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• Issues in Convergence of Sequential minimal optimization for SVM

  - by Amol Joshi

  I have been working on Support Vector Machine for about 2 months now. I have coded SVM myself and for the optimization problem of SVM, I have used Sequential Minimal Optimization(SMO) by Mr. John Platt. Right now I am in the phase where I am going to grid search to find optimal C value for my dataset. ( Please find details of my project application and dataset details here http://stackoverflow.com/questions/2284059/svm-classification-minimum-number-of-input-sets-for-each-class) I have successfully checked my custom implemented SVM`s accuracy for C values ranging from 2^0 to 2^6. But now I am having some issues regarding the convergence of the SMO for C 128. Like I have tried to find the alpha values for C=128 and it is taking long time before it actually converges and successfully gives alpha values. Time taken for the SMO to converge is about 5 hours for C=100. This huge I think ( because SMO is supposed to be fast. ) though I`m getting good accuracy? I am screwed right not because I can not test the accuracy for higher values of C. I am actually displaying number of alphas changed in every pass of SMO and getting 10, 13, 8... alphas changing continuously. The KKT conditions assures convergence so what is so weird happening here? Please note that my implementation is working fine for C<=100 with good accuracy though the execution time is long. Please give me inputs on this issue. Thank You and Cheers.

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• Stack and Hash joint

  - by Alexandru

  I'm trying to write a data structure which is a combination of Stack and HashSet with fast push/pop/membership (I'm looking for constant time operations). Think of Python's OrderedDict. I tried a few things and I came up with the following code: HashInt and SetInt. I need to add some documentation to the source, but basically I use a hash with linear probing to store indices in a vector of the keys. Since linear probing always puts the last element at the end of a continuous range of already filled cells, pop() can be implemented very easy without a sophisticated remove operation. I have the following problems: the data structure consumes a lot of memory (some improvement is obvious: stackKeys is larger than needed). some operations are slower than if I have used fastutil (eg: pop(), even push() in some scenarios). I tried rewriting the classes using fastutil and trove4j, but the overall speed of my application halved. What performance improvements would you suggest for my code? What open-source library/code do you know that I can try?

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• Rotate a feature Image in Open Layers - ReApply StyleMap to layer.

  - by Ozaki

  I have an open layers map. It adds and removes my "imageFeature" every 10secs or so. I have a JSON feed that gives me the rotation that I need, I have a request to get that rotation and set it as a variable of rotationv. Everything works but the fact when the image is recreated it does not update the rotation. My code is as follows: JSON request: var rotationv = (function () { rotationv = null; $.ajax({ 'async': false, 'global': true, 'url': urldefault, 'dataType': "json", 'success': function (data) { rotationv = data.rotation; } }); return rotationv })(); Creating image feature: imageFeature = new OpenLayers.Feature.Vector( new OpenLayers.Geometry.Point(mylon, mylat), { rotation: rotationv } ); The image is set in the styling elsewhere. Why does this not rotate my image? Debugging with firebug I now notice that "rotationv" is updating as per it should be. But when the point is destroyed then added again it does not apply the new rotation... Add: I realised that the "image" is applied as per the layer. So I need to figure out how to re apply the stylemap to the layer so it will trigger the "update" on the page. //redefine layer 2 so it can be updated - test.js is just a 0.0 ref// var layer2 = new OpenLayers.Layer.GML("Layer 2", "test.js", { format: OpenLayers.Format.GeoJSON, styleMap: styleMap }); But even if I add the above into my function still no luck. Included map.addLayers([layer2]); into the function as well. Edit: Attaching stylemap: var styleMap = new OpenLayers.StyleMap({ "default": new OpenLayers.Style({ rotation: rotationv, labelXOffset: "0", labelYOffset: "-15", graphicZIndex: 1 }) });

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• Is a VCS appropriate for usage by a designer?

  - by iconiK

  I know that a VCS is absolutely critical for a developer to increase productivity and protect the code, no doubts about it. But what about a designer, using say, Photoshop (though it's not specific to any tools, just to make my point clearer). VCSs uses delta compression to store different versions of files. This works very well for code, but for images, that's a problem. Raster image files are binary formats, though vector image files are text (SVG comes to my mind) and pose to problem. The problem comes with .psd files (and any other image "source" file) - those can get pretty big and since I'm not familiar with the format, I'll consider them as binary files. How would a VCS work in this condition? The repository could be pretty darned big if the VCS server isn't able to diff the files efficiently (or worse, not at all) and over time this can become a really big pain when someone needs to check out the repository (or clone it if using a DVCS). Have any of you used a VCS for this purpose? How well does it work? I'm mostly interested in Mercurial, though this is a general situation that applies to any VCS.

