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• A detail question when applying genetic algorithm to traveling salesman

  - by burrough

  I read various stuff on this and understand the principle and concepts involved, however, none of paper mentions the details of how to calculate the fitness of a chromosome (which represents a route) involving adjacent cities (in the chromosome) that are not directly connected by an edge (in the graph). For example, given a chromosome 1|3|2|8|4|5|6|7, in which each gene represents the index of a city on the graph/map, how do we calculate its fitness (i.e. the total sum of distances traveled) if, say, there is no direct edge/link between city 2 and 8. Do we follow some sort of greedy algorithm to work out a route between 2 and 8, and add the distance of this route to the total? This problem seems pretty common when applying GA to TSP. Anyone who's done it before please share your experience. Thanks.

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• Implementing a Patricia Trie for use as a dictionary

  - by Regis Frey

  I'm attempting to implement a Patricia Trie with the methods addWord(), isWord(), and isPrefix() as a means to store a large dictionary of words for quick retrieval (including prefix search). I've read up on the concepts but they just aren't clarifying into an implementation. I want to know (in Java or Python code) how to implement the Trie, particularly the nodes (or should I implement it recursively). I saw one person who implemented it with an array of 26 child nodes set to null/None. Is there a better strategy (such as treating the letters as bits) and how would you implement it?

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• HTML5 web storage: can different websites overwrite each other’s data on a user’s computer?

  - by Deepak Mahalingam

  I have a few questions regarding the concept of HTML5 storage. I went through the w3c specification, books and tutorials on the same, but still I am a bit unclear about certain concepts: Assume that I access Website A. Some JavaScript runs in my browser that sets a key value pair, say ('username','deepak'). Then I access Website B which also adds a key,value pair in the localstorage as ('username','mahalingam'). How will they both be differentiated? Will Website B override the value set by website A in my localstorage? How can we ensure that a website would not erase all of my localstorage?

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• Difference of HTTP Components, Restlet, Apache Mina and Netty

  - by dexter

  I used HTTPComponents to implement a custom web server that access SQLite database. Requests are sent via TCP/IP and I am using REST concepts. By the way my frontend is HTML/jQuery. I know it will be a lot easier if I'll just create a servlet but I am restricted to just using apache http server. I really don't get good performance in using HTTP Components. Any suggestions please. Thanks in advance.

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• Static and Non Static Method Intercall in Java

  - by Vishal

  I am clearing my concepts on Java. My knowledge about Java is on far begineer side, so kindly bear with me. I am trying to understand static method and non static method intercalls. I know -- Static method can call another static method simply by its name within same class. Static method can call another non staic method of same class only after creating instance of the class. Non static method can call another static method of same class simply by way of classname.methodname - No sure if this correct ? My Question is about non static method call to another non staic method of same class. In class declaration, when we declare all methods, can we call another non static method of same class from a non static class ? Please explain with example. Thank you.

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• Psuedo-Backwards Builder Pattern?

  - by Avid Aardvark

  In a legacy codebase I have a very large class with far too many fields/responsibilities. Imagine this is a Pizza object. It has highly granular fields like: hasPepperoni hasSausage hasBellPeppers I know that when these three fields are true, we have a Supreme pizza. However, this class is not open for extension or change, so I can't add a PizzaType, or isSupreme(), etc. Folks throughout the codebase duplicate the same "if(a && b && c) then isSupreme)" logic all over place. This issue comes up for quite a few concepts, so I'm looking for a way to deconstruct this object into many subobjects, e.g. a pseudo-backwards Builder Pattern. PizzaType pizzaType = PizzaUnbuilder.buildPizzaType(Pizza); //PizzaType.SUPREME Dough dough = PizzaUnbuilder.buildDough(Pizza); Is this the right approach? Is there a pattern for this already? Thanks!

