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• Learning how to design knowledge and data flow [closed]

  - by max

  In designing software, I spend a lot of time deciding how the knowledge (algorithms / business logic) and data should be allocated between different entities; that is, which object should know what. I am asking for advice about books, articles, presentations, classes, or other resources that would help me learn how to do it better. I code primarily in Python, but my question is not really language-specific; even if some of the insights I learn don't work in Python, that's fine. I'll give a couple examples to clarify what I mean. Example 1 I want to perform some computation. As a user, I will need to provide parameters to do the computation. I can have all those parameters sent to the "main" object, which then uses them to create other objects as needed. Or I can create one "main" object, as well as several additional objects; the additional objects would then be sent to the "main" object as parameters. What factors should I consider to make this choice? Example 2 Let's say I have a few objects of type A that can perform a certain computation. The main computation often involves using an object of type B that performs some interim computation. I can either "teach" A instances what exact parameters to pass to B instances (i.e., make B "dumb"); or I can "teach" B instances to figure out what needs to be done when looking at an A instance (i.e., make B "smart"). What should I think about when I'm making this choice?

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• Why is this beat detection code failing to register some beats properly?

  - by Quincy

  I made this SoundAnalyzer class to detect beats in songs: class SoundAnalyzer { public SoundBuffer soundData; public Sound sound; public List<double> beatMarkers = new List<double>(); public SoundAnalyzer(string path) { soundData = new SoundBuffer(path); sound = new Sound(soundData); } // C = threshold, N = size of history buffer / 1024 B = bands public void PlaceBeatMarkers(float C, int N, int B) { List<double>[] instantEnergyList = new List<double>[B]; GetEnergyList(B, ref instantEnergyList); for (int i = 0; i < B; i++) { PlaceMarkers(instantEnergyList[i], N, C); } beatMarkers.Sort(); } private short[] getRange(int begin, int end, short[] array) { short[] result = new short[end - begin]; for (int i = 0; i < end - begin; i++) { result[i] = array[begin + i]; } return result; } // get a array of with a list of energy for each band private void GetEnergyList(int B, ref List<double>[] instantEnergyList) { for (int i = 0; i < B; i++) { instantEnergyList[i] = new List<double>(); } short[] samples = soundData.Samples; float timePerSample = 1 / (float)soundData.SampleRate; int sampleIndex = 0; int nextSamples = 1024; int samplesPerBand = nextSamples / B; // for the whole song while (sampleIndex + nextSamples < samples.Length) { complex[] FFT = FastFourier.Calculate(getRange(sampleIndex, nextSamples + sampleIndex, samples)); // foreach band for (int i = 0; i < B; i++) { double energy = 0; for (int j = 0; j < samplesPerBand; j++) energy += FFT[i * samplesPerBand + j].GetMagnitude(); energy /= samplesPerBand; instantEnergyList[i].Add(energy); } if (sampleIndex + nextSamples >= samples.Length) nextSamples = samples.Length - sampleIndex - 1; sampleIndex += nextSamples; samplesPerBand = nextSamples / B; } } // place the actual markers private void PlaceMarkers(List<double> instantEnergyList, int N, float C) { double timePerSample = 1 / (double)soundData.SampleRate; int index = N; int numInBuffer = index; double historyBuffer = 0; //Fill the history buffer with n * instant energy for (int i = 0; i < index; i++) { historyBuffer += instantEnergyList[i]; } // If instantEnergy / samples in buffer < instantEnergy for the next sample then add beatmarker. while (index + 1 < instantEnergyList.Count) { if(instantEnergyList[index + 1] > (historyBuffer / numInBuffer) * C) beatMarkers.Add((index + 1) * 1024 * timePerSample); historyBuffer -= instantEnergyList[index - numInBuffer]; historyBuffer += instantEnergyList[index + 1]; index++; } } } For some reason it's only detecting beats from 637 sec to around 641 sec, and I have no idea why. I know the beats are being inserted from multiple bands since I am finding duplicates, and it seems that it's assigning a beat to each instant energy value in between those values. It's modeled after this: http://www.flipcode.com/misc/BeatDetectionAlgorithms.pdf So why won't the beats register properly?

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• libgtk2.0-common fails to build with Gdk-2.0.gir error, Type reference 'GdkPixbuf' not found

  - by Stefano Palazzo

  I'm trying to build gtk, but it fails. Here's what I'm doing: sudo apt-get build-dep libgtk2.0-common sudo apt-get source libgtk2.0-common cd gtk+2.0-2.22.0/ sudo gedit gtk/gtktreeview.c & #...editing a few files (or not, it's the same error) sudo ./configure --prefix=/usr sudo make The compilation runs for a while and then quits: Gdk-2.0.gir: error: Type reference 'GdkPixbuf' not found ... make: *** [all] Error 2 What am I doing wrong?