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• C++: Check istream has non-space, non-tab, non-newline characters left without extracting chars

  - by KRao

  I am reading a std::istream and I need to verify without extracting characters that: 1) The stream is not "empty", i.e. that trying to read a char will not result in an fail state (solved by using peek() member function and checking fail state, then setting back to original state) 2) That among the characters left there is at least one which is not a space, a tab or a newline char. The reason for this is, is that I am reading text files containing say one int per line, and sometimes there may be extra spaces / new-lines at the end of the file and this causes issues when I try get back the data from the file to a vector of int. A peek(int n) would probably do what I need but I am stuck with its implementation. I know I could just read istream like: while (myInt << myIstream) {...} //Will fail when I am at the end but the same check would fail for a number of different conditions (say I have something which is not an int on some line) and being able to differentiate between the two reading errors (unexpected thing, nothing left) would help me to write more robust code, as I could write: while (something_left(myIstream)) { myInt << myIstream; if (myStream.fail()) {...} //Horrible things happened } Thank you!

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• How do I best display CheckBoxes in SQL Server Reporting Services?

  - by Yadyn

  One of the many quirks of Reporting Services we've run across is the complete and utter lack of a CheckBox control or even something remotely similar. We have a form that should appear automatically filled out based on information pulled from a database. We have several bit datatype fields. Printing out "True" or "False" just looks silly, as this is supposed to look like a form that has been auto-filled out, so we want to have a series of checkboxes and labels that are either checked or unchecked. We are running SSRS 2005 but I'm not aware of SSRS 2008 having added a CheckBox control. Even if it did, we'd need to have an alternative for the time being. The best we've found so far is: use Wingdings use images use text boxes with borders and print a blank/space or a capital X All three approaches require IIF expression shenanigans. The Wingdings approach seemed to work acceptably, and was the most aesthetically pleasing except that for whatever reason it didn't always print correctly. More importantly, PDF exports, also for whatever reason, converted all fonts (generally) to Arial and so we got funky letters instead of the Windings dingbats. Images, being a pixel-based raster, don't do so well when printed along side vector stuff like text. Unless handled carefully, they tend to stretch, pixelate, and do other unprofessional looking things. While these methods do work (some with limitations as mentioned above) none of them are particularly elegant. Are we missing something obvious? Not so obvious? Does someone at Microsoft have a good reason why such a control was not provided in SSRS 2000, let alone 2 versions and 8 years later? This can't be the first time this issue has come up...

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• ai: Determining what tests to run to get most useful data

  - by Sai Emrys

  This is for http://cssfingerprint.com I have a system (see about page on site for details) where: I need to output a ranked list, with confidences, of categories that match a particular feature vector the binary feature vectors are a list of site IDs & whether this session detected a hit feature vectors are, for a given categorization, somewhat noisy (sites will decay out of history, and people will visit sites they don't normally visit) categories are a large, non-closed set (user IDs) my total feature space is approximately 50 million items (URLs) for any given test, I can only query approx. 0.2% of that space I can only make the decision of what to query, based on results so far, ~10-30 times, and must do so in <~100ms (though I can take much longer to do post-processing, relevant aggregation, etc) getting the AI's probability ranking of categories based on results so far is mildly expensive; ideally the decision will depend mostly on a few cheap sql queries I have training data that can say authoritatively that any two feature vectors are the same category but not that they are different (people sometimes forget their codes and use new ones, thereby making a new user id) I need an algorithm to determine what features (sites) are most likely to have a high ROI to query (i.e. to better discriminate between plausible-so-far categories [users], and to increase certainty that it's any given one). This needs to take into balance exploitation (test based on prior test data) and exploration (test stuff that's not been tested enough to find out how it performs). There's another question that deals with a priori ranking; this one is specifically about a posteriori ranking based on results gathered so far. Right now, I have little enough data that I can just always test everything that anyone else has ever gotten a hit for, but eventually that won't be the case, at which point this problem will need to be solved. I imagine that this is a fairly standard problem in AI - having a cheap heuristic for what expensive queries to make - but it wasn't covered in my AI class, so I don't actually know whether there's a standard answer. So, relevant reading that's not too math-heavy would be helpful, as well as suggestions for particular algorithms. What's a good way to approach this problem?

