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• Lua: Random: Percentage

  - by jargl

  I'm creating a game and currently have to deal with some math.randomness. As I'm not that strong in Lua, how do you think Can you make an algorithm that uses math.random with a given percentage? I mean a function like this: function randomChance( chance ) -- Magic happens here -- Return either 0 or 1 based on the results of math.random end randomChance( 50 ) -- Like a 50-50 chance of "winning", should result in something like math.random( 1, 2 ) == 1 (?) randomChance(20) -- 20% chance to result in a 1 randomChance(0) -- Result always is 0 However I have no clue how to go on, and I completely suck at algorithms I hope you understood my bad explanation of what I'm trying to accomplish

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• [PHP] - Lowering script memory usage in a "big" file creation

  - by Riccardo

  Hi there people, it looks like I'm facing a typical memory outage problem when using a PHP script. The script, originally developed by another person, serves as an XML sitemap creator, and on large websites uses quite a lot of memory. I thought that the problem was related due to an algorithm holding data in memory until the job was done, but digging into the code I have discovered that the script works in this way: open file in output (will contain XML sitemap entries) in the loop: ---- for each entry to be added in sitemap, do fwrite close file end Although there are no huge arrays or variables being kept in memory, this technique uses a lot of memory. I thought that maybe PHP was buffering under the hood the fwrites and "flushing" data at the end of the script, so I have modified the code to close and open the file every Nth record, but the memory usage is still the same.... I'm debugging the script on my computer and watching memory usage: while script execution runs, memory allocation grows. Is there a particular technique to instruct PHP to free unsed memory, to force flushing buffers if any? Thanks

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• saving file name from html form input

  - by user343934

  I am working on python and biopython right now. I have a file upload form and whatever file is uploaded suppose(abc.fasta) then i want to pass same name in execute (abc.fasta) function parameter and display function parameter (abc.aln). Workflow goes like this. ----If submit is not true then display only header and form part --- if submit is true then call execute() and get file name from form input --- Then display the save file result in the same page. File name is same as input. My raw code is here -- http://pastebin.com/FPUgZSSe Any suggestions, changes and algorithm is appreciated Thanks

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• Need to get pixel averages of a vector sitting on a bitmap...

  - by user346511

  I'm currently involved in a hardware project where I am mapping triangular shaped LED to traditional bitmap images. I'd like to overlay a triangle vector onto an image and get the average pixel data within the bounds of that vector. However, I'm unfamiliar with the math needed to calculate this. Does anyone have an algorithm or a link that could send me in the right direction? I'm not even clear what this type of math is called. I've created a basic image of what I'm trying to capture here: http://imgur.com/Isjip.gif

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• MATLAB: draw centroids

  - by Myx

  Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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• PHP: Loop through text file and isolate lines which a specific "starting point"

  - by Mestika

  Hi everyone, I’m trying to reduce some editing time within some textfiles where there approximately are 10.000 lines of text, but I only need around 200 or some. The text file relies on a almost specific pattern but it deviates from time to time but my “focus” in order to select the right line to keep is, that the line always starts with: z3455 and then have a variable afterwards, e.g.: z3455 http://url.com/data1/data1.1/data1.3/ (342kb) I have an algorithm to capture the URL and its content but now I need some way to loop through the text file, deleting all lines except does that starts with z3455 and then “push” them together so they are listed underneath each other. I’ve tried different approaches for this in PHP but can’t seem to find a correct function. I can “isolate” a specific line number but when it deviates I can’t use this approach fully. I hope that someone can help me, either by providing the code or knocking me in the right direction to how I’ll solve this problem. Thanks in advance Sincerely - Mestika

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• Matching a rotated bitmap to a collage image

  - by Dmi

  Hi, My problem is that I have an image of a detailed street map. On this map, there can be a certain small image of a sign (such as a traffic light icon) rotated at any angle, maybe resized. I have this small image in a bitmap. Is there any algorithm or technique by which I can locate this bitmap if a copy of it exists, rotated and maybe resized, in the large collage image? This is similar to the problem with Augmented Reality and locating the marker image, but mine is only 2D with no perspective distortion.