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• forloop and table in latex

  - by Tim

  Hi, Here is the latex code for my table: \begin{table}{| c || c | c | c || c | c | c | } \caption{Examples of the concepts. \label{tab:conceptsimgs}}\\ \hline \backslashbox{Concept}{Class} &\multicolumn{3}{|c||}{Negative Class} & \multicolumn{3}{|c|}{Positive Class} \\ \hline \forloop{themenumber}{1}{\value{themenumber} < 4}{ %\hline \arabic{themenumber} \forloop{classnumber}{0}{\value{classnumber} < 2}{ \forloop{imagenumber}{1}{\value{imagenumber} < 4}{ & 0 } } \\ \hline } \end{table} Something is wrong in the result however. There is some extra thing at the end of the table, as shown in this image. How can I fix it? Thanks and regards!

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• backslashbox is too wide

  - by Tim

  Hi I feel the first column in my longtable is too wide. Please see the figure below My code is: \begin{center} \begin{longtable}{|c|c|c|c|c|c|} \caption{Error rates for SVM and 100 random counts. \label{tab:svmcount100errortable}}\\ \hline \backslashbox{Concepts}{Train sizes} & 10 & 100 & 1000 & 10000 & 100000\\ \hline 1 & 0.49 (0.00) & 0.49 (0.00) & 0.47 (0.00) & 0.43 (0.00) & 0.33 (0.00)\\ \hline \end{longtable} \end{center} I wonder if there is some way to reduce the width of the first column? Thanks and regards!

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• Starting point for learning CAD/CAE file formats?

  - by Escader

  We are developing some stress and strain analysis software at university. Now it's time to move from rectangles and boxes and spheres to some real models. But I still have little idea where to start. In our software we are going to build mesh and then make calculations, but how do I import solid bodies from CAD/CAE software? 1) How CAD/CAE models are organised? How solid bodies are represented? What are the possibilities of DWG, DXF, IGES, STEP formats? There is e.g. a complete DXF reference, but it's too difficult for me to understand without knowing basic concepts. 2) Are there C++ libraries to import solid bodies from CAD/CAE file formats? Won't it be too difficult to build a complete model to be able to import comprehensive file?

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• Java Concurrency: CAS vs Locking

  - by Hugo Walker

  Im currently reading the Book Java Concurrency in Practice. In the Chapter 15 they are speaking about the Nonblocking algorithms and the compare-and-swap (CAS) Method. It is written that the CAS perform much better than the Locking Methods. I want to ask the people which already worked with both of this concepts and would like to hear when you are preferring which of these concept? Is it really so much faster? Personally for me the usage of Locks is much clearer and easier to understand and maybe even better to maintain. (Please correct me if I am wrong). Should we really focus creating our concurrent code related on CAS than Locks to get a better performance boost or is sustainability a higher thing? I know there is maybe not a strict rule, when to use what. But I just would like to hear some opinions, experiences with the new concept of CAS.

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• What is the relaxation condition in graph theory

  - by windopal

  Hi, I'm trying to understand the main concepts of graph theory and the algorithms within it. Most algorithms seem to contain a "Relaxation Condition" I'm unsure about what this is. Could some one explain it to me please. An example of this is dijkstras algorithm, here is the pseudo-code. 1 function Dijkstra(Graph, source): 2 for each vertex v in Graph: // Initializations 3 dist[v] := infinity // Unknown distance function from source to v 4 previous[v] := undefined // Previous node in optimal path from source 5 dist[source] := 0 // Distance from source to source 6 Q := the set of all nodes in Graph // All nodes in the graph are unoptimized - thus are in Q 7 while Q is not empty: // The main loop 8 u := vertex in Q with smallest dist[] 9 if dist[u] = infinity: 10 break // all remaining vertices are inaccessible from source 11 remove u from Q 12 for each neighbor v of u: // where v has not yet been removed from Q. 13 alt := dist[u] + dist_between(u, v) 14 if alt < dist[v]: // Relax (u,v,a) 15 dist[v] := alt 16 previous[v] := u 17 return dist[] Thanks

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• Spring MVC Web PetClinic Tutorial?