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• WTK emulator bluetooth connection problem

  - by Gokhan B.

  Hi! I'm developing a J2ME program with eclipse / WTK 2.5.2 and having problem with connecting two emulators using bluetooth. There is one server and one .client running on two different emulators. The problem is client program cannot discover any bluetooth device. Here is the server and client codes: public Server() { try { LocalDevice local = LocalDevice.getLocalDevice(); local.setDiscoverable(DiscoveryAgent.GIAC); server = (StreamConnectionNotifier) Connector.open("btspp://localhost:" + UUID_STRING + ";name=" + SERVICE_NAME); Util.Log("EchoServer() Server connector open!"); } catch (Exception e) {} } after calling Connector.open, I get following warning in console, which i believe is related: Warning: Unregistered device: unspecified and client code that searches for devices: public SearchForDevices(String uuid, String nm) { UUIDStr = uuid; srchServiceName = nm; try { LocalDevice local = LocalDevice.getLocalDevice(); agent = local.getDiscoveryAgent(); deviceList = new Vector(); agent.startInquiry(DiscoveryAgent.GIAC, this); // non-blocking } catch (Exception e) {} } system never calls deviceDiscovered, but calls inquiryCompleted() with INQUIRY_COMPLETED paramter, so I suppose client program runs fine. Bluetooth is enabled at emulator settings.. any ideas ?

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• Certain transformations in Open Inventor(Coin3D)

  - by Marc

  Hi, I am quite new to Open Inventor(Coin3D) and have the following problem: I have a SoSelection holding a root node(also SoSeparator). And the root node holds a number of SoSeparator nodes. Each of these SoSeparator nodes holds a SoTransform node and a SoCube node. When I select one cube node I want all other cubes within a certain distance to the selected cube to arrange in a circle arround the selected cube. (Moreover all of the cubes should be on a plane than) An additional information: My cubes are always oriented in the camera direction with (cubeTransform_-rotation.connectFrom(&camera_-orientation) Assuming the selected cube is the center of the circle, how do I translate the other cubes in a circle on a plane(perpendicular to the vector between the selected cube and the camera)? Especially how do I find coordinates on the plain on which the circle should be which have a certain distance from the Axis (from center cube to camera). What I already did is to search for the for all cubes within a certain distance as soon as one cube is selected. As a result I already have the required separators (which are holding the according SoTransforms and SoCubes) in a SoPathList. Now I want to arrange the cubes by modifing the according SoTransform-translation values. Regards Mark

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• iphone encryption not working

  - by Futur

  I have this encryption/decryption implemented and executes with no error, but i am unable to decrypt the data and im not sure whether the data is encrypted, kindly help. - (NSData *)AES256EncryptWithKey:(NSString *)key { char keyPtr[kCCKeySizeAES256+1]; bzero(keyPtr, sizeof(keyPtr)); [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding]; NSUInteger dataLength = [strData length]; data = [[NSData alloc] init]; data = [strData dataUsingEncoding:NSUTF8StringEncoding]; size_t bufferSize = dataLength + kCCBlockSizeAES128; void *pribuffer = malloc(bufferSize); size_t numBytesEncrypted = 0; CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, NULL /* initialization vector (optional) */, [data bytes], dataLength, /* input */ [data bytes], bufferSize, /* output */ &numBytesEncrypted); if (cryptStatus == kCCSuccess) { return [NSData dataWithBytesNoCopy:data length:numBytesEncrypted]; }} The decryption is : -(NSData *)AES256DecryptWithKey:(NSString *)key andForData:(NSData *)objDataObject { char keyPtr[kCCKeySizeAES256+1]; bzero(keyPtr, sizeof(keyPtr)); [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding]; NSUInteger dataLength = [objDataObject length]; size_t bufferSize = dataLength + kCCBlockSizeAES128; void *buffer = malloc(bufferSize); size_t numBytesDecrypted = 0; CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, NULL, [objDataObject bytes], dataLength, [objDataObject bytes], bufferSize, &numBytesDecrypted); if (cryptStatus == kCCSuccess) { return [NSData dataWithBytesNoCopy:objDataObject length:numBytesDecrypted]; } } i call the above methods like this: CryptoClass *obj = [CryptoClass new]; NSData *objData = [obj AES256EncryptWithKey:@"hell"]; NSData *val = [obj AES256DecryptWithKey:@"hell" andForData:objData ]; NSLog(@"decrypted string is : %@ AND LENGTH IS %d",[val description],[val length]); Decryption doesnt seem to happen at all and the encryption - i am not sure about it, kindly help me here.

