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  • MPI: is there mpi libraries capable of message compression?

    - by osgx
    Sometimes MPI is used to send low-entropy data in messages. So it can be useful to try to compress messages before sending it. I know that MPI can work on very fast networks (10 Gbit/s and more), but many MPI programs are used with cheap network like 0,1G or 1Gbit/s Ethernet and with cheap (slow, low bisection) network switch. There is a very fast Snappy (wikipedia) compression algorithm, which has Compression speed is 250 MB/s and decompression speed is 500 MB/s so on compressible data and slow network it will give some speedup. Is there any MPI library which can compress MPI messages (at layer of MPI; not the compression of ip packets like in PPP). MPI messages are also structured, so there can be some special method, like compression of exponent part in array of double.

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  • How to secure licensekey generation

    - by Jakob Gade
    Scenario, simplified for brevity: A developer creates an application for a customer. The customer sells this app to end-users. The app requires a license key to run, and this key is generated by the customer for each end-user with a simple tool created by the developer. The license key contains an expiry date for the license and is encrypted so the end-user can’t tamper with it. The problem here is that the developer (or anybody who has a copy of the license key generator) can easily create valid license keys. Should this generator fall into the wrong hands, it could spell disaster for the customers business. Ideally, the customer would have to use a password to create new license keys. And this password would be unknown to the developer, and somehow baked into the decryption algorithm in the application so it will fail if an attempt to use an unauthorized key is made. How would you implement a solution for this problem that is both transparent and secure?

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  • How do i start with Gomoku?

    - by firstTry
    I read about Gomoku that it can be implemented using Minimax and Alpha-Beta Pruning algorithms. So, i read these algorithms and now understand how the game will be solved. But when i sat to down to code, I am facing problem how to approach it. As in , How to design the prototype functions like getNextMove or Max(Move) ? How will the next move searched? Till when should i apply the minimax algorithm. I know i can find the code online, but i want to do it myself. Can anyone please point me in the right direction?

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  • Graph and permutation problem

    - by user319771
    I have a graph (with nodes and edges) containing symmetry and a group of permutations to label the nodes so no edges are changed (automorphisms). Now I would like to determine for which nodes a permutation exchanges two equivalent (i.e. nodes with the same color or symmetry class) neighboring nodes. When the nodes with equivalent neighbors stay the same, simply checking if the neighbors are exchanged in the permutation is enough. However, when the nodes with equivalent neighbors are also permuted (i.e. there are multiple nodes with the same color/symmetry class with the same equivalent neighbors), the problem becomes more complex. Is there any known algorithm for such a problem? Some remarks: The graph has no coordinates, it's a topology only

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  • What one-time-password devices are compatible with mod_authn_otp?

    - by netvope
    mod_authn_otp is an Apache web server module for two-factor authentication using one-time passwords (OTP) generated via the HOTP/OATH algorithm defined in RFC 4226. The developer's has listed only one compatible device (the Authenex's A-Key 3600) on their website. If a device is fully compliant with the standard, and it allows you to recover the token ID, it should work. However, without testing, it's hard to tell whether a device is fully compliant. Have you ever tried other devices (software or hardware) with mod_authn_otp (or other open source server-side OTP program)? If yes, please share your experience :)

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  • How do I plot the warping of DTW result using gnuplot?

    - by Ekkmanz
    Hello, Right now I have implemented Dynamic Time Warping algorithm for warping two 3D trajectories. Currently, gnuplot is my plotting tool of choice and it works fine when I plot multiple trajectories at a time. However, when I implement DTW one of the real use for plotting tool is to visualize the point warping, like this picture. Currently, the output of my DTW program is two time series in CSV files and another CSV file which indicate the warp (X in series 1 - Y in series 2). Is there any possible way to do that in gnuplot?

