a interview? I know it might sound stupid, as a Jr developer I did 2 interviews they didn't went so well and I am very interested in this position part of my question is like a big lack of confidence so to make it short should I tell them about where is the error and how to fix it? Thanks

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  • Vectorization of matlab code for faster execution

    - by user3237134
    My code works in the following manner: 1.First, it obtains several images from the training set 2.After loading these images, we find the normalized faces,mean face and perform several calculation. 3.Next, we ask for the name of an image we want to recognize 4.We then project the input image into the eigenspace, and based on the difference from the eigenfaces we make a decision. 5.Depending on eigen weight vector for each input image we make clusters using kmeans command. Source code i tried: clear all close all clc % number of images on your training set. M=1200; %Chosen std and mean. %It can be any number that it is close to the std and mean of most of the images. um=60; ustd=32; %read and show images(bmp); S=[]; %img matrix for i=1:M str=strcat(int2str(i),'.jpg'); %concatenates two strings that form the name of the image eval('img=imread(str);'); [irow icol d]=size(img); % get the number of rows (N1) and columns (N2) temp=reshape(permute(img,[2,1,3]),[irow*icol,d]); %creates a (N1*N2)x1 matrix S=[S temp]; %X is a N1*N2xM matrix after finishing the sequence %this is our S end %Here we change the mean and std of all images. We normalize all images. %This is done to reduce the error due to lighting conditions. for i=1:size(S,2) temp=double(S(:,i)); m=mean(temp); st=std(temp); S(:,i)=(temp-m)*ustd/st+um; end %show normalized images for i=1:M str=strcat(int2str(i),'.jpg'); img=reshape(S(:,i),icol,irow); img=img'; end %mean image; m=mean(S,2); %obtains the mean of each row instead of each column tmimg=uint8(m); %converts to unsigned 8-bit integer. Values range from 0 to 255 img=reshape(tmimg,icol,irow); %takes the N1*N2x1 vector and creates a N2xN1 matrix img=img'; %creates a N1xN2 matrix by transposing the image. % Change image for manipulation dbx=[]; % A matrix for i=1:M temp=double(S(:,i)); dbx=[dbx temp]; end %Covariance matrix C=A'A, L=AA' A=dbx'; L=A*A'; % vv are the eigenvector for L % dd are the eigenvalue for both L=dbx'*dbx and C=dbx*dbx'; [vv dd]=eig(L); % Sort and eliminate those whose eigenvalue is zero v=[]; d=[]; for i=1:size(vv,2) if(dd(i,i)>1e-4) v=[v vv(:,i)]; d=[d dd(i,i)]; end end %sort, will return an ascending sequence [B index]=sort(d); ind=zeros(size(index)); dtemp=zeros(size(index)); vtemp=zeros(size(v)); len=length(index); for i=1:len dtemp(i)=B(len+1-i); ind(i)=len+1-index(i); vtemp(:,ind(i))=v(:,i); end d=dtemp; v=vtemp; %Normalization of eigenvectors for i=1:size(v,2) %access each column kk=v(:,i); temp=sqrt(sum(kk.^2)); v(:,i)=v(:,i)./temp; end %Eigenvectors of C matrix u=[]; for i=1:size(v,2) temp=sqrt(d(i)); u=[u (dbx*v(:,i))./temp]; end %Normalization of eigenvectors for i=1:size(u,2) kk=u(:,i); temp=sqrt(sum(kk.^2)); u(:,i)=u(:,i)./temp; end % show eigenfaces; for i=1:size(u,2) img=reshape(u(:,i),icol,irow); img=img'; img=histeq(img,255); end % Find the weight of each face in the training set. omega = []; for h=1:size(dbx,2) WW=[]; for i=1:size(u,2) t = u(:,i)'; WeightOfImage = dot(t,dbx(:,h)'); WW = [WW; WeightOfImage]; end omega = [omega WW]; end % Acquire new image % Note: the input image must have a bmp or jpg extension. % It should have the same size as the ones in your training set. % It should be placed on your desktop ed_min=[]; srcFiles = dir('G:\newdatabase\*.jpg'); % the folder in which ur images exists for b = 1 : length(srcFiles) filename = strcat('G:\newdatabase\',srcFiles(b).name); Imgdata = imread(filename); InputImage=Imgdata; InImage=reshape(permute((double(InputImage)),[2,1,3]),[irow*icol,1]); temp=InImage; me=mean(temp); st=std(temp); temp=(temp-me)*ustd/st+um; NormImage = temp; Difference = temp-m; p = []; aa=size(u,2); for i = 1:aa pare = dot(NormImage,u(:,i)); p = [p; pare]; end InImWeight = []; for i=1:size(u,2) t = u(:,i)'; WeightOfInputImage = dot(t,Difference'); InImWeight = [InImWeight; WeightOfInputImage]; end noe=numel(InImWeight); % Find Euclidean distance e=[]; for i=1:size(omega,2) q = omega(:,i); DiffWeight = InImWeight-q; mag = norm(DiffWeight); e = [e mag]; end ed_min=[ed_min MinimumValue]; theta=6.0e+03; %disp(e) z(b,:)=InImWeight; end IDX = kmeans(z,5); clustercount=accumarray(IDX, ones(size(IDX))); disp(clustercount); Running time for 50 images:Elapsed time is 103.947573 seconds. QUESTIONS: 1.It is working fine for M=50(i.e Training set contains 50 images) but not for M=1200(i.e Training set contains 1200 images).It is not showing any error.There is no output.I waited for 10 min still there is no output. I think it is going infinite loop.What is the problem?Where i was wrong?