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• Instantiating class with custom allocator in shared memory

  - by recipriversexclusion

  I'm pulling my hair due to the following problem: I am following the example given in boost.interprocess documentation to instantiate a fixed-size ring buffer buffer class that I wrote in shared memory. The skeleton constructor for my class is: template<typename ItemType, class Allocator > SharedMemoryBuffer<ItemType, Allocator>::SharedMemoryBuffer( unsigned long capacity ){ m_capacity = capacity; // Create the buffer nodes. m_start_ptr = this->allocator->allocate(); // allocate first buffer node BufferNode* ptr = m_start_ptr; for( int i = 0 ; i < this->capacity()-1; i++ ) { BufferNode* p = this->allocator->allocate(); // allocate a buffer node } } My first question: Does this sort of allocation guarantee that the buffer nodes are allocated in contiguous memory locations, i.e. when I try to access the n'th node from address m_start_ptr + n*sizeof(BufferNode) in my Read() method would it work? If not, what's a better way to keep the nodes, creating a linked list? My test harness is the following: // Define an STL compatible allocator of ints that allocates from the managed_shared_memory. // This allocator will allow placing containers in the segment typedef allocator<int, managed_shared_memory::segment_manager> ShmemAllocator; //Alias a vector that uses the previous STL-like allocator so that allocates //its values from the segment typedef SharedMemoryBuffer<int, ShmemAllocator> MyBuf; int main(int argc, char *argv[]) { shared_memory_object::remove("MySharedMemory"); //Create a new segment with given name and size managed_shared_memory segment(create_only, "MySharedMemory", 65536); //Initialize shared memory STL-compatible allocator const ShmemAllocator alloc_inst (segment.get_segment_manager()); //Construct a buffer named "MyBuffer" in shared memory with argument alloc_inst MyBuf *pBuf = segment.construct<MyBuf>("MyBuffer")(100, alloc_inst); } This gives me all kinds of compilation errors related to templates for the last statement. What am I doing wrong?

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• How can I change the precision of printing with the stl?

  - by mmr

  This might be a repeat, but my google-fu failed to find it. I want to print numbers to a file using the stl with the number of decimal places, rather than overall precision. So, if I do this: int precision = 16; std::vector<double> thePoint(3); thePoint[0] = 86.3671436; thePoint[0] = -334.8866574; thePoint[0] = 24.2814; ofstream file1(tempFileName, ios::trunc); file1 << std::setprecision(precision) << thePoint[0] << "\\" << thePoint[1] << "\\" << thePoint[2] << "\\"; I'll get numbers like this: 86.36714359999999\-334.8866574\24.28140258789063 What I want is this: 86.37\-334.89\24.28 In other words, truncating at two decimal points. If I set precision to be 4, then I'll get 86.37\-334.9\24.28 ie, the second number is improperly truncated. I do not want to have to manipulate each number explicitly to get the truncation, especially because I seem to be getting the occasional 9 repeating or 0000000001 or something like that that's left behind. I'm sure there's something obvious, like using the printf(%.2f) or something like that, but I'm unsure how to mix that with the stl << and ofstream.

