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• How to create a custom ADO Multi Dimensional Catalog with no database

  - by Alan Clark

  Does anyone know of an example of how to dynamically define and build ADO MD (ActiveX Data Objects Multidimensional) catalogs and cube definitions with a set of data other than a database? Background: we have a huge amount of data in our application that we export to a database and then query using the usual SQL joins, groups, sums etc to produce reports. The data in the application is originally in objects and arrays. The problem is the amount of data is so large the export can take 2 hours. So I am trying to figure out a good way of querying the objects in memory, either by a custom OLAP algorithm or library, or ADO MD. But I haven't been able to find an example of using ADO MD without a database behind it. We are using Delphi 2010 so would use ADO ActiveX but I imagine the ADO.NET MD is similar. I realize that if the application data was already stored in a database the problem would solve itself. Also if Delphi had LINQ capability I could query the objects and arrays that way.

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• How to use DoG Pyramid in SIFT

  - by Ahmet Keskin

  Hi all, I am very new in image processing and pattern recognition. I am trying to implement SIFT algorithm where I am able to create the DoG pyramid and identify the local maximum or minimum in each octave. What I don't understand is that how to use these local max/min in each octave. How do I combine these points? My question may sound very trivial. I have read Lowe's paper, but could not really understand what he did after he built the DoG pyramid. Any help is appreciated. Thank you

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• Rotation Interpolation

  - by Rob

  Hello, NB: I'll present this question in degrees purely for simplicity, radians, degrees, different zero-bearing, the problem is essentially the same. Does anyone have any ideas on the code behind rotational interpolation? Given a linear interpolation function: Lerp(from, to, amount), where amount is 0...1 which returns a value between from and to, by amount. How could I apply this same function to a rotational interpolation between 0 and 360 degrees? Given that degrees should not be returned outside 0 and 360. Given this unit circle for degrees: where from = 45 and to = 315, the algorithm should take the shortest path to the angle, i.e. it should go through zero, to 360 and then to 315 - and not all the way round 90, 180, 270 to 315. Is there a nice way to achieve this? Or is it going to just be a horrid mess of if() blocks? Am I missing some well understood standard way of doing this? Any help would be appreciated.

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• How can I refactor this to use an inline function or template instead of a macro?

  - by BillyONeal

  Hello, everyone :) I have a useful macro here: #define PATH_PREFIX_RESOLVE(path, prefix, environment) \ if (boost::algorithm::istarts_with(path, prefix)) { \ ExpandEnvironmentStringsW(environment, buffer, MAX_PATH); \ path.replace(0, (sizeof(prefix)/sizeof(wchar_t)) - 1, buffer); \ if (Exists(path)) return path; \ } It's used about 6 times within the scope of a single function (that's it), but macros seem to have "bad karma" :P Anyway, the problem here is the sizeof(prefix) part of the macro. If I just replace this with a function taking a const wchar_t[], then the sizeof() will fail to deliver expected results. Simply adding a size member doesn't really solve the problem either. Making the user supply the size of the constant literal also results in a mess of duplicated constants at the call site. Any ideas on this one?

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• Java Future and infinite computation

  - by Chris

  I'm trying to optimize an (infinite) computation algorithm. I have an infinte Sum to calculate ( Summ_{n- infinity} (....) ) My idea was to create several threads using the Future < construct, then combine the intermediate results together. My problem hoewer is that I need a certain precision. So I need to constantly calculate the current result while other threads keep calculating. My question is: Is there some sort of result queue where each finished thread can put its results in, while a main thread can receive those results and then either lets the computation continues or terminate the whole ExecutorService? Any Help would really be appreciated! Thanks!

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• The fastest way to do a collection subtraction

  - by Tony

  I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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• In Subversion, I know when a file was added, what's the quickest way to find out when it was deleted

  - by Eric Johnson

  OK, so suppose I know I added file "foo.txt" to my Subversion repository at revision 500. So I can do a svn log -v http://svnrepo/path/foo.txt@500, and that shows all the files added at the same time. What's the fastest way to find when the file was deleted after it was added? I tried svn log -r500:HEAD -v http://svnrepo/path/foo.txt@500, but that gives me "path not found" - perhaps obviously, because the file "foo.txt" doesn't exist at "HEAD". I can try a binary search algorithm going forward through revisions (and that would certainly be faster than typing this question), but is there a better way?

