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  • C++ Numerical truncation error

    - by Andrew
    Hello everyone, sorry if dumb but could not find an answer. #include <iostream> using namespace std; int main() { double a(0); double b(0.001); cout << a - 0.0 << endl; for (;a<1.0;a+=b); cout << a - 1.0 << endl; for (;a<10.0;a+=b); cout << a - 10.0 << endl; cout << a - 10.0-b << endl; return 0; } Output: 0 6.66134e-16 0.001 -1.03583e-13 Tried compiling it with MSVC9, MSVC10, Borland C++ 2010. All of them arrive in the end to the error of about 1e-13. Is it normal to have such a significant error accumulation over only a 1000, 10000 increments?

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  • How to put 1000 lightweight server applications in the cloud

    - by Dan Bird
    The company I work for sells a commercial desktop/server app that runs on any non dedicated Windows PC or server and uses Tomcat for all interactions with the application. Customers are asking that we host their instance of the application so they don't have to run it locally on their own servers. The app is lightweight and an average server, in theory, could handle 25-50 instances before users would notice a slowdown. However only 1 instance can run per Windows instance (because the application writes to a common registry branch) so we'd need something like VMWare to create 25-50 Windows instances. We know we eventually need to reprogram to make it truly cloud-worthy but what would you recommend for a server farm or whatever for this? We don't have the setup to purchase our own servers so we must use a 3rd party. We have budgeted $500 - $1000 per year per customer for this service. Thanks in advance for your suggestions, experiences and guidance.

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  • Expanding Git SHA1 information into a checkin without archiving?

    - by Tim Lin
    Is there a way to include git commit hashes inside a file everytime I commit? I can only find out how to do this during archiving but I haven't been able to find out how to do this for every commit. I'm doing scientific programming with git as revision control, so this kind of functionality would be very helpful for reproducibility reasons (i.e., have