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• How to implement RSA-CBC?(I have uploaded the request document)

  - by tq0fqeu

  I don't konw more about cipher, I just want to implement RSA-CBC which maybe mean that the result of RSA encrypt in CBC mode, and I have implemented RSA. any code languages will be ok, java will be appreciated thx I copy the request as follow(maybe has spelling wrong), but that's French I don't konw that: Pr´esentation du mini-projet Le but du mini-projet est d’impl´ementer une version ´el´ementaire du chi?rement d’un bloc par RSA et d’inclure cette primitive dans un systeme de chi?rement par bloc avec chaˆinage de blocs et IV (Initial Vector ) al´eatoire. Dans ce systeme, un texte clair (`a chi?rer) est d´ecompos´e en blocs de taille t (?x´ee par l’utilisa- teur), chaque bloc (clair) est chi?r´e par RSA en un bloc crypt´e de mˆeme taille, puis le cryptogramme associ´e au texte clair initial est obtenu en chaˆinant les blocs crypt´es par la m´ethode CBC (cipher- block chaining) d´ecrite dans le cours (voir poly “Block Ciphers”) Votre programme devra demander a l’utilisateur la taille t, puis, apres g´en´eration des cl´es publique et priv´ee, lui proposer de chi?rer ou d´echi?rer un (court) ?chier ASCII. Il est indispensable que votre programme soit au moins capable de traiter le cas (tres peu r´ealiste du point de vue de la s´ecurit´e) t = 32. Pour les traiter des blocs plus grands, il vous faudra impl´ementer des routines d’arithm´etique multi-pr´ecision ; pour cela, je vous conseille de faire appela des bibliotheques libres comme GMP (GNU Multiprecision Library). Pour la g´en´eration al´eatoire des nombres premiers p et q, vous pouvez ´egalement faire appela des bibliotheques sp´ecialis´ees,a condition de me donner toutes les pr´ecisions n´ecessaires. Vous devez m’envoyer (avant une date qui reste a ?xer)a mon adresse ´electronique ([email protected]) un courriel (sujet : [MI1-crypto] : devoir, corps du message : les noms des ´etudiants ayant travaill´e sur le mini-projet) auquel sera attach´e un dossier compress´e regroupant vos sources C ou Java comment´ees, votre programme ex´ecutable, et un ?chier texte ou PDF donnant toutes les pr´ecisions sur les biblioth`eques utilis´ees, vos choix algorithmiques et d’impl´ementation, et les raisons de ces choix (complexit´e algorithmique, robus- tesse, facilit´e d’impl´ementation, etc.). Vous pouvez travailler en binˆome ou en trinˆome, mais je serai nettement plus exigeant avec les trinˆomes I have uploaded the request at http://uploading.com/files/22emmm6b/enonce_projet.pdf/ thx

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• LocalAlloc and LocalRealloc usage

  - by PaulH

  I have a Visual Studio 2008 C++ Windows Mobile 6 application where I'm using a FindFirst() / FindNext() style API to get a collection of items. I do not know how many items will be in the list ahead of time. So, I would like to dynamically allocate an array for these items. Normally, I would use a std::vector<>, but, for other reasons, that's not an option for this application. So, I'm using LocalAlloc() and LocalReAlloc(). What I'm not clear on is if this memory should be marked fixed or moveable. The application runs fine either way. I'm just wondering what's 'correct'. int count = 0; INFO_STRUCT* info = ( INFO_STRUCT* )LocalAlloc( LHND, sizeof( INFO_STRUCT ) ); while( S_OK == GetInfo( &info[ count ] ) { ++count; info = ( INFO_STRUCT* )LocalRealloc( info, sizeof( INFO_STRUCT ) * ( count + 1 ), LHND ); } if( count > 0 ) { // use the data in some interesting way... } LocalFree( info ); Thanks, PaulH

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• How does real-time collaboration with multiple clients work in a system using operation transformati

  - by Saikat Chakrabarti

  I just finished reading High-Latency, Low-Bandwidth Windowing in the Jupiter Collaboration System and I mostly followed everything until part 6: global consistency. This part describes how the system described in the paper can be extended to accomodate for multiple clients connected to the server. However, the explanation is very short and essentially says the system will work if the central server merely forwards client messages to all the other clients. I don't really understand how this works though. What state vector would be sent in the message that is sent to all the other clients? Does the server maintain separate state vectors for each client? Does it maintain a separate copy of the widgets locally for each client? The simple example I can think of is this setup: imagine client A, server, and client B with client A and client B both connected to the server. To start, all three have the state object "ABCD". Then, client A sends the message "insert character F at position 0" at the same time client B sends the message "insert character G at position 0" to the server. It seems like simply relaying client A's message to client B and vice versa doesn't actually handle this case. So what exactly does the server do?