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• [java] Efficiency of while(true) ServerSocket Listen

  - by Submerged

  I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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• LINQ Quicksort is Unstable Except When Cascading

  - by Mystagogue

  On page 64 of "LINQ To Objects Using C# 4.0" (Tony Magennis) he states that LINQ's quicksort ordering algorithm is unstable... ...although this is simply solved by cascading the result into a ThenBy or ThenByDescending operator. Huh? Why would cascading an unstable sortation into another sortation fix the result? In fact, I'd say that isn't possible. The original order, once passed through an unstable sort, is simply lost. What am I missing here?

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• Key stroke time in Openmoko or any smart phones

  - by Adi

  Dear all, I am doing a project in which I am working on security issues related to smart phones. I want to develop an authentication scheme which is based on biometrics, Every human being have a unique key-hold time,digraph time error rate. Key-Hold Time : Time difference between pressing and releasing a key . Digraph Time : Time difference between releasing one and pressing next one. Error Rate : No of times backspace is pressed. I got these metrics from a paper "Keystroke-based User Identification on Smart Phones" by Saira Zahid1, Muhammad Shahzad1, Syed Ali Khayam1,2, Muddassar Farooq1. I was planning to get the datasets to test my algorithm from openmoko phone, but the phone is mis-behaving and I am finding trouble in generating these time data-sets. If anyone can help me or tell me a good source of data sets for the 3 metrics I defined, it will be a great help. Thanks Aditya

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• Intra-Unicode "lean" Encoding Converters

  - by Mystagogue

  Windows provides encoding conversion functions ("MultiByteToWideChar" and "WideCharToMultiByte") which are capable of UTF-8 to/from UTF-16 conversions, among other things. But I've seen people offer home-grown 30 to 40 line functions that claim also to perform UTF-8 / UTF-16 encoding conversions. My question is, how reliable are such tiny converters? Can such a tiny amount of code handle problems such as converting a UTF-16 surrogate pair (such as ) into a UTF-8 single four byte sequence (rather than making the mistake of converting into a pair of three byte sequences)? Can they correctly spot "unpaired" surrogate input, and provide an error? In short, are such tiny converters mere toys, or can they be taken seriously? For that matter, why does unicode.org seemingly offer no advice on an algorithm for accomplishing such conversions?

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• NSString stringWithFormat: with C array?

  - by Chris Long

  Hi, I'm writing a program that calculates the Jacobi algorithm. It's written in Objective-C since it runs on a Mac, but the majority is written in standard C. I'm using a two-dimensional C array and an NSArray containing 5 NSTextField labels. The following code yields an EXC_BAD_ACCESS error: for ( int i = 0; i < 5; i++ ) { NSString *resultString = [NSString stringWithFormat:@"%g", matrix[i][i] ]; [[resultLabels objectAtIndex:i] setStringValue:resultString]; // error line } Any help?

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• Edit Distance in Python

  - by Alice

  I'm programming a spellcheck program in Python. I have a list of valid words (the dictionary) and I need to output a list of words from this dictionary that have an edit distance of 2 from a given invalid word. I know I need to start by generating a list with an edit distance of one from the invalid word(and then run that again on all the generated words). I have three methods, inserts(...), deletions(...) and changes(...) that should output a list of words with an edit distance of 1, where inserts outputs all valid words with one more letter than the given word, deletions outputs all valid words with one less letter, and changes outputs all valid words with one different letter. I've checked a bunch of places but I can't seem to find an algorithm that describes this process. All the ideas I've come up with involve looping through the dictionary list multiple times, which would be extremely time consuming. If anyone could offer some insight, I'd be extremely grateful. Thanks!

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• Java RandomAccessFile - dealing with different newline styles?

  - by waitinforatrain

  Hey, I'm trying to seek through a RandomAccessFile, and as part of an algorithm I have to read a line, and then seek backwards from the end of the line E.g String line = raf.readLine(); raf.seek (raf.getFilePointer() - line.length() + m.start() + m.group().length()); //m is a Matcher for regular expressions I've been getting loads of off-by-one errors and couldn't figure out why. I just discovered it's because some files I'm reading from have UNIX-style linefeeds, \r\n, and some have just windows-style \n. Is there an easy to have the RandomAccessFile treat all linefeeds as windows-style linefeeds?