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  • How do I make code bound to an ORM testable?

    - by RPK
    In Test Driven Development, how do I make code bound to an ORM testable? I am using a Micro-ORM (PetaPoco) and I have several methods that interact with the database like: AddCustomer UpdateRecord etc. I want to know how to write a test for these methods. I searched YouTube for videos on writing a test for DAL, but I didn't find any. I want to know which method or class is testable and how to write a test before writing the code itself.

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  • What defines code readability?

    - by zxcdw
    It is often said that readability is perhaps the most important quality-defining measure of a given piece of code for reasons concerning maintainability, ease of understanding and use. What defines the word readable in context of program source code? What kind of definitive aspects are there to code readability? I would be grateful with code examples of readable code, along with reasoning why it is readable.

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  • Are short identifiers bad?

    - by Daniel C. Sobral
    Are short identifiers bad? How does identifier length correlate with code comprehension? What other factors (besides code comprehension) might be of consideration when it comes to naming identifiers? Just to try to keep the quality of the answers up, please note that there is some research on the subject already! Edit Curious that everyone either doesn't think length is relevant or tend to prefer larger identifiers, when both links I provided indicate large identifiers are harmful!

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  • Wisdom of using open source code in a commercial software product

    - by Mr. Jefferson
    I'm looking at using some open source code in my ASP.NET web app (specifically dapper). Management is not a fan, because open source is seen as a risk that has bitten us before. Apparently previous developers have had to rewrite things after having open-source components fail. The pros seem to be: It does a lot of stuff for me that would otherwise involve either lots of boilerplate code or Microsoft's recommended but slower solution (Entity Framework). Cons: It's complex enough that if it were to fail suddenly in production, I would be hard pressed to fix it. However, it's in use on a much higher-traffic site than mine, so I don't think it'll end up being a high risk portion of the project. What is the consensus here? Is it unwise to use open source code in my project that I don't know/understand as well as I do my own code?

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  • Is there a solution for SugarCRM that can map roles or privileges to Active Directory groups?

    - by Cory Larson
    We're presenting SugarCRM as an option to one of our clients, but they want to drive permissions within Sugar by users' AD groups. Current LDAP integration with SugarCRM only does password management. Does anybody know of a plug-in that supports this? I've searched and have not been able to find anything. Has anybody change the LDAP module code within Sugar to accommodate these features? I'd be interested in chatting with you. I apologize if this isn't on the correct site; neither serverfault nor stackoverflow seemed like the correct place. Perhaps webapps? Thanks!

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  • What is up with the Joy of Clojure 2nd edition?

