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• Problem drawing a polygon on data clusters in MATLAB

  - by Hossein

  Hi, I have some data points which I have devided into them into some clusters with some clustering algorithms as the picture below:(it might takes some time for the image to appear) Each color represents different cluster. I have to draw polygons around each cluster. I use convhull for this reason. But as you can see the polygon for the red cluster is very big and covers a lot of areas, which is not the one I am looking for. I need to draw lines(ploygons) exactly around my data sets. For example in the picture above I want a polygon that is drawn exactly the same(and around) as the red cluster with the 3 branches. In other words, in this case I need a polygon with 3 branches to cover my red clusters not that big polygon that covers the whole area. Can anyone help me with this? Please Note that the solution should be general, because the clusters will change in each run of the algorithm, so it needs to be in a way that is general.

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• I like to learn computer science and programming, but i have no understanding.

  - by Josiah

  Hi all, I like to learn computer science and programming, but i don't know where and how to start. For the past two months, i have been researching on types of programming, i found my interest in desktop programming, and also found this subjects (discrete maths, logic, algorithms, data structures, artificial intelligence, simulation) said to be a most known (subjects). Well as a beginner, i have no understanding on what type of language or books that can cover all these subjects, or even how to write any code. Secondly, am as young as you can guess and i need a language to start with that will be easy for me to understand, and books to read. Thank you.

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• Are all the system's floating points operations the same?

  - by Jj

  We're making this web app in PHP and when working in the reports we have Excel files to compare our results to make sure our coding is doing the right operations. Now we're running into some differences due floating point arithmetics. We're doing the same divisions and multiplications and running into slightly different numbers, that add up to a notable difference. My question is if Excel is delegating it's floating point arithmetic to the CPU and PHP is also relying in the CPU for it's operations. Or does each application implements its own set of math algorithms?

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• Load balancer - how to write one for a custom application?

  - by Poni

  Hi! I've written a simple server application which will run distributed on several machines. My question is how does a network load balancer works, in general? I've heard of round-robin and other algorithms, but what I haven't got answer to is how does the process really goes? In socket terms. The client connects to one of the load balancer machines, asks for a "free-to-connect-to" server and simply connects to it? That's the simpliest way I can think of. .. or, does it use the load balancer as a proxy (that implies that all the NBs must be always connected to the application servers, and data is transferred through them)? It's more of a general question. How would you do this? Thank you all!

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• Which build tool to teach?

  - by Helper Method

  While similiar questions have been asked, this one's focused on which is best/easiest to teach. I'm giving a weekly tutorial at my university focusing on data structures and algorithms. Fromn time to time I introduce tools which may prove helpful in future projects like JUnit, Mercurial, Eclipse etc.. I plan to show them some kind of build tool but I'm not sure which one to choose. I by myself have very little knowledge about build tools, except a little experience in using make. It's more the concept of a build tool I want to show them, not a special tool per se. Which would be the most easiest/future proof/whatever tool to show them? I've read a little bit about Gradle, which looks nice, but so far I think Ant could be a good choice (it's a Java course I'm giving).

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• Java: Best practices for turning foreign horror-code into clean API...?

  - by java.is.for.desktop

  Hello, everyone! I have a project (related to graph algorithms). It is written by someone else. The code is horrible: public fields, no getters/setters huge methods, all public some classes have over 20 fields some classes have over 5 constructors (which are also huge) some of those constructors just left many fields null (so I can't make some fields final, because then every second constructor signals errors) methods and classes rely on each other in both directions I have to rewrite this into a clean and understandable API. Problem is: I myself don't understand anything in this code. Please give me hints on analyzing and understanding such code. I was thinking, perhaps, there are tools which perform static code analysis and give me call graphs and things like this.

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• Fastest way of converting a quad to a triangle strip?

  - by Tina Brooks

  What is the fastest way of converting a quadrilateral (made up of foyr x,y points) to a triangle strip? I'm well aware of the general triangulation algorithms that exist, but I need a short, well optimized algorithm that deals with quadrilaterals only. My current algorithm does this, which works for most quads but still gets the points mixed up for some: #define fp(f) bounds.p##f /* Sort four points in ascending order by their Y values */ point_sort4_y(&fp(1), &fp(2), &fp(3), &fp(4)); /* Bottom two */ if (fminf(-fp(1).x, -fp(2).x) == -fp(2).x) { out_quad.p1 = fp(2); out_quad.p2 = fp(1); } else { out_quad.p1 = fp(1); out_quad.p2 = fp(2); } /* Top two */ if (fminf(-fp(3).x, -fp(4).x) == -fp(3).x) { out_quad.p3 = fp(3); out_quad.p4 = fp(4); } else { out_quad.p3 = fp(4); out_quad.p4 = fp(3); }

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• best method of turning millions of x,y,z positions of particles into visualisation

  - by Griff

  I'm interested in different algorithms people use to visualise millions of particles in a box. I know you can use Cloud-In-Cell, adaptive mesh, Kernel smoothing, nearest grid point methods etc to reduce the load in memory but there is very little documentation on how to do these things online. i.e. I have array with: x,y,z 1,2,3 4,5,6 6,7,8 xi,yi,zi for i = 100 million for example. I don't want a package like Mayavi/Paraview to do it, I want to code this myself then load the decomposed matrix into Mayavi (rather than on-the-fly rendering) My poor 8Gb Macbook explodes if I try and use the particle positions. Any tutorials would be appreciated.