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• make a lazy var in scala

  - by ayvango

  Scala does not permit to create laze vars, only lazy vals. It make sense. But I've bumped on use case, where I'd like to have similar capability. I need a lazy variable holder. It may be assigned a value that should be calculated by time-consuming algorithm. But it may be later reassigned to another value and I'd like not to call first value calculation at all. Example assuming there is some magic var definition lazy var value : Int = _ val calc1 : () => Int = ... // some calculation val calc2 : () => Int = ... // other calculation value = calc1 value = calc2 val result : Int = value + 1 This piece of code should only call calc2(), not calc1 I have an idea how I can write this container with implicit conversions and and special container class. I'm curios if is there any embedded scala feature that doesn't require me write unnecessary code

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• F# replace ref variable with something fun

  - by Stephen Swensen

  I have the following F# functions which makes use of a ref variable to seed and keep track of a running total, something tells me this isn't in the spirit of fp or even particular clear on its own. I'd like some direction on the clearest (possible fp, but if an imperative approach is clearer I'd be open to that) way to express this in F#. Note that selectItem implements a random weighted selection algorithm. type WeightedItem(id: int, weight: int) = member self.id = id member self.weight = weight let selectItem (items: WeightedItem list) (rand:System.Random) = let totalWeight = List.sumBy (fun (item: WeightedItem) -> item.weight) items let selection = rand.Next(totalWeight) + 1 let runningWeight = ref 0 List.find (fun (item: WeightedItem) -> runningWeight := !runningWeight + item.weight !runningWeight >= selection) items let items = [new WeightedItem(1,100); new WeightedItem(2,50); new WeightedItem(3,25)] let selection = selectItem items (new System.Random())

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• The easiest way to draw an image?

  - by Benno

  Assume you want to read an image file in a common file format from the hard drive, change the color of one pixel, and display the resulting image to the screen, in C++. Which (open-source) libraries would you recommend to accomplish the above with the least amount of code? Alternatively, which libraries would do the above in the most elegant way possible? A bit of background: I have been reading a lot of computer graphics literature recently, and there are lots of relatively easy, pixel-based algorithms which I'd like to implement. However, while the algorithm itself would usually be straightforward to implement, the necessary amount of frame-work to manipulate an image on a per-pixel basis and display the result stopped me from doing it.

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• R: how to make a unique set of names from a vector of strings?

  - by Mike Dewar

  Hi, I have a vector of strings. Check out my vector, it's awesome: > awesome [1] "a" "b" "c" "d" "d" "e" "f" "f" I'd like to make a new vector that is the same length as awesome but where, if necessary, the strings have been uniqueified. For example, a valid output of my desired function would be > awesome.uniqueified [1] "a" "b" "c" "d.1" "d.2" "e" "f.1" "f.2" Is there an easy, R-thonic and beautiful way to do this? I should say my list in real life (it's not called awesome) contains 25000ish mircoarray probeset identifiers. I'm always nervous when I embark on writing little generic functions (which I'm sure I could do) as I'm sure some R guru has come across this problem in the past, nailed it with some incredible algorithm that doesn't even have to store more than half an element in the vector. I'm just not sure what they might have called it. Probably not uniqueify.

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• finding the total number of distinct shortest paths between 2 nodes in undirected weighted graph in linear time?

  - by logan

  I was wondering, that if there is a weighted graph G(V,E), and I need to find a single shortest path between any two vertices S and T in it then I could have used the Dijkstras algorithm. but I am not sure how this can be done when we need to find all the distinct shortest paths from S to T. Is it solvable on O(n) time? I had one more question like if we assume that the weights of the edges in the graph can assume values only in certain range lets say 1 <=w(e)<=2 will this effect the time complexity?