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• 1D Function into 2D Function Interpolation

  - by Drazick

  Hello. I have a 1D function which I want to interpolate into 2D function. I know the function should have "Polar Symmetry". Hence I use the following code (Matlab Syntax): Assuming the 1D function is LSF of the length 15. [x, y] = meshgrid([-7:7]); r = sqrt(x.^2 + y.^2); PSF = interp1([-7:7], LSF, r(:)); % Sometimes using 'spline' option, same results. PSF = reshape(PSF, [7, 7]); I have few problems: 1. Got some overshoot at the edges (As there some Extrapolation). 2. Can't enforce some assumptions (Monotonic, Non Negative). Is there a better Interpolation method for those circumstances? I couldn't find "Lanczos" based interpolation I can use the same way as interp1 (For a certain vector of points, in "imresize" you can only set the length). Is there such function anywhere? Has anyone encountered a function which allows enforcing some assumptions (Monotonically Decreasing, Non Negative, etc..). Thanks.

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• If I wanted to make a Pac-Man Game?

  - by SoulBeaver

  I am immediately placing this as a community wiki thing. I don't want to ask for help in programming yet or have even a specific question about programming, but rather the process and the resources needed to make such a game. To put it simply: My college friend and I decided to give ourselves a really big challenge to further our skills in programming. In six months time we want to show ourselves a Pac-Man game. Pac-Man will be AI-controlled like the Ghosts and whichever Pac-Man lives the longest after a set of tries wins. This isn't like anything we've done so far. The goal here, for me, isn't to create a perfect game, but to try and complete it, learn a whole bunch in the process. Even if I don't finish in the time, which is a good possibility, I would want to have at least tried this. So my question is this: How should I start preparing myself? I already have started vector math, matrices, all that fun stuff. My desired platform would be DirectX 9.0c; is that advisable? Keep in mind that this is not a preference just for this project, but I wish to have some kind of future in graphics develepment, so I want to pick a platform that is future-safe. As for the game development in general, what should I take into consideration? I have never done a real game before, so any and all advise to development of mid-scale projects( if this would be a mid-scale project ) is greatly appreciated. My main concerns are the pit-falls and demotivators. Sorry if the question is so vague. If it doesn't belong here, then I will remove it. Otherwise, any and all advise regarding making larger projects is greatly appreciated.

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• Efficient alternative to merge() when building dataframe from json files with R?

  - by Bryan

  I have written the following code which works, but is painfully slow once I start executing it over thousands of records: require("RJSONIO") people_data <- data.frame(person_id=numeric(0)) json_data <- fromJSON(json_file) n_people <- length(json_data) for(lender in 1:n_people) { person_dataframe <- as.data.frame(t(unlist(json_data[[person]]))) people_data <- merge(people_data, person_dataframe, all=TRUE) } output_file <- paste("people_data",".csv") write.csv(people_data, file=output_file) I am attempting to build a unified data table from a series of json-formated files. The fromJSON() function reads in the data as lists of lists. Each element of the list is a person, which then contains a list of the attributes for that person. For example: [[1]] person_id name gender hair_color [[2]] person_id name location gender height [[...]] structure(list(person_id = "Amy123", name = "Amy", gender = "F", hair_color = "brown"), .Names = c("person_id", "name", "gender", "hair_color")) structure(list(person_id = "matt53", name = "Matt", location = structure(c(47231, "IN"), .Names = c("zip_code", "state")), gender = "M", height = 172), .Names = c("person_id", "name", "location", "gender", "height")) The end result of the code above is matrix where the columns are every person-attribute that appears in the structure above, and the rows are the relevant values for each person. As you can see though, some data is missing for some of the people, so I need to ensure those show up as NA and make sure things end up in the right columns. Further, location itself is a vector with two components: state and zip_code, meaning it needs to be flattened to location.state and location.zip_code before it can be merged with another person record; this is what I use unlist() for. I then keep the running master table in people_data. The above code works, but do you know of a more efficient way to accomplish what I'm trying to do? It appears the merge() is slowing this to a crawl... I have hundreds of files with hundreds of people in each file. Thanks! Bryan