  - by wuntee

  Is there a tutorial that goes along with the PetClinic application? I have been trying to find one, but google is not helping me today. Specifically, I dont understand things like: @Autowired - what does that even mean? @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } How can a request return just a string? Shouldnt it need to return some sort of ModelAndView? Or does the application somehow redirect to whatever is returned? A lot of confusing concepts - if there is a tutorial, or video (like spring-security has) that would be very helpful. Thanks.

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• Which programming languages have helped you to understand programming better?

  - by Xaisoft

  Which programming languages not only make you more proficient in the particular language your are learning, but also have a direct impact on the way you think and understand programming in general; therefore, making you a better programmer in other languages. Basically, which languages have the biggest impact on understanding the how and why of different programming concepts? What about Scheme? I have heard good things about that. I thought about taking the simplest of problems and implementing them in various languages. Has anyone done this?

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• Practical guide to programming paradigms ?

  - by Pierre

  I think I might be misunderstanding the whole thing and I am looking for some programming wisdom. When faced with a programming challenge, I feel the most important question is "which programming paradigm(s) are better suited to handle it, and how to apply them". A distant second is "which language to use". Yet it seems that most of the programming related content I stumble upon on the Internet has it exactly backwards and focuses mostly on the language choice. An object-oriented solution is fundamentaly the same, whether it's implemented in c++, Java or PHP... So where is the paradigm centered content? Where is the "practical guide to programming paradigms and implementations" and other literature helping bringing real-world and programming concepts together? Note: I already know about "Programming Paradigms for Dummies: What Every Programmer Should Know" from Peter Van Roy.

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• Task queue java

  - by user268515

  Hi i'm new to Task queue concepts when i referred the guide I got struck on this line queue.add( DatastoreServiceFactory.getDatastoreService().getCurrentTransaction(), TaskOptions().url("/path/to/my/worker")); what is TaskOptions() method. Is it default method are method created manually what will TaskOptions() method will return. I created a method called TaskOption() when i to return a string value its saying error as "The method url(String) is undefined for the type String" In url what i want to specify servlet are any other. My doubt may be stupid but plz clarify it. Thank you, sharun.

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• MVC pattern and (Game) State pattern

  - by topright

  Game States separate I/O processing, game logic and rendering into different classes: while (game_loop) { game->state->io_events(this); game->state->logic(this); game->state->rendering(); } You can easily change a game state in this approach. MVC separation works in more complex way: while (game_loop) { game->cotroller->io_events(this); game->model->logic(this); game->view->rendering(); } So changing Game States becomes error prone task (switch 3 classes, not 1). What are practical ways of combining these 2 concepts?

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• MFC Dll with COM Interface

  - by Harsha

  Hi All, I am pretty new to managed/unmanaged interoperability and COM concepts. I received a suggestion of using COM Interop, for using my existing MFC code in C#. But the problem for me is, i have a MFC Dll which is not a valid COM component. How to make this MFC DLLs to have COM-accessible interfaces ready for use in .NET. I tried to search for any settings to make it COM accessible, but was not able to understand any!! Any suggestions or ideas are welcome. Thanks a lot!

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• Forms Authentication and Login controls

  - by DotnetDude

  I am upgrading a website written using ASP.NET 1.1 and the logic for the login page includes verifying the credentials, calling FormsAuthentication.SetAuthCookie() and populating the Session with the user information. I am updating this page to use Login controls and the Membership API and am trying to wrap my head around the concepts that have been changed. Most of the samples I see do not do anything on the login button event handler, so is the logic of setting the cookie abstracted out into the control? Also, how do I check if a user is logged in or not on other pages. Does it still store user information using the Session? How do I check if a user belongs to a particular role or not (Earlier, I would look in the Session object to do something like this) Is the Session a bad way of storing user info? Thanks

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• Suggestions for Single-Page Web Application Design?

  - by DaveDev

  My view is that unless you need to change the basic structure of the user interface, you should not have to reload the page at all for any user interactions. I'd like to approach my next ASP.NET MVC project with this in mind. Can anyone suggest any principles, patterns or practices* I should consider? Excellent book, btw. Still trying to wrap my head around some of the concepts though. I thought a question like this would help link the theory to a practical design. Thanks

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• Memory management, and async operations: when does an object become nil?