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• Is return-type-(only)-polymorphism in Haskell a good thing?

  - by dainichi

  One thing that I've never quite come to terms with in Haskell is how you can have polymorphic constants and functions whose return type cannot be determined by their input type, like class Foo a where foo::Int -> a Some of the reasons that I do not like this: Referential transparency: "In Haskell, given the same input, a function will always return the same output", but is that really true? read "3" return 3 when used in an Int context, but throws an error when used in a, say, (Int,Int) context. Yes, you can argue that read is also taking a type parameter, but the implicitness of the type parameter makes it lose some of its beauty in my opinion. Monomorphism restriction: One of the most annoying things about Haskell. Correct me if I'm wrong, but the whole reason for the MR is that computation that looks shared might not be because the type parameter is implicit. Type defaulting: Again one of the most annoying things about Haskell. Happens e.g. if you pass the result of functions polymorphic in their output to functions polymorphic in their input. Again, correct me if I'm wrong, but this would not be necessary without functions whose return type cannot be determined by their input type (and polymorphic constants). So my question is (running the risk of being stamped as a "discussion quesion"): Would it be possible to create a Haskell-like language where the type checker disallows these kinds of definitions? If so, what would be the benefits/disadvantages of that restriction? I can see some immediate problems: If, say, 2 only had the type Integer, 2/3 wouldn't type check anymore with the current definition of /. But in this case, I think type classes with functional dependencies could come to the rescue (yes, I know that this is an extension). Furthermore, I think it is a lot more intuitive to have functions that can take different input types, than to have functions that are restricted in their input types, but we just pass polymorphic values to them. The typing of values like [] and Nothing seems to me like a tougher nut to crack. I haven't thought of a good way to handle them. I doubt I am the first person to have had thoughts like these. Does anybody have links to good discussions about this Haskell design decision and the pros/cons of it?

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• What makes C so popular in the age of OOP?

  - by GradGuy

  I code a lot both in C and C++ but did not expect C to be the second popular language, slightly behind Java! http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html I'm curious as why, in this age of OOP, C is still all that popular? Note that 4 out of top 5 popular languages are all "modern" object-oriented capable languages. Now I agree that you can do OOP in C to some extend, but that's sort of painful and not quite elegant! (well at least compared to C++ I guess) So what makes C this popular? efficiency? being low-level? or the vast majority of libraries that already exist? ... or something else?

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• How do I add restrictions for users to sign up before they can access web site?

  - by user1867842

  How do I get my webpage not to go back when they hit the back button and are logged out and how can I add a web page to be blocked like FACEBOOK doesn't let you get into their site with out having a page or a account with them, and if you try to put something in the url and try to go to something on their site it gives you a web page that says "you have to be logged in first" . Like I don't want someone going to the url of the "index" page before they have signed up as a member they need to make an account first then they can have access to the "index" page. How do I do this. I have a website so far that has a database and the website has 5 pages so far and two of them which is the login and sign up page which are both used with php and mysql and they work fine. How do I restrict access to the main website by first having the users sign up with me for an account.

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• How would I go about implementing a globe-like "ballish" map?

  - by rFactor

  I am new to 3D development and I have this idea of having the game world like our globe is - a ball. So, there would be no corners in the map and the game is top-down RTS game. I would like the camera to go on and on and never stop even though you are moving the camera to the same direction all the time. I am not sure if this is even possible, but I would really like to build a globe-like map without borders. Can this be done, and how exactly? I am using XNA, C#, and DirectX. Any tutorials or links or help is greatly appreciated!

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• What are the caveats of the event system built on Messenger rather than on classic .NET events?

  - by voroninp

  MVVM Light and PRISM offer messenger to implement event system. the approximate interface looks like the following one: interface Messanger { void Subscribe<TMessageParam>(Action<TMessageParam> action); void Unsubscribe<TMessageParam>(Action<TMessageParam> action); void Unsubscribe<TMessageParam>(objec actionOwner); void Notify<TMessageParam>(TMessageParam param); } Now this model seems beneficial comparing to classic .net events. It works well with Dependency Injection. Actions are stored as weak references so memory leaks are avioded and unsubscribe is not a must. The only annoyance is the need to declare new TMessageParam for each specific message. But everything comes at a cost. And what I'm really worried about is that I see no shortcomings of this approach. Has anoyne the experience of some troubles with this design pattern?