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• Using EXR images in OpenCV

  - by Nestor

  Hi there! I'm currently working on a project with OpenEXR and I would like to implement some Blob detection algorithms. To do this I figured that I could use OpenCV as it says in the documentation that it can open OpenEXR format files. I have all the libraries installed and working as I've been doing other things. I open a simple jpg file with openCV cvLoadImage. It works fine. But when i try to open any .exr file it doesn't seam to like it. I get a gray window where there should be the image display. Has anyone done any tests with OpenCV and OpenEXR libraries working together? Have they worked for you? What do you think? Thanks.

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• I need to stop execution during recursive algorithm

  - by Shaza

  Hey, I have a problem in choosing the right method to accomplish my goal. I'm working on Algorithms teaching system, I'm using C#. I need to divide my algorithm into steps, each step will contain a recursion. I have to stop execution after each step, user can then move to the next step(next recursion) using a button in my GUI. After searching, threads was the right choice, but I found several methods: (Thread.sleep/interrupt): didn't work, my GUI freezed !! (Suspend/Resume): I've read that it's a bad idea to use. (Waithandles): still reading about them. (Monitor wait/resume). I don't have much time to try and read all previous methods, please help me in choosing the best method that fits my system.Any suggestions are extremal welcomed.

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• Program to call other programs

  - by Evil

  hello. I am writing a program that will solve a type of min. spanning tree problem. i have 2 different algorithms that I've gotten working in two separate .cpp files i've named kruskels.cpp and prims.cpp. my question is this: each file takes the following command line to run it . time ./FILENAME INPUTFILE FACTOR i would like to make a program that, depending on what inputfile is entered, will run either kruskels.cpp or prims.cpp. how can i do this? this program must pass those command line arguments to kruskels or prims. each file (kruskels.cpp and prims.cpp) are designed to be run using those command line arugments (so they take in INPUTFILE and FACTOR as variables to do file io). this should be for c++.

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• st-ordering library function?

  - by chang

  I'm in the search for an implementation of an ear-decomposition algorithm (http://www.ics.uci.edu/~eppstein/junkyard/euler/ear.html). I examined networkx and didn't find one. Although the algorithm layout is vaguely in my mind, I'd like to see some reference implementation, too. Side problem: First step could be an st-ordering of a graph. Are there any implementations for st-ordering algorithms you know? Thanks for your input. I'd really like to contribute e.g. to networkx by implementing the ear-decomposition algorithm in python.

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• Is there a sample set of web log data available for testing analysis against?

  - by Peter

  Sorry if this isn't strictly speaking a programming question, but I figure my best chance of success would be to ask here. I'm developing some web log file analysis algorithms, but to date I only have access to a fairly small amount of web log data to process. One algorithm I want to use makes some assumptions about 'the shape' of typical web log data, and so I'd like to test it against a larger 'exemplar' - perhaps the logs of a busy site with a good distribution of traffic from different sources etc. Is there a set of such data available somewhere? Thanks for any help.

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• What are some C++ Standard Library usage best practices?

  - by apphacker

  I'm learning C++ and the book I'm reading (The C++ Programming Language) says to not reinvent the wheel, to rely on the standard libraries. In C, I often end up creating a linked list, and link list iteration over and over again (maybe I'm doing that wrong not sure), so the ideas of containers available in C++, and strings, and algorithms really appeal to me. However I have read a little online, and heard some criticisms from my friends and coworkers about STL, so I thought I maybe I'd pick some brains here. What are some best practices for using STL, and what lessons have you learned about STL?

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• What is the best Java numerical method package?

  - by Bob Cross

  I am looking for a Java-based numerical method package that provides functionality including: Solving systems of equations using different numerical analysis algorithms. Matrix methods (e.g., inversion). Spline approximations. Probability distributions and statistical methods. In this case, "best" is defined as a package with a mature and usable API, solid performance and numerical accuracy. Edit: derick van brought up a good point in that cost is a factor. I am heavily biased in favor of free packages but others may have a different emphasis.

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• Algorithm to match natural text in mail

  - by snøreven

  I need to separate natural, coherent text/sentences in emails from lists, signatures, greetings and so on before further processing. example: Hi tom, last monday we did bla bla, lore Lorem ipsum dolor sit amet, consectetur adipisici elit, sed eiusmod tempor incidunt ut labore et dolore magna aliqua. list item 2 list item 3 list item 3 Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid x ea commodi consequat. Quis aute iure reprehenderit in voluptate velit regards, K. ---line-of-funny-characters-####### example inc. 33 evil street, london mobile: 00 234534/234345 Ideally the algorithm would match only the bold parts. Is there any recommended approach - or are there even existing algorithms for that problem? Should I try approximate regular expressions or more statistical stuff based on number of punctation marks, length and so on?