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• Error Creating View From Importing MysqlDump

  - by Joshua

  I don't speak SQL... Please, anybody help me. What does this mean?: Error SQL query: /*!50001 CREATE ALGORITHM=UNDEFINED *//*!50001 VIEW `v_sr_videntity` AS select `t`.`c_id` AS `ID`,`User`.`c_id` AS `UserID`,`videntityfingerprint`.`ID` AS `VIdentityFingerPrintID`,`videntityfingerprint`.`FingerPrintID` AS `FingerPrintID`,`videntityfingerprint`.`FingerPrintFingerPrint` AS `FingerPrintFingerPrint` from ((`t_SR_u_Identity` `t` join `t_SR_u_User` `User` on((`User`.`c_r_Identity` = `t`.`c_id`))) join `vi_sr_videntity_0` `VIdentityFingerPrint` on((`videntityfingerprint`.`c_r_Identity` = `t`.`c_id`))) */; MySQL said: #1054 - Unknown column 'videntityfingerprint.ID' in 'field list' What does this mean? What is it expecting? How do I fix it? This file was created by mysqldump, so why are there errors when I import it?

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• iphone sdk conditional in switch function

  - by Oliver

  I'm trying to make a random image appear on the press of a button. So it generates a random number, and the switch algorithm swaps the chosen image with the one in the imgview. but I want a switch in the settings app to toggle which set of images to use. I know pretty much how to do it...it's just that it doesn't work. I'm missing some syntax thing...Please help, stackoverflow? it's my birthday. int Number = rand() %30; NSString *toggleValue = [[NSUserDefaults standardUserDefaults] stringForKey:@"enabled_preference"]; switch (Number) { if (*toggleValue == 0) { case 0: picture.image = [UIImage imageNamed:@"1.png"]; break; case 1: picture.image = [UIImage imageNamed:@"2.png"]; break;} else { case 0: picture.image = [UIImage imageNamed:@"3.png"]; break; case 1: picture.image = [UIImage imageNamed:@"4.png"]; break;} }

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• How to perform a literal match with regex using wildcard

  - by kashif4u

  I am trying to perform literal match with regular expression using wildcard. string utterance = "Show me customer id 19"; string pattern 1 = "*tom*"; string patter 2 = "*customer id [0-9]*"; Desired results: if (Regex.IsMatch(utterance, pattern 1 )) { MATCH NOT FOUND } if (Regex.IsMatch(utterance, pattern 2 )) { MATCH FOUND } I have tried looking for literal match solution/syntax in wildcard but having difficulty. Could you also enlighten me with with an example on possible Pattern Matching Strength algorithm i.e. if code match 90 select? Note: I have table with 100000 records to perform literal matches from user utterances. Thanks in advance.

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• Using hash functions with Bloom filters

  - by dangerstat

  Hi, A bloom filter uses a hash function (or many) to generate a value between 0 and m given an input string X. My question is how to you use a hash function to generate a value in this way, for example an MD5 hash is typically represented by a 32 length hex string, how would I use an MD5 hashing algorithm to generate a value between 0 and m where I can specify m? I'm using Java at the moment so an example of to do this with the MessageDigest functionality it offers would be great, though just a generic description of how to do about it would be fine too. Thanks

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• HowTo make a marching ants border in Morphic?

  - by Helene Bilbo

  I am looking for a marching ants border or line in Morphic: Wikipedia describes a possbile algorithm: The easiest way to achieve this animation is by drawing the selection using a pen pattern that contains diagonal lines. If the selection outline is only one pixel thick, the slices out of the pattern will then look like a dashed line, and the animation can easily be achieved by simply shifting the pattern one pixel sideways and redrawing the outline. As there is probably none readymade, has anybody a hint for me how to create such a border or line? (The marching ants pattern as a GIF animation is licensed under CC by Uli Kusterer)

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• Python KMeans clustering words