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• SQL Server Unit Testing with tSQLt

  When one considers the amount of time and effort that Unit Testing consumes for the Database Developer, is surprising how few good SQL Server Test frameworks are around. tSQLt , which is open source and free to use, is one of the frameworks that provide a simple way to populate a table with test data as part of the unit test, and check the results with what should be expected. Sebastian and Dennis, who created tSQLt, explain.

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• Expected time for lazy evaluation with nested functions?

  - by Matt_JD

  A colleague and I are doing a free R course, although I believe this is a more general lazy evaluation issue, and have found a scenario that we have discussed briefly and I'd like to find out the answer from a wider community. The scenario is as follows (pseudo code): wrapper => function(thing) { print => function() { write(thing) } } v = createThing(1, 2, 3) w = wrapper(v) v = createThing(4, 5, 6) w.print() // Will print 4, 5, 6 thing. v = create(7, 8, 9) w.print() // Will print 4, 5, 6 because "thing" has now been evaluated. Another similar situation is as follows: // Using the same function as above v = createThing(1, 2, 3) v = wrapper(v) w.print() // The wrapper function incestuously includes itself. Now I understand why this happens but where my colleague and I differ is on what should happen. My colleague's view is that this is a bug and the evaluation of the passed in argument should be forced at the point it is passed in so that the returned "w" function is fixed. My view is that I would prefer his option myself, but that I realise that the situation we are encountering is down to lazy evaluation and this is just how it works and is more a quirk than a bug. I am not actually sure of what would be expected, hence the reason I am asking this question. I think that function comments could express what will happen, or leave it to be very lazy, and if the coder using the function wants the argument evaluated then they can force it before passing it in. So, when working with lazy evaulation, what is the practice for the time to evaluate an argument passed, and stored, inside a function?

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• How to avoid the GameManager god object?

  - by lorancou

  I just read an answer to a question about structuring game code. It made me wonder about the ubiquitous GameManager class, and how it often becomes an issue in a production environment. Let me describe this. First, there's prototyping. Nobody cares about writing great code, we just try to get something running to see if the gameplay adds up. Then there's a greenlight, and in an effort to clean things up, somebody writes a GameManager. Probably to hold a bunch of GameStates, maybe to store a few GameObjects, nothing big, really. A cute, little, manager. In the peaceful realm of pre-production, the game is shaping up nicely. Coders have proper nights of sleep and plenty of ideas to architecture the thing with Great Design Patterns. Then production starts and soon, of course, there is crunch time. Balanced diet is long gone, the bug tracker is cracking with issues, people are stressed and the game has to be released yesterday. At that point, usually, the GameManager is a real big mess (to stay polite). The reason for that is simple. After all, when writing a game, well... all the source code is actually here to manage the game. It's easy to just add this little extra feature or bugfix in the GameManager, where everything else is already stored anyway. When time becomes an issue, no way to write a separate class, or to split this giant manager into sub-managers. Of course this is a classical anti-pattern: the god object. It's a bad thing, a pain to merge, a pain to maintain, a pain to understand, a pain to transform. What would you suggest to prevent this from happening?

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• What's the reason exceptions are heavily used in managed (C# and Java) languages but not in C++? [on hold]

  - by ZijingWu

  AFAIK, a lot of C++ projects don't allow exceptions and deny them in coding guidelines. I have a lot of reasons, for example, exception is hard to handle correctly if your binary needs to be compiled by separate and different compilers. But it doesn't fully convince me, there is a lot of projects which are just using one compiler. Compared to C++, exceptions are heavily used in C# and Java and the reason can only be that exception are not bringing enough benefit. One point is debugbility in practice. Exception can not get the call stack in C++ code, but in C# and Java you can get the call stack from exception, it is significant and makes debugging easier. No-callstack is not the fault of the exception, it is the language difference, but it impacts the exception usage. So what's the reason that exceptions are frowned upon in c++ programs?

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• Do first-class methods exist?

  - by gdhoward

  Okay, I know first-class functions are cool, closures even better, etc. But is there any language with first-class methods? In my mind, I see a first-class method as an "object" that has both a function pointer and a pointer to a specific instance of the class/object, but the implementation doesn't matter. I just want to know if there is any language that uses them. And as a bonus, how were they implemented?

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• I can't see how a mature agile team requires any *management*?