    - by kurofune
    Manning just released the second edition of the beloved Joy of Clojure book, and while I share that love I get the feeling that many of the examples are already outdated. In particular, in the chapter on optimization the recommended type-hinting seems not to be allowed by the compiler. I don't know if this was allowable for older versions of Clojure. For example: (defn factorial-f [^long original-x] (loop [x original-x, acc 1] (if (>= 1 x) acc (recur (dec x) (*' x acc))))) returns: clojure.lang.Compiler$CompilerException: java.lang.UnsupportedOperationException: Can't type hint a primitive local, compiling:(null:3:1) Likewise, the chapter on core.logic seems be using an old API and I have to find workarounds for each example to accommodate the recent changes. For example, I had to turn this: (logic/defrel orbits orbital body) (logic/fact orbits :mercury :sun) (logic/fact orbits :venus :sun) (logic/fact orbits :earth :sun) (logic/fact orbits :mars :sun) (logic/fact orbits :jupiter :sun) (logic/fact orbits :saturn :sun) (logic/fact orbits :uranus :sun) (logic/fact orbits :neptune :sun) (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital))) into this, leveraging the pldb lib: (pldb/db-rel orbits orbital body) (def facts (pldb/db [orbits :mercury :sun] [orbits :venus :sun] [orbits :earth :sun] [orbits :mars :sun] [orbits :jupiter :sun] [orbits :saturn :sun] [orbits :uranus :sun] [orbits :neptune :sun])) (pldb/with-db facts (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital)))) I am still pulling teeth to get the later examples to work. I am relatively new programming, myself, so I wonder if I am naively looking over something here, or are if these points I'm making legitimate concerns? I really want to get good at this stuff like type-hinting and core.logic, but wanna make sure I am studying up to date materials. Any illuminating facts to help clear up my confusion would be most welcome.

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  • When should I make the first commit to source control?

    - by Kendall Frey
    I'm never sure when a project is far enough along to first commit to source control. I tend to put off committing until the project is 'framework-complete' and primarily commit features from then on. (I haven't done any personal projects large enough to have a core framework too big for this.) I have a feeling this isn't best practice, though I'm not sure what all could go wrong. Let's say, for example, I have a project which consists of a single code file. It will take about 10 lines of boilerplate code, and 100 lines to get the project working with extremely basic functionality (1 or 2 features). Should I first check in: The empty file? The boilerplate code? The first features? At some other point? Also, what are the reasons to check in at a specific point?

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  • Which statically typed languages support intersection types for function return values?

    - by stakx
    Initial note: This question got closed after several edits because I lacked the proper terminology to state accurately what I was looking for. Sam Tobin-Hochstadt then posted a comment which made me recognise exactly what that was: programming languages that support intersection types for function return values. Now that the question has been re-opened, I've decided to improve it by rewriting it in a (hopefully) more precise manner. Therefore, some answers and comments below might no longer make sense because they refer to previous edits. (Please see the question's edit history in such cases.) Are there any popular statically & strongly typed programming languages (such as Haskell, generic Java, C#, F#, etc.) that support intersection types for function return values? If so, which, and how? (If I'm honest, I would really love to see someone demonstrate a way how to express intersection types in a mainstream language such as C# or Java.) I'll give a quick example of what intersection types might look like, using some pseudocode similar to C#: interface IX { … } interface IY { … } interface IB { … } class A : IX, IY { … } class B : IX, IY, IB { … } T fn() where T : IX, IY { return … ? new A() : new B(); } That is, the function fn returns an instance of some type T, of which the caller knows only that it implements interfaces IX and IY. (That is, unlike with generics, the caller doesn't get to choose the concrete type of T — the function does. From this I would suppose that T is in fact not a universal type, but an existential type.) P.S.: I'm aware that one could simply define a interface IXY : IX, IY and change the return type of fn to IXY. However, that is not really the same thing, because often you cannot bolt on an additional interface IXY to a previously defined type A which only implements IX and IY separately. Footnote: Some resources about intersection types: Wikipedia article for "Type system" has a subsection about intersection types. Report by Benjamin C. Pierce (1991), "Programming With Intersection Types, Union Types, and Polymorphism" David P. Cunningham (2005), "Intersection types in practice", which contains a case study about the Forsythe language, which is mentioned in the Wikipedia article. A Stack Overflow question, "Union types and intersection types" which got several good answers, among them this one which gives a pseudocode example of intersection types similar to mine above.

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  • What happens differently when you add a task Asynchronously on GAE?