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• shared memory STL maps

  - by user306963

  Hello, I am writing an Apache module in C++. I need to store the common data that all childs need to read as a portion of shared memory. Structure is kind of map of vectors, so I want to use STL map and vectors for it. I have written a shared allocator and a shared manager for the purpose, they work fine for vectors but not for maps, below is the example: typedef vector<CustomersData, SharedAllocator<CustomersData> > CustomerVector; CustomerVector spData; //this one works fine typedef SharedAllocator< pair< const int, CustomerVector > > PairAllocator; typedef map< int, CustomerVector, less<int>, PairAllocator > SharedMap; SharedMap spIndex; //this one doesn't work I get compile time errors when I try to use the second object (spIndex), which are someting like: ../SpatialIndex.h:97: error: '((SpatialIndex*)this)-SpatialIndex::spIndex' does not have class type It looks like the compiler cannot determine a type for SharedMap template type, which is strange in my opinion, it seems to me that all the template parameters have been specified. Can you help? Thanks Benvenuto

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• What would be the safest way to store objects of classes derived from a common interface in a common

  - by Svenstaro

  I'd like to manage a bunch of objects of classes derived from a shared interface class in a common container. To illustrate the problem, let's say I'm building a game which will contain different actors. Let's call the interface IActor and derive Enemy and Civilian from it. Now, the idea is to have my game main loop be able to do this: // somewhere during init std::vector<IActor> ActorList; Enemy EvilGuy; Civilian CoolGuy; ActorList.push_back(EvilGuy); ActorList.push_back(CoolGuy); and // main loop while(!done) { BOOST_FOREACH(IActor CurrentActor, ActorList) { CurrentActor.Update(); CurrentActor.Draw(); } } ... or something along those lines. This example obviously won't work but that is pretty much the reason I'm asking here. I'd like to know: What would be the best, safest, highest-level way to manage those objects in a common heterogeneous container? I know about a variety of approaches (Boost::Any, void*, handler class with boost::shared_ptr, Boost.Pointer Container, dynamic_cast) but I can't decide which would be the way to go here. Also I'd like to emphasize that I want to stay away as far as possible from manual memory management or nested pointers. Help much appreciated :).

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• Best practices on using URIs as parameter value in REST calls.

  - by dafmetal

  I am designing a REST API where some resources can be filtered through query parameters. In some cases, these filter values would be resources from the same REST API. This makes for longish and pretty unreadable URIs. While this is not too much of a problem in itself because the URIs are meant to be created and manipulated programmatically, it makes for some painful debugging. I was thinking of allowing shortcuts to URIs used as filter values and I wonder if this is allowed according to the REST architecture and if there are any best practices. For example: I have a resource that gets me Java classes. Then the following request would give me all Java classes: GET http://example.org/api/v1/class Suppose I want all subclasses of the Collection Java class, then I would use the following request: GET http://example.org/api/v1/class?has-supertype=http://example.org/api/v1/class/collection That request would return me Vector, ArrayList and all other subclasses of the Collection Java class. That URI is quite long though. I could already shorten it by allowing hs as an alias for has-supertype. This would give me: GET http://example.org/api/v1/class?hs=http://example.org/api/v1/class/collection Another way to allow shorter URIs would be to allow aliases for URI prefixes. For example, I could define class as an alias for the URI prefix http://example.org/api/v1/class/. Which would give me the following possibility: GET http://example.org/api/v1/class?hs=class:collection Another possibility would be to remove the class alias entirely and always prefix the parameter value with http://example.org/api/v1/class/ as this is the only thing I would support. This would turn the request for all subtypes of Collection into: GET http://example.org/api/v1/class?hs=collection Do these "simplifications" of the original request URI still conform to the principles of a REST architecture? Or did I just go off the deep end?

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• Solving problems involving more complex data structures with CUDA

  - by Nils

  So I read a bit about CUDA and GPU programming. I noticed a few things such that access to global memory is slow (therefore shared memory should be used) and that the execution path of threads in a warp should not diverge. I also looked at the (dense) matrix multiplication example, described in the programmers manual and the nbody problem. And the trick with the implementation seems to be the same: Arrange the calculation in a grid (which it already is in case of the matrix mul); then subdivide the grid into smaller tiles; fetch the tiles into shared memory and let the threads calculate as long as possible, until it needs to reload data from the global memory into shared memory. In case of the nbody problem the calculation for each body-body interaction is exactly the same (page 682): bodyBodyInteraction(float4 bi, float4 bj, float3 ai) It takes two bodies and an acceleration vectors. The body vector has four components it's position and the weight. When reading the paper, the calculation is understood easily. But what is if we have a more complex object, with a dynamic data structure? For now just assume that we have an object (similar to the body object presented in the paper) which has a list of other objects attached and the number of objects attached is different in each thread. How could I implement that without having the execution paths of the threads to diverge? I'm also looking for literature which explains how different algorithms involving more complex data structures can be effectively implemented in CUDA.