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  • Using boost unordered map

    - by Amrish
    Guys, I am using dynamic programming approach to solve a problem. Here is a brief overview of the approach Each value generated is identified using 25 unique keys. I use the boost::hash_combine to generate the seed for the hash table using these 25 keys. I store the values in a hash table declared as boost::unordered_map<Key_Object, Data_Object, HashFunction> hashState; I did a time profiling on my algorithm and found that nearly 95% of the run time is spent towards retrieving/inserting data into the hash table. These were the details of my hash table hashState.size() 1880 hashState.load_factor() 0.610588 hashState.bucket_count() 3079 hashState.max_size() 805306456 hashState.max_load_factor() 1 hashState.max_bucket_count() 805306457 I have the following two questions Is there anything which I can do to improve the performance of the Hash Table's insert/retrieve operations? C++ STL has hash_multimap which would also suit my requirement. How does boost libraries unordered_map compare with hash_multimap in terms of insert/retrieve performance.

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  • Spectral Reconstruction

    - by Hani
    I have a small system which consist of: Led Clusters, camera(RGB or grayscale) and an object to be detected. I am emitting a light from the LED clusters (ex: yellow). After emitting light on the object, I am capturing an image for the object from the camera. I want to get the spectral image of the object from the captured image. Please if any one knows the algorithm or a code for this purpose(grayscale or RGB camera), tell me. Thanks.....

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  • Optimizing a large iteration of PHP objects (EAV-based)

    - by Aron Rotteveel
    I am currently working on a project that utilizes the EAV model. This turns out to work quite well, but like many others I am now stumbling upon some performance issues. The data set in this particular case consists of aproximately 2500 entities, each with aprox. 150 attributes. Each entity and each attribute is represented by a PHP-object. Since most parts of the application only iterate through a filtered set of entities, we have not had very large issues yet. Now, however, I am working on an algorithm that requires iteration over the entire dataset, which causes a major impact on performance. This information is perhaps not very much to work with, but since this is an architectural problem, I am hoping for a architectural pattern to help me on the way as well. Each entity, including it's attributes takes up aprox. 500KB of memory.

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  • Fastest way to list all primes below N in python

    - by jbochi
    This is the best algorithm I could come up with after struggling with a couple of Project Euler's questions. def get_primes(n): numbers = set(range(n, 1, -1)) primes = [] while numbers: p = numbers.pop() primes.append(p) numbers.difference_update(set(range(p*2, n+1, p))) return primes >>> timeit.Timer(stmt='get_primes.get_primes(1000000)', setup='import get_primes').timeit(1) 1.1499958793645562 Can it be made even faster? EDIT: This code has a flaw: Since numbers is an unordered set, there is no guarantee that numbers.pop() will remove the lowest number from the set. Nevertheless, it works (at least for me) for some input numbers: >>> sum(get_primes(2000000)) 142913828922L #That's the correct sum of all numbers below 2 million >>> 529 in get_primes(1000) False >>> 529 in get_primes(530) True EDIT: The rank so far (pure python, no external sources, all primes below 1 million): Sundaram's Sieve implementation by myself: 327ms Daniel's Sieve: 435ms Alex's recipe from Cookbok: 710ms EDIT: ~unutbu is leading the race.

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  • Facebook App Wall Posting no longer showing in Facebook iPhone App

    - by David Hsu
    I use the GRAPH API with django for Facebook wall postings. Since yesterday, the wall posts only show on the Facebook web app but not the Facebook iPhone app. I tried Yelp, and their postings still show up. How can I debug this? Anyone notice this issue with their Facebook connect? Is this a Facebook algorithm issue. Code for Wall Post: graph = facebook.GraphAPI(access_token) attachment = {"name": name, "link": link, #"caption": "{*actor*} posted a new review", "description": desc, "picture": picture } graph.put_wall_post("",attachment)

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  • Checking for any lowercase letters in a string

    - by pcampbell
    Consider a JavaScript method that needs to check whether a given string is in all uppercase letters. The input strings are people's names. The current algorithm is to check for any lowercase letters. var check1 = "Jack Spratt"; var check2 = "BARBARA FOO-BAR"; var check3 = "JASON D'WIDGET"; var isUpper1 = HasLowercaseCharacters(check1); var isUpper2 = HasLowercaseCharacters(check2); var isUpper3 = HasLowercaseCharacters(check3); function HasLowercaseCharacters(string input) { //pattern for finding whether any lowercase alpha characters exist var allLowercase; return allLowercase.test(input); } Is a regex the best way to go here? What pattern would you use to determine whether a string has any lower case alpha characters?