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• PHP: Safe way to store decryptable passwords

  - by Jammer

  I'm making an application in PHP and there is a requirement that it must be possible to decrypt the passwords in order to avoid problems in the future with switching user database to different system. What encryption/decryption algorithm would you suggest? Is it good idea to just store the encrypted value and then compare the future authentication attempts to that value? Are the passwords still as safe as MD5/SHA1 when the private key is not available to the attacker (Hidden in USB drive for example)? I should still use salting, right? What encryption libraries should I use for PHP?

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• Alternative to latex / a way to typeset good looking documents from Java to PDF

  - by drasto

  I'm working on application in Java that will maintain database of song lyrics in plain text and print out some songbooks/chordbooks(that is create PDF file from selected songs). I was planing that the Java application will generate source code for pdflatex and after compiling this source user will get PDF file. Lately I've run into a lot of problems because of latex limitation: fixed memory size (some pictures will also be drawn to PDF) - error when exceeded, no way to query end of line or and of page dynamically, it's very hard to override latex placement algorithm in a complex way,... see also some my other questions regarding latex. I come to conclusion that latex is not good option for automated PDF generation. So I need replacement. I need to be able to typeset: Chords over lyrics when the lyrics are in variable char width so I need to be able to measure text width Chord diagrams that means I'll have to draw quite complex pictures Each song on separate double page Different fonts etc. Thanks for all answers

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• Measure CPU performance via JS

  - by Nicholas Kyriakides

  A webapp has as a central component a relatively heavy algorithm that handles geometric operations. There are 2 solutions to make the whole thing accessible from both high-end machines and relatively slower mobile devices. I will use RPC's if i detect that the user machine is ''slow'' or else if i detect that the user machine can handle it OK, then i provide to the webapp the script to handle it client side. Now what would be a reliable way to detect the speed of the user machine? I was thinking of providing a sample script as a test when the page loads and detect the time it took to execute that. Any ideas?

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• How to test Text Search accuracy and efficiency?

  - by DEN

  I have created a web application. One of the feature is text search which perform the boolean operator ( NOT, AND, OR) as well. However, I have no idea on calculating the search's accuracy and efficiency. For example: 1 . Probe identification system for a measurement instrument 2 . Pulse-based impedance measurement instrument 3 . Millimeter with filtered measurement mode when the user key in will return the result as below input :measurement instrument Result: 1,2 input : measurement OR instrument NOT milimeter Result: 1,2,3 so, i have no idea on what issue and what algorithm to calculate on the accuracy and efficiency of the text search.. anyone have any idea on that?

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• function to efficiently check a change of value in a nested hashmap

  - by zcaudate

  the motivation is for checking what has changed in a deeply nest map, kind of like a reverse of update-in. This is a simple example: (def p1 {:a {:a1 :1 :a2 :2} :b {:b1 :1 :b2 :2}}) (def p2 (update-in p1 [:a :a1] (constantly :updated)) ;; => {:a {:a1 :updated :a2 :2} ;; :b {:b1 :1 :b2 :2}} (what-changed? p1 p2) ;; => {:keys [:a :a1] :value :updated) (what-changed? p2 p1) ;; => {:keys [:a :a1] :value :2) I'm hoping that because clojure maps are persistent data-structures, there may be a smart algorithm to figure this out by looking at the underlying structure as opposed to walking through the nested maps and comparing the difference.

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• 0.20.2 API hadoop version with java 5

  - by abdeslam

  I have started a maven project trying to implement the MapReduce algorithm in java 1.5.0_14. I have chosen the 0.20.2 API hadoop version. In the pom.xml i'm using thus the following dependency: < dependency < groupId>org.apache.hadoop< /groupId> < artifactId>hadoop-core< /artifactId> < version>0.20.2< /version> < /dependency But when I'm using an import to the org.apache.hadoop classes, I get the following error: bad class file: ${HOME_DIR}\repository\org\apache\hadoop\hadoop-core\0.20.2\hadoop-core-0.20.2.jar(org/apache/hadoop/fs/Path.class) class file has wrong version 50.0, should be 49.0. Does someone know how can I solve this issue. Thanks.

