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• How to reduce the number of points in (x,y) data

  - by Gowtham

  I have a set of data points: (x1, y1) (x2, y2) (x3, y3) ... (xn, yn) The number of sample points can be thousands. I want to represent the same curve as accurately as possible with minimal (lets suppose 30) set of points. I want to capture as many inflection points as possible. However, I have a hard limit on the number of allowed points to represent the data. What is the best algorithm to achieve the same? Is there any free software library that can help? PS: I have tried to implement relative slope difference based point elimination, but this does not always result in the best possible data representation. Thanks for your time. -Gowtham

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• NASM: Count how many bits in a 32 Bit number are set to 1.

  - by citronas

  I have a 32 Bit number and want to count know how many bits are 1. I'm thinking of this pseudocode: mov eax, [number] while(eax != 0) { div eax, 2 if(edx == 1) { ecx++; } shr eax, 1 } Is there a more efficient way? I'm using NASM on a x86 processor. (I'm just beginning with assembler, so please do not tell me to use code from extern libraries, because I do not even know how to include them ;) ) (I just found http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer which also contains my solution. There are other solutions posted, but unfortunatly I can't seem to figure out, how I would write them in assembler)

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• Extracting data points from a matrix and saving them in different matrixes in MATLAB

  - by Hossein

  Hi, I have a 2D Matrix consisting of some coordinates as below(example): Data(X,Y): 45.987543423,5.35000964 52.987544223,5,98765234 Also I have an array consisting of some integers =0 , for example: Cluster(M) 2,0,3,1 each of these numbers in this array corresponds with a row of my 2D Matrix above.For example, it says that row one(coordinate) in the Data Matirx belongs to the cluster 2,second row belongs to cluster 0 and so on. Now I want to have each of the datapoint of each cluster in a separate matrix, for example I want to save datapoints belonging to cluster 1 in a separate matrix, cluster 2 in a separate matrix and so on,.... I can do them manually, but the problem is this has to be an automatic extraction. which means that the number of clusters(range of the numbers in the cluster array varies in each run) so I have to have a general algorithm that does this extraction for me. Can someone help me please? 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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• Serial numbers generation without user data

  - by Sphynx

  This is a followup to this question. The accepted answer is generally sufficient, but requires user to supply personal information (e.g. name) for generating the key. I'm wondering if it's possible to generate different keys based on a common seed, in a way that program would be able to validate if those keys belong to particular product, but without making this process obvious to the end user. I mean it could be a hash of product ID plus some random sequence of characters, but that would allow user to guess potential new keys. There should be some sort of algorithm difficult to guess.

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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: 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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• Rearrange a python list into n lists, by column

  - by Ben R

  Trying to solve this at this hour has gotten my mind into a tail-spin: I want to rearrange a list l into a list of n lists, where n is the number of columns. e.g., l = [1,2,3,4,5,6,7,8] n = 5 ==> [[1,6][2,7][3,8][4][5]] another example: l = [1,2,3,4,5,6,7,8,9,10] n = 4 ==> [[1,5,9],[2,6,10],[3,7][4,8] Can someone please help me out with an algorithm? Feel free to use any python awesomeness that's available; I'm sure theres some cool mechanism that's a good fit for this, i just can't think of it.

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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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• When to trash hashmap contents to avoid performance degradation?

  - by Jack

  Hello, I'm woking on Java with a large (millions) hashmap that is actually built with a capacity of 10.000.000 and a load factor of .75 and it's used to cache some values since cached values become useless with time (not accessed anymore) but I can't remove useless ones while on the way I would like to entirely empty the cache when its performance starts to degrade. How can I decide when it's good to do it? For example, with 10 millions capacity and .75 should I empty it when it reaches 7.5 millions of elements? Because I tried various threshold values but I would like to have an analytic one. I've already tested the fact that emping it when it's quite full is a boost for perfomance (first 2-3 algorithm iterations after the wipe just fill it back, then it starts running faster than before the wipe) Thanks

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• How do I restrict the WCF service called by an ASP.NET AJAX page to only allow calls for that page?