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  • Difference between an LL and Recursive Descent parser?

    - by Noldorin
    I've recently being trying to teach myself how parsers (for languages/context-free grammars) work, and most of it seems to be making sense, except for one thing. I'm focusing my attention in particular on LL(k) grammars, for which the two main algorithms seem to be the LL parser (using stack/parse table) and the Recursive Descent parser (simply using recursion). As far as I can see, the recursive descent algorithm works on all LL(k) grammars and possibly more, whereas an LL parser works on all LL(k) grammars. A recursive descent parser is clearly much simpler than an LL parser to implement, however (just as an LL one is simply than an LR one). So my question is, what are the advantages/problems one might encounter when using either of the algorithms? Why might one ever pick LL over recursive descent, given that it works on the same set of grammars and is trickier to implement? Hopefully this question makes some amount of sense. Sorry if it doesn't - I blame my the fact that this entire subject is almost entirely new to me.

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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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  • Program to find canonical cover or minimum number of functional dependencies

    - by Sev
    I would like to know if there is a program or algorithm to find canonical cover or minimum number of functional dependencies? For example: If you have: R = (A,B,C) <-- these are tables: A,B,C And dependencies: A ? BC B ? C A ? B AB ? C The canonical cover (or minimum number of dependencies) is: A ? B B ? C Is there a program that can accomplish this? If not, any code/pseudocode to help me write one would be appreciated. Prefer in Python or Java.

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  • How to calculate both positive and negative angle between two lines?

    - by Jaanus
    There is a very handy set of 2d geometry utilities here. The angleBetweenLines has a problem, though. The result is always positive. I need to detect both positive and negative angles, so if one line is 15 degrees "above" or "below" the other line, the shape obviously looks different. The configuration I have is that one line remains stationary, while the other line rotates, and I need to understand what direction it is rotating in, by comparing it with the stationary line. EDIT: in response to swestrup's comment below, the situation is actually that I have a single line, and I record its starting position. The line then rotates from its starting position, and I need to calculate the angle from its starting position to current position. E.g if it has rotated clockwise, it is positive rotation; if counterclockwise, then negative. (Or vice versa.) How to improve the algorithm so it returns the angle as both positive or negative depending on how the lines are positioned?

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  • Convert XML namespace prefixes with C#?