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• Can 3D OpenGL game written in Python look good and run fast?

  - by praavDa

  I am planning to write an simple 3d(isometric view) game in Java using jMonkeyEngine - nothing to fancy, I just want to learn something about OpenGL and writing efficient algorithms (random map generating ones). When I was planning what to do, I started wondering about switching to Python. I know that Python didn't come into existence to be a tool to write 3d games, but is it possible to write good looking games with this language? I have in mind 3d graphics, nice effects and free CPU time to power to rest of game engine? I had seen good looking java games - and too be honest, I was rather shocked when I saw level of detail achieved in Runescape HD. On the other hand, pygame.org has only 2d games, with some starting 3d projects. Are there any efficient 3d game engines for python? Is pyopengl the only alternative? Good looking games in python aren't popular or possible to achieve? I would be grateful for any information / feedback.

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• What is the typical method to separate connected letters in a word using OCR

  - by Maysam

  I am very new to OCR and almost know nothing about the algorithms used to recognize words. I am just getting familiar to that. Could anybody please advise on the typical method used to recognize and separate individual characters in connected form (I mean in a word where all letters are linked together)? Forget about handwriting, supposing the letters are connected together using a known font, what is the best method to determine each individual character in a word? When characters are written separately there is no problem, but when they are joined together, we should know where every single character starts and ends in order to go to the next step and match them individually with a letter. Is there any known algorithm for that?

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• Most efficient algorithm for mesh-level, optimal occlusion culling?

  - by Fredriku73

  I am new to culling. On a first glance, it seems that most occlusion culling algorithms are object-level, not examining single meshes, which would be practical for game rendering. What I am looking for is an algorithm that culls all meshes within a single object that are occluded for a given viewpoint, with high accuracy. It needs to be at least O(n log n), a naive mesh-by-mesh comparison (O(n^2)) is too slow. I notice that the Blender GUI identifies the occluded meshes for you in real-time, even if you work with large objects of 10,000+ meshes. What algorithm is used there, pray tell?

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• Placement of defensive structures in a game

  - by Martin

  I am working on an AI bot for the game Defcon. The game has cities, with varying populations, and defensive structures with limited range. I'm trying to work out a good algorithm for placing defence towers. Cities with higher populations are more important to defend Losing a defence tower is a blow, so towers should be placed reasonably close together Towers and cities can only be placed on land So, with these three rules, we see that the best kind of placement is towers being placed in a ring around the largest population areas (although I don't want an algorithm just to blindly place a ring around the highest area of population, sometime there might be 2 sets of cities far apart, in which case the algorithm should make 2 circles, each one half my total towers). I'm wondering what kind of algorithms might be used for determining placement of towers?

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• Algorithm for non-contiguous netmask match

  - by Gianluca

  Hi, I have to write a really really fast algorithm to match an IP address to a list of groups, where each group is defined using a notation like 192.168.0.0/252.255.0.255. As you can see, the bitmask can contain zeros even in the middle, so the traditional "longest prefix match" algorithms won't work. If an IP matches two groups, it will be assigned to the group containing most 1's in the netmask. I'm not working with many entries (let's say < 1000) and I don't want to use a data structure requiring a large memory footprint (let's say 1-2 MB), but it really has to be fast (of course I can't afford a linear search). Do you have any suggestion? Thanks guys. UPDATE: I found something quite interesting at http://www.cse.usf.edu/~ligatti/papers/grouper-conf.pdf, but it's still too memory-hungry for my utopic use case

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• bluetooth emulators/simulators

  - by scatman

  what are the best bluetooth emulators/simulators? i have a project for the security course, and i chose bluetooth as my topic. so i need to create encryption algorithms using a bluetooth simulator and test them. i have already searched for the best emulaters, and the results were google anroid, and NS2. is there any emulator better? the languages i prefer to program with are c , c++ , and c# java is also not a problem but i prefer any of the above languages.

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• Is there a name for the technique of using base-2 numbers to encode a list of unique options?

  - by Lunatik

  Apologies for the rather vague nature of this question, I've never been taught programming and Google is rather useless to a self-help guy like me in this case as the key words are pretty ambiguous. I am writing a couple of functions that encode and decode a list of options into a Long so they can easily be passed around the application, you know this kind of thing: 1 - Apple 2 - Orange 4 - Banana 8 - Plum etc. In this case the number 11 would represent Apple, Orange & Plum. I've got it working but I see this used all the time so assume there is a common name for the technique, and no doubt all sorts of best practice and clever algorithms that are at the moment just out of my reach.

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• implementing type inference

  - by deepblue

  well I see some interesting discussions here about static vs. dynamic typing I generally prefer static typing, due to compile type checking, better documented code,etc. However I do agree that they do clutter up the code if done the way Java does it, for example. so Im about to start building a language of my own and type inference is one of the things that I want to implement, in a functional style language... I do understand that it is a big subject, and Im not trying to create something that has not been done before, just basic inferencing... any pointers on what to read up that will help me with this? preferably something more pragmatic/practical as oppose to more theoretical category theory/type theory texts. If there's a implementation discussion text out here, with data structures/algorithms, that would just be lovely much appreciated

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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