  - by ashy_32bit

  After a recent heated debate over Scrum, I realized my problem is that I think of management as a quite unnecessary and redundant activity in a fully agile team. I believe a mature Agile team does not require management or any non-technical decision making process of whatsoever. To my (apparently erring) eyes it is more than obvious that the only one suitable and capable of managing a mature development team is their coach (and that being the most technically competent colleague with proper communication skills). I can't imagine how a Scrum master can contribute to such a team. I am having a great difficulty realizing and understanding the value of such things as Scrum and manager as someone who is not a veteran developer but is well skilled in planning the production cycles when a coach exists in the team. What does that even mean? How on earth someone with no edge-skills of development can manage a highly technical team? Perhaps management here means something else? I see management as a total waste of time and a by-product of immaturity. In my understanding a mature team is fully self-managing. Apparently I'm mistaken since many great people say the contrary but I can't convince myself.

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• I just received a complaint from a user of the website I maintain. Should I do anything?

  - by Chris

  I was sent sent a large wall of text from a user of the website I maintain at my job. They are clearly upset for having to deal with a horribly outdated web application that has not seen any serious updates in over 6+ years. No refactoring has been done, the code quality is terrible, the security unchecked, policy compliances ignored, in addition to being ugly and frankly embarrassing. Keep in mind this is a small business but the website is used by hundreds daily. I'm one of two programmers there, and I've been working there for two years. This person says they are about my age (22) and understand technology (but can't use proper grammar). The complaint mentioned awkward pages and actions on the website, but they don't even have a clue as to the depth of the flaws in this website. Now, I would love to honestly tell them that there's a lot wrong with this company and that this application was built when we were in high school. And that while it's not my fault that the website is terrible, I'm the one in position to fix it. But on the other hand, I could just say nothing and ignore it. Would doing this publicly have any advantage to future employees (showing integrity) or would it just be a completely pointless mistake? Odds are, even if I respond only that one person will ever read it. Regardless, I'm probably just going to ignore it and continue starting my project to refactor the website.

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• What Shading/Rendering techniques are being used in this image?

  - by Rhakiras

  My previous question wasn't clear enough. From a rendering point of view what kind of techniques are used in this image as I would like to apply a similar style (I'm using OpenGL if that matters): http://alexcpeterson.com/ My specific questions are: How is that sun glare made? How does the planet look "cartoon" like? How does the space around the planet look warped/misted? How does the water look that good? I'm a beginner so any information/keywords on each question would be helpful so I can go off and learn more. Thanks

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• Could I be going crazy with Event Handlers? Am I going the "wrong way" with my design?

  - by sensae

  I guess I've decided that I really like event handlers. I may be suffering a bit from analysis paralysis, but I'm concerned about making my design unwieldy or running into some other unforeseen consequence to my design decisions. My game engine currently does basic sprite-based rendering with a panning overhead camera. My design looks a bit like this: SceneHandler Contains a list of classes that implement the SceneListener interface (currently only Sprites). Calls render() once per tick, and sends onCameraUpdate(); messages to SceneListeners. InputHandler Polls the input once per tick, and sends a simple "onKeyPressed" message to InputListeners. I have a Camera InputListener which holds a SceneHandler instance and triggers updateCamera(); events based on what the input is. AgentHandler Calls default actions on any Agents (AI) once per tick, and will check a stack for any new events that are registered, dispatching them to specific Agents as needed. So I have basic sprite objects that can move around a scene and use rudimentary steering behaviors to travel. I've gotten onto collision detection, and this is where I'm not sure the direction my design is going is good. Is it a good practice to have many, small event handlers? I imagine going the way I am that I'd have to implement some kind of CollisionHandler. Would I be better off with a more consolidated EntityHandler which handles AI, collision updates, and other entity interactions in one class? Or will I be fine just implementing many different event handling subsystems which pass messages to each other based on what kind of event it is? Should I write an EntityHandler which is simply responsible for coordinating all these sub event handlers? I realize in some cases, such as my InputHandler and SceneHandler, those are very specific types of events. A large portion of my game code won't care about input, and a large portion won't care about updates that happen purely in the rendering of the scene. Thus I feel my isolation of those systems is justified. However, I'm asking this question specifically approaching game logic type events.