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• Generating a beveled edge for a 2D polygon

  - by Metaphile

  I'm trying to programmatically generate beveled edges for geometric polygons. For example, given an array of 4 vertices defining a square, I want to generate something like this. But computing the vertices of the inner shape is baffling me. Simply creating a copy of the original shape and then scaling it down will not produce the desired result most of the time. My algorithm so far involves analyzing adjacent edges (triples of vertices; e.g., the bottom-left, top-left, and top-right vertices of a square). From there, I need to find the angle between them, and then create a vertex somewhere along that angle, depending on how deep I want the bevel to be. And because I don't have much of a math background, that's where I'm stuck. How do I find that center angle? Or is there a much simpler way of attacking this problem?

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• C++ - defining static const integer members in class definition

  - by HighCommander4

  My understanding is that C++ allows static const members to be defined inside a class so long as it's an integer type. Why, then, does the following code give me a linker error? #include <algorithm> #include <iostream> class test { public: static const int N = 10; }; int main() { std::cout << test::N << "\n"; std::min(9, test::N); } The error I get is: test.cpp:(.text+0x130): undefined reference to `test::N' collect2: ld returned 1 exit status Interestingly, if I comment out the call to std::min, the code compiles and links just fine (even though test::N is also referenced on the previous line). Any idea as to what's going on? My compiler is gcc 4.4 on Linux.

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• Why do debug symbols so adversely affect the performance of threaded applications on Linux?

  - by fluffels

  Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?

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• Why is C++ fwrite() producing larger output in release?

  - by waffleShirt

  I recently wrote an implementation of the Canonical Huffman compression algorithm. I have a 500kb test file that can be compressed to about 250kb when running the debug and release builds from within Visual Studio 2008. However when I run the release build straight from the executeable the test file only compresses to about 330kb. I am assuming that something is going wrong when the file is written using fwrite(). I have tested the program and confirmed that uncompressing the files always produces the correct uncompressed file. Does anyone know why this could possibly be? How could the same executeable file be producing different sized outputs based on where it is launched from?

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• Beginner C: error: control reaches end of non-void function?

  - by Ting

  I'm trying to make a greedy algorithm and I get this error: greedy2.c:27:1: error: control reaches end of non-void function [-Werror,-Wreturn-type] } ^ 1 error generated. with this code: int man(int argc, char* argv[]) { float amount; do { printf("Input dollar amount owed:\n"); amount = GetFloat(); } while (amount <= 0); int coins = 0; while (amount >= 0.25); { amount = amount - 0.25; coins++; } printf("Number of coins to use: %d\n", coins); } What is wrong with my curly braces, and how do I fix it?

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• Parsing String to TreeNode

  - by Krusu70

  Anyone have a good algorithm how to parse a String to TreeNode in Java? Let's say we have a string s which says how to build a TreeNode. A(B,C) means that A is the name (String) of TreeNode, B is child of A (Treenode), C is sibling of A (TreeNode). So if I call function with string A(B(D,E(F,G)),C) (just a example), then I get a TreeNode equals to: level A (String: name), B - Child (TreeNode), C - Sibling (TreeNode) level B (String: name), D - Child of B (TreeNode), E - Sibling of B (TreeNode) level E (String: name), F - Child of E (TreeNode), G - Sibling of E (TreeNode) The name may not be 1 letter, it could be like real name (many letters).

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• UML and Documenting Simple Diagrams

  - by Jason

  As part of a rewrite of an old Java application into C#, I'm writing an actual Software Design Specification. A problem I run into is when a method is too simple to bother with a Sequence Diagram (it doesn't interact with other objects). As an example, I have a simple POJO called Item, containing the following method: public String getCategoryKey() { StringBuffer value = new StringBuffer("s-"); value.append(this.getModelID()); value.append("-c"); return value; } The purpose and the algorithm for the method needs to be documented. However, a sequence diagram is overkill. How would others document it? (I take no credit/blame for the given method, it's very old code and the author "forgot" to put their name in the Javadoc).

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