    - by jrista
    I have run into an exasperating problem getting a Java service client to communicate successfully with a WCF service. I have overcome many hurdles, and I believe that this is my last one. The problem boils down to how Java Axis + WSS4J seem to handle xml namespaces. The Java platform seem to be very rigid in what they expect for xml namespace prefixes, and as such, do not understand the WCF reply messages. My problem in a nutshell is as follows. I have an xml response similar to the following from my WCF service: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" xmlns:a="http://www.w3.org/2005/08/addressing" xmlns:u="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"> <s:Header> <a:Action s:mustUnderstand="1" u:Id="_3">http://tempuri.org/IProcessor/DoProcessingResponse</a:Action> <h:CorrelationID xmlns:h="http://tempuri.org/">1234</h:CorrelationID> <a:RelatesTo u:Id="_4">uuid:40f800a0-9613-4f4a-96c5-b9fd98085deb</a:RelatesTo> <o:Security s:mustUnderstand="1" xmlns:o="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"> <!-- WS-Security header stuff --> </o:Security> </s:Header> <s:Body u:Id="_1"> <e:EncryptedData Id="_2" Type="http://www.w3.org/2001/04/xmlenc#Content" xmlns:e="http://www.w3.org/2001/04/xmlenc#"> <e:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/> <e:CipherData> <e:CipherValue>NfA6XunmyLlT2ucA+5QneoawHm+imcaCltDAJC1mRZOSxoB6YGpDLY1FyVykPbPGDoFGUESLsmvvbD62sNnRrgE+AuKPo+1CD3DF4LfurRcEv9A50ba9V+ViqlrhydhK</e:CipherValue> </e:CipherData> </e:EncryptedData> </s:Body> </s:Envelope> This response uses simple one-character namespace prefixes for most things, such as 's' for SOAP Envelope, 'a' for WS-Addressing, 'o' for 'WS-Security', etc. The Java client, namely WSS4J, seems to expect the following: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://www.w3.org/2005/08/addressing" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"> <soap:Header> <wsa:Action soap:mustUnderstand="1" wsu:Id="_3">http://tempuri.org/IProcessor/DoProcessingResponse</wsa:Action> <h:CorrelationID xmlns:h="http://tempuri.org/">1234</h:CorrelationID> <wsa:RelatesTo wsu:Id="_4">uuid:40f800a0-9613-4f4a-96c5-b9fd98085deb</a:RelatesTo> <wsse:Security soap:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"> <!-- WS-Security header stuff --> </wsse:Security> </soap:Header> <soap:Body u:Id="_1"> <xenc:EncryptedData Id="_2" Type="http://www.w3.org/2001/04/xmlenc#Content" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"> <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/> <xenc:CipherData> <xenc:CipherValue>NfA6XunmyLlT2ucA+5QneoawHm+imcaCltDAJC1mRZOSxoB6YGpDLY1FyVykPbPGDoFGUESLsmvvbD62sNnRrgE+AuKPo+1CD3DF4LfurRcEv9A50ba9V+ViqlrhydhK</xenc:CipherValue> </xenc:CipherData> </xenc:EncryptedData> </soap:Body> </soap:Envelope> Upon receipt of my response message, the Java client and WSS4J seem to want to look up elements by their own internal xml aliases, such as 'wsa' for WS-Addressing, and 'wsse' for WS-Security Extensions. Since neither of those namespaces are present in the actual response xml, exceptions are thrown. I am wondering if there is any simple way to transform an xml document from one set of namespaces to another set using C#, .NET, and the System.Xml namespace. I've poked around with XmlNamespaceManager a bit, but it does not seem to fully support what I need...or at least, I have been unable to find any really useful examples, and am not fully sure how it works. I am trying to avoid having to write some heavy-duty process to handle this manually myself, as I do not want to drastically impact the performance of our services when called by a Java Axis/WSS4J client.

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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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  • 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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  • Get graphics information from font file. How to develop font parser similar to PDFView's font parser

    - by HBA
    Hi, I am trying to convert text into graphics using c#. My input is character string and output is bitmap with the input text. After lot of search I found some ways to do it, I found some techiques which uses this kind of techinque. For Example While creating Captcha, we have to print the character in the bitmap. But for that I should have the font installed in my windows. I can not perform such operation without installing the font. I have .ttf file with me but I dont want to install it because my work for that font is temporary only. Is there any way where I can extract out the Font's graphical information by providing the Character? I have also found font parser code http://swinglabs.java.sun.com/hudson/job/PDFRenderer%20Weekly%20Build/javadoc/com/sun/pdfview/font/package-summary.html Can anyone please provide me how to develpo similar thing using c#.Net? Or From where can I get the algorithm to parce font?

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  • Real average filesize in a set of files...

    - by JD
    Hi, I have an apparently "simple" problem but I can't find the solution for some reason... I have n millions files of different sizes and I want to find the average filesize. To simplify it, I grouped them in multiples of 16KB. < 16 KB = 18689546 files < 32 KB = 1365713 files < 48 KB = 1168186 files ... Of course, the simple (total_size / number of files) does not work. It gives an average of 291KB... What would be the algorithm to calculate the real average...? Thx, JD

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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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  • Is it possible to use Regex through Hexadecimal to find email addresses

    - by LukeJenx
    Not sure if this is even possible but I have been looking at using Regex to get an email address that is in Hex. Basically this is to build up some of my automated forensic tools but I am having problems on making a suitable Regex algorithm. Regex for email: /^([a-z0-9_.-]+)@([\da-z.-]+).([a-z.]{2,6})$/ Hex values: @ = 40 . = 2E .com = 636f6d _ = 5f A/a = 41/61 [1] Z/z = 5a/7a - = 2d This is what I have got at the moment (it only takes into account lower case and .com). But it doesn't work! Have I messed something simple up? "/^([61-7a]+)40([61-7a]+)23(636f6d)$/" [1] I know email can only be lower case but I need to take uppercase into account too.

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