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• Advice on what to learn? [closed]

  - by ICTech

  Currently I work as a .NET C# programmer, quite fresh faced at that (only been working professionally for 8 months) I'm enjoying what I'm doing, but I'm now thinking ahead for other languages to learn. I've heard from quite a few seasoned developers that they reckon it's worth getting in to HTML5. Before I asked this question I read a few of the other questions similar to this, but most were dated back a few years. I'm wondering what your advice would be to an aspiring programmer, what I should avoid going for (i.e. as I understand it Flash is essentially going to be phased out due to HTML5) I was looking in to WPF and the more updated .NET technologies, but someone advised me that WPF stuff will probably be redundant in the future. Thanks for your advice and opinions :)

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• How to avoid whitespace in PHP and ASP.NET? [closed]

  - by Goma

  You know that the PHP interpreter avoids whitespace and comments. However, I have heared that there is something you can do to make the interpreter does not see the whitespace at all and does not even think to avoid it, the same for the compiler in ASP.NET. What is that thing? Is it a function in PHP and a class in ASP.NET? or what exactly? Edit: For example the php_strip_whitespace function in PHP "Returns the PHP source code in filename with PHP comments and whitespace removed". Will this help in load time?

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• Isn't Java a quite good choice for desktop applications?

  - by tactoth

  At present most applications are still developed with C++, painfully. Lack of portability, in compatible libraries, memory leaks, slow compilation, and poor productivity. Even if you pick only a single from these shortages, it's still a big headache. However the surprising truth is that C++ remains the first choice for desktop applications. Compared to C++ Java has lots of advantages. The success in server side development shows that the language itself is good, Swing is also thought to be as programmer friendly as the highly recognized QT framework (No, never say even a single word about MFC!). All the disadvantages of C++ listed above has a solution in Java. "Performance!", Well that might still be the problem but to my experience it's a slight problem. I'd been using Java to decode some screen video and generate key frames. The video has a duration of more than 1 hour. The time spent on an average machine is just 1 minute. With C++ I don't expect even faster speed. In recent days there are many news on the JIT performance improvements, that make us feel Java is gradually becoming very suitable for desktop development, without people realizing it. Isn't it?

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• Fewer SQL Developers needed?

  - by Mercfh

  According to Tiobe, http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html (not exactly reliable but still) and just noticing around here. I see less talk about SQL in general? Has there been a slump in web development that uses databases like Mysql, or Data Warehousing here recently? Or have alternate solutions like NoSQL/CouchDB/MongoDB started to take over or what? or have I just been missing something?

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• Rhythmbox plugin code for hot key not working - why?

  - by Bunny Rabbit

  def activate(self,shell): self.shell = shell self.copy_selected() self.action = gtk.Action ('foo','bar','baz',None) self.activate_id = self.action.connect ('activate', self.call_bk_fn,self.shell) self.action_group = gtk.ActionGroup ('hot_key_action_group') self.action_group.add_action_with_accel (self.action, "<control>E") uim = shell.get_ui_manager () uim.insert_action_group (self.action_group, 0) uim.ensure_update () def call_bk_fn(): print('hello world') I am using the above code in a plugin for Rhythmbox and here I am trying to register the key Ctrl+E so that the call_bk_fn gets called whenever the key combination is pressed but its not working. Why is that so ?

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• Collaborative Filtering Techniques

  - by user95261

  Good Day! I am in need of help about collaborative filtering techniques implementation in predicting psychopathy of twitter users. I have two data set, training set and test set. Training set users have already scores in psychopathy, I need any collaborative filtering techniques to predict scores of test set users. Collaborative Filtering such as Item/User-Based CF, Bayesian Belief Nets, Clustering, Latent Semantic, etc. Please help me. :( I am very confused on how to implement any of these. Thank you!

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• What's involved in resetting the graphics device?

  - by Donutz

  I'm playing with XNA 4.0, VS2010. I've created a window (not maximized) and drawn some sprites. All is good until I resize the window, after which the sprites stop displaying or only partially display. I'm pretty sure it has something to do with needing to reset the device or something, but can't find any clear instructions or sample code. It's not just a case of needing to increase the preferredbackbuffer size, because even if I shrink the window I get this symptom. I've looked at the source code that I was able to get from Microsoft before they shut down XNA, but it doesn't actually explain anything. Any help or advice? If it makes any difference I'm creating DrawableGameComponents and doing my updates and drawing in their Draw/Update routines.

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• reading k&r(c book) and confusing 1st chapter code [closed]

  - by DarkEnergy

  #include <stdio.h> /* copy input to output; 2nd version*/ main() { int c; while ((c = getchar()) != EOF) putchar(c); } this is very confusing... since you never escape the while loop. I've learned that EOF is -1. i type -1 but it just reprints it. It's a never ending loop. Over time did the library get changed and differs from what the book intended it to be? when i say library i mean the putchar()/getchar() that's in the library... sorry.

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