  - by sadawd

  Dear Everyone I am interested to perform kmeans clustering on a list of words with the distance measure being Leveshtein. 1) I know there are a lot of frameworks out there, including scipy and orange that has a kmeans implementation. However they all require some sort of vector as the data which doesn't really fit me. 2) I need a good clustering implementation. I looked at python-clustering and realize that it doesn't a) return the sum of all the distance to each centroid, and b) it doesn't have any sort of iteration limit or cut off which ensures the quality of the clustering. python-clustering and the clustering algorithm on daniweb doesn't really work for me. Can someone find me a good lib? Google hasn't been my friend

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• Encrypt/Decrypt SQLite-database and use it "on the fly"

  - by Berschi

  Here's the thing: In my Qt4.6-Project, I use a SQLite-Database. This database shouldn't be unencrypted on my harddrive. So I want, that on every start of my program, the user gets asked to enter a password to decrypt the database. Of course the database never should appear "in clear" (not encrypted) on my harddrive. So is there any possibility to decrypt a SQLite-database "on the fly" and read and write data? What algorithm is here the best (maybe AES)? When it's not possible (or very slow), maybe it's better to encrypt every string in the database and decrypt the string when the password was right (so that a user could open the database, but has no clue what all the entrys could mean)?

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• Simple but efficient way to store a series of small changes to an image?

  - by finnw

  I have a series of images. Each one is typically (but not always) similar to the previous one, with 3 or 4 small rectangular regions updated. I need to record these changes using a minimum of disk space. The source images are not compressed, but I would like the deltas to be compressed. I need to be able to recreate the images exactly as input (so a lossy video codec is not appropriate.) I am thinking of something along the lines of: Composite the new image with a negative of the old image Save the composited image in any common format that can compress using RLE (probably PNG.) Recreate the second image by compositing the previous image with the delta. Although the images have an alpha channel, I can ignore it for the purposes of this function. Is there an easy-to-implement algorithm or free Java library with this capability?

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• Need help using the Windows IP Helper API & ParseNetworString in C#.

  - by JohnnyNoir

  I'm attempting to rewrite some C# web service code that uses the Windows IP Helper API call "SendARP" to retreive a remote system's MAC address. SendARP works great - until you cross a network segment as Arp requests aren't routed. I've been looking at the "ParseNetworkString" documentation after happening across its existance on StackOverflow. The quick & dirty algorithm I have in mind is: public static string GetMacAddress(string strHostOrIP) { if (strHostOrIP is IPAddress) { parse results of nbstat -A strHostOrIP return macAddress } if (strHostOrIP is Hostname) { IPHostEntry hostEntry = null; try { hostEntry = Dns.GetHostEntry(strHostOrIP); } catch { return null; } if (hostEntry.AddressList.Length == 0) { return null; } foreach (IPAddress ip in hostEntry.AddressList) { if (ip.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork) { ipAddress = ip; break; } } } return GetMACAddress(ipAddress); } "ParseNetworkString" is new with Vista/Win2008 so I haven't been able to find example C# code demonstrating its use and I'm no C++ coder so if anyone can point me in the right direction...

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• Guiding a Robot Through a Path

  - by Hamza Yerlikaya

  I have a field filled with obstacles, I know where they are located, and I know the robot's position. Using a path-finding algorithm, I calculate a path for the robot to follow. Now my problem is, I am guiding the robot from grid to grid but this creates a not-so-smooth motion. I start at A, turn the nose to point B, move straight until I reach point B, rinse and repeat until the final point is reached. So my question is: What kind of techniques are used for navigating in such an environment so that I get a smooth motion? The robot has two wheels and two motors. I change the direction of the motor by turning the motors in reverse. EDIT: I can vary the speed of the motors basically the robot is an arduino plus ardumoto, I can supply values between 0-255 to the motors on either direction.

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• Recursive vs. Iterative algorithms

  - by teehoo

  I'm implementing the Euclidian algorithm for finding the GCD (Greatest Common Divisor) of two integers. Two sample implementations are given: Recursive and Iterative. http://en.wikipedia.org/wiki/Euclidean_algorithm#Implementations My Question: In school I remember my professors talking about recursive functions like they were all the rage, but I have one doubt. Compared to an iterative version don't recursive algorithms take up more stack space and therefore much more memory? Also, because calling a function requires uses some overhead for initialization, aren't recursive algorithms more slower than their iterative counterpart?

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