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• List of objects or parallel arrays of properties?

  - by Headcrab

  The question is, basically: what would be more preferable, both performance-wise and design-wise - to have a list of objects of a Python class or to have several lists of numerical properties? I am writing some sort of a scientific simulation which involves a rather large system of interacting particles. For simplicity, let's say we have a set of balls bouncing inside a box so each ball has a number of numerical properties, like x-y-z-coordinates, diameter, mass, velocity vector and so on. How to store the system better? Two major options I can think of are: to make a class "Ball" with those properties and some methods, then store a list of objects of the class, e. g. [b1, b2, b3, ...bn, ...], where for each bn we can access bn.x, bn.y, bn.mass and so on; to make an array of numbers for each property, then for each i-th "ball" we can access it's 'x' coordinate as xs[i], 'y' coordinate as ys[i], 'mass' as masses[i] and so on; To me it seems that the first option represents a better design. The second option looks somewhat uglier, but might be better in terms of performance, and it could be easier to use it with numpy and scipy, which I try to use as much as I can. I am still not sure if Python will be fast enough, so it may be necessary to rewrite it in C++ or something, after initial prototyping in Python. Would the choice of data representation be different for C/C++? What about a hybrid approach, e.g. Python with C++ extension?

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• How Can I Generate Equivalent Output Using the CryptoAPI and the .NET Encryption (TripleDESCryptoSer

  - by S. Butts

  I have some C#/.NET code that encrypts and decrypts data using TripleDES encryption. It sticks to the sample code provided at MSDN pretty closely. The encryption piece looks like the following: TripleDESCryptoServiceProvider _desProvider = new TripleDESCryptoServiceProvider(); //bytes for key and initialization vector //keyBytes is 24 bytes of stuff, vectorBytes is 8 bytes of stuff byte[] keyBytes; byte[] vectorBytes; FileStream fStream = File.Open(locationOfFile, FileMode.Create, FileAccess.Write); CryptoStream cStream = new CryptoStream(fStream, _desProvider.CreateEncryptor(keyBytes, vectorBytes), CryptoStreamMode.Write); BinaryWriter bWriter = new BinaryWriter(cStream); //write out encrypted data //raw data is a few bytes of binary information byte[] rawData; bWriter.Write(rawData); With encrypting and decrypting in C#, this all works like a charm. The problem is I need to write a small Win32 utility that will duplicate the encryption above. I have tried several methods using the CryptoAPI, and I simply do not get output that the .NET piece can decrypt, no matter what I do. Can someone please tell me what the equivalent C++ code is that will produce the same output? I am not certain just what methods of the CryptoAPI the .NET functions use to encrypt the data. What options are used, and what method of generating the key is used? Before someone suggests that I just write it in C# anyway, or create some common library bridge for them, those options are unfortunately off the table. It really has to work in Win32 with .NET and without using a DLL. I have some leeway in changing the C# code. I apologize in advance if this is bone-headed, as I am new to encryption.

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• ExecutorService - scaling

  - by Stanciu Alexandru-Marian

  I am trying to write a program in Java using ExecutorService and it's function invokeAll. My question is: does the invokeAll functions solve the tasks simultaneously? I mean, if i have two processors, there will be two workers in the same time? Because a can't make it to scale correct. It takes the same time to complete the problem if i give newFixedThreadPool(2) or 1. List<Future<PartialSolution>> list = new ArrayList<Future<PartialSolution>>(); Collection<Callable<PartialSolution>> tasks = new ArrayList<Callable<PartialSolution>>(); for(PartialSolution ps : wp) { tasks.add(new Map(ps, keyWords)); } list = executor.invokeAll(tasks); Map is a class that implements Callable and wp is a vector of Partial Solutions, a class that holds some informations in different times. Why doesn't it scale? What could be the problem? Thank you, Alex

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