  - by Kenny Winker

  I have a view that will be displaying downloaded images and text. I'd like to handle all the downloading asynchronously using ASIHTTPRequest, but I'm not sure how to go about notifying the view when downloads are finished... If I pass my view controller as the delegate of the ASIHTTPRequest, and then my view is destroyed (user navigates away) will it fail gracefully when it tries to message my view controller because the delegate is now nil? i.e. if i do this: UIViewController *myvc = [[UIViewController alloc] init]; request.delegate = myvc; [myvc release]; Do myvc, and request.delegate now == a pointer to nil? This is the problem with being self-taught... I'm kinda fuzzy on some basic concepts. Other ideas of how to handle this are welcome.

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• What trivial real-life example do you use to explain programming to total non-programmers?

  - by anon

  Programmers seem to live in a world of their own (as this site indicates), with their own vibrant culture - and their own premises and vocabulary. Once we've been in the field for a bit, we take a lot of things for granted. But I'm often faced with the question "What do you do?" Or "What is programming?" I generally try to answer this with a small, often trivial, real-world example of how programming is prevalent in our everyday lives and keeps things running. The example I use most often is an elevator - someone has to program the logic of that... And I've seen elevators that are "smart" and ones that are quite backwards and foolish. (And you can easily understand if/decision and looping from that... incorporates a lot of important programming concepts in a very small example.) I've sometimes heard people use traffic lights as an example. What example do you / would you use to explain the concept of programming to someone completely clueless?

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• Python questions from beginner

  - by ChrisC

  I'm thinking about rewriting an MS Access db I wrote years ago into a stand-alone Python app. Other than a college class called "Intro to C++" (console only, with OOP concepts) and the Access db itself, I have no experience, so I need to ask if the basis for my decision to go with Python is correct. Is it true that: 1) Python is relatively easy to pick up? 2) Python apps can run as "portable" (ie from one directory, no registry needs, nothing needs to be pre-installed on a Windows PC) as long as I use an embedded db?

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• Teach Perl as a first language?

  - by yossale

  I need to teach a non-programmer the basics of computer programming + some basic programming skills (- He's going to be in a position between the clients and the programmers , so the company requires him to learn the basic concepts of programming). I thought of Perl - You can teach it without getting into typing and pointers and it's syntax is very close to human (precious "bless" :) ) - but I'm a bit troubled because I feel like I'm going to "spoil" him for other languages in the future (C,C++,Java - What some people call "Real" languages) - exactly because of the reasons mentioned above. What do you think?

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• ASP.NET or ASP.NET MVC or Silverlight or a mixture of all ?

  - by Elmex

  I want to start to implement a new web application from the scratch. I have 2 years experiences with ASP.NET. Now Microsoft offers ASP.NET MVC. I have read a little about the concepts behind, but I am not sure if I should use the classic ASP.NET variant or the new one. Perhaps it makes sense to mix it ? Or should I move to Silverlight ? What do you thing ? What are the advantages and disadvantages of all these variants ?

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• Idiomatic ruby for temporary variables within a method

  - by Andrew Grimm

  Within a method, I am using i and j as temporary variables while calculating other variables. What is an idiomatic way of getting rid of i and j once they are no longer needed? Should I use blocks for this purpose? i = positions.first while nucleotide_at_position(i-1) == nucleotide_at_position(i) raise "Assumption violated" if i == 1 i -= 1 end first_nucleotide_position = i j = positions.last while nucleotide_at_position(j+1) == nucleotide_at_position(j) raise "Assumption violated" if j == sequence.length j += 1 end last_nucleotide_position = j Background: I'd like to get rid of i and j once they are no longer needed so that they aren't used by any other code in the method. Gives my code less opportunity to be wrong. I don't know the name of the concept - is it "encapsulation"? The closest concepts I can think of are (warning: links to TV Tropes - do not visit while working) Chekhov'sGun or YouHaveOutlivedYourUsefulness. Another alternative would be to put the code into their own methods, but that may detract from readability.

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