  - by NovaJoe

  I have an AjaxControlToolkit DynamicPopulate control that is updated by calls to a WCF service. I know I can check the HttpContext in the service request to see if a user of the page (and thus, the control) is authenticated. However, I don't want anyone clever to be able to call the service directly, even if they're logged in. I want access to the service to be allowed ONLY to requests that are made from the page. Mainly, I don't want anyone to be able to programatically make a large number of calls and then reverse-engineer the algorithm that sits behind the service. Any clever ideas on how this can be done? Maybe I'm over-thinking this? Thanks in advance.

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• Use CSS selectors to collect HTML elements from a streaming parser (e.g. SAX stream)

  - by Jakub Narebski

  How to parse CSS (CSS3) selector and use it (in jQuery-like way) to collect HTML elements not from DOM (from tree structure), but from stream (e.g. SAX), i.e. using sequential access parser? Are there CSS selectors that need access to DOM (Wikipedia SAX page says that XPath selectors "need to be able to access any node at any time in the parsed XML tree")? I am most inetersted in implementing selector combinators, e.g. 'A B' descendant selector. I prefer solutions describing algorithm, or in Perl.

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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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• 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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• Is it possible to manipulate the format on a DataGridView that is bound to a Data Source?

  - by Jack Johnstone

  I´m using SQL Server 2005 and Visual Studio 2008, C#. In the data source (the SQL Server data table) I use the date format mm/dd/yyyy, however, in a forms overview (DataGridView) users would like to see a completely other format, with year, week number and day number of week (yyww,d). I´ve created an algorithm for this transformation, but can I populate the affected cells with yyww,d instead of mm/dd/yyyy? And in that case - how would I do it? I guess I need to do it after the cells are populated, but before they are shown. The generic question is - how do I manipulate the format of Data Source bound DataGridView cells.

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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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• 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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• 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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• 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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• Selecting item from set given distribution

  - by JH

  I have a set of X items such as {blower, mower, stove} and each item has a certain percentage of times it should be selected from the overall set {blower=25%,mower=25%,stove=75%} along with a certain distribution that these items should follow (blower should be selected more at the beginning of selection and stove more at the end). We are given a number of objects to be overall selected (ie 100) and a overall time to do this in (say 100 seconds). I was thinking of using a roulette wheel algorithm where the weights on the wheel are affected by the current distribution as a function of the elapsed time (and the allowed duration) so that simple functions could be used to determine the weight. Are there any common approaches to problems like this that anyone is aware of? Currently i have programmed something similar to this in java using functions such as x^2 (with correct normalization for the weights) to ensure that a good distribution occurs. Other suggestions or common practices would be welcome :-)

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• Search pattern in string using regex in obj-c

  - by manileo86

  I'm working on a string pattern match algorithm. I use NSRegularExpression for finding the matches. For ex: I've to find all words starting with '#' in a string.. Currently I use the following regex function: static NSRegularExpression *_searchTagRegularExpression; static inline NSRegularExpression * SearchTagRegularExpression() { if (!_searchTagRegularExpression) { _searchTagRegularExpression = [[NSRegularExpression alloc] initWithPattern:@"(?<!\\w)#([\\w\\._-]+)? options:NSRegularExpressionCaseInsensitive error:nil]; } return _searchTagRegularExpression; } and I use it as below: NSRegularExpression *regexp = SearchTagRegularExpression(); [regexp enumerateMatchesInString:searchString options:0 range:stringRange usingBlock:^(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop) { // comes here for every match with range }]; This works properly. But i just want to know if this is the best way. suggest if there's any better alternative...

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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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• 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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• 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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• Architecture of a secure application that encrypts data in the database.

  - by Przemyslaw Rózycki

  I need to design an application that protects some data in a database against root attack. It means, that even if the aggressor takes control over the machine where data is stored or machine with the application server, he can't read some business critical data from the database. This is a customer's requirement. I'm going to encrypt data with some assymetric algorithm and I need some good ideas, where to store private keys, so that data is secure as well as the application usability was quite comfortable? We can assume, for simplicity, that only one key pair is used.

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