    - by Ben Grunfeld
    Google's doc on async tasks assumes knowledge of the difference between regular and asynchronously added tasks. add_async(task, transactional=False, rpc=None) Asynchronously add a Task or a list of Tasks to this Queue. How is adding tasks asynchronously different to adding them regularly. I.e. what is the difference between using add(task, transactional=False) and add_async(task, transactional=False, rpc=None) I've heard that adding tasks regularly blocks certain things. Any explanation of what it blocks and how, and how async tasks don't block would be greatly appreciated.

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  • One method with many behaviours or many methods

    - by Krowar
    This question is quite general and not related to a specific language, but more to coding best practices. Recently, I've been developing a feature for my app that is requested in many cases with slightly different behaviours. This function send emails , but to different receivers, or with different texts according to the parameters. The method signature is something like public static sendMail (t_message message = null , t_user receiver = null , stream attachedPiece = null) And then there are many condition inside the method, like if(attachedPiece != null) { } I've made the choice to do it this way (with a single method) because it prevents me to rewrite the (nearly) same method 10 times, but I'm not sure that it's a good practice. What should I have done? Write 10 sendMail method with different parameters? Are there obvious pros and cons for these different ways of programming? Thanks a lot.

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  • What's your advise on a potential legal suit? [closed]

    - by ohho
    I [xxx app developer] received an email from Apple that a developer [of yyy app] believes I am "infringing their copyright." Description of Issue: [xxx developer] copied my application (my application is [yyy]) feature by feature. Even their donation model is completely copied from my application. Their first release was significantly later than mine, which implies copying of the application rather than parallel development. I suffered significant financial losses because of their actions, in additional to promotion problems as many people are confused with their product. My advertising was based around the idea of a "free [yyy] application for an iPhone" and they have just taken that as a title for their application. I would appreciate if someone takes a look at their release schedule and compare it to my releases. Additionally, please take a look at their functionality and how it point by point copies the functionality of my older releases. I am asking Apple to remove their application from the App Store, and ban them from resubmitting it. Thank you for your time! [yyy developer], the developer of the [yyy] application. My response was: The code of [xxx] is written by myself, using Apple public API. The graphics elements are designed by myself. The user interface and app control are independently designed and different from other [similar type] apps (please judge yourself). In-app Purchase is iOS Apple standard API. iAd is Apple iOS standard API. I don't think features can be owned exclusively. In fact, my app comes with fewer features, as I prefer minimalist design. I don't think idea can be owned exclusively. Apple responded: Thank you for your response. Unfortunately, Apple cannot serve as arbiter for disputes among third parties. Please contact [yyy developer] directly regarding your actions. You can reach [yyy developer] through: [...]. We look forward to confirmation from both parties that this issue has been resolved. If this issue is not resolved shortly, Apple may be forced to pull your application(s) from the App Store. Then I sent my response above to [yyy developer]. [yyy developer] then asked me "to provide (my) legal address and contact details that (his) lawyer requires to file a copyright infringement suit." IMO, I don't think the [yyy developer]'s claim on "feature by feature" copy is valid. I have fewer features, completely different user interface design. However, I don't think I can afford a legal action for an app of so little financial return. So what's your advise on this? Should I just let Apple pull my app? Or is there any alternative I can consider? FYI ... UI of [xxx app]: and UI of [yyy app]:

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  • Best Software Development Methodology Environment for Fresh Graduates

    - by newbie
    I am looking online for IT-related jobs and most of the time, they are indicating the need that the candidate must have an experience in certain software development methodology (SCRUM, RAD, Waterfall, Agile, etc). Truly, different companies have different needs. What do you think is the best environment / software development methodology for a fresh graduate to be part of so that they could really be a good programmer? What will be avoided?

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  • Web Developer interview questions

    - by Baba
    I read an article today that listed some basic questions about web development: Describe how POST data was submitted to a server by a browser. Explain a number of HTTP status codes (except maybe 404 and 500). Explain SOLID or name a design pattern. Explain ways to improve a page load speed or user experience. The author says "if you can’t answer the questions above there are a lot of people who wouldn’t think of you as a Senior Web Developer." My questions are: How relevant are these questions in respect to real life web programming and scalability? How true is that statement? In other words, do you consider this knowledge a requirement to be considered a Senior Web Developer? I was able to answer all the questions, too easily it seemed, so I'm wondering whether it is effective to use these or similar questions to screen developers rather than asking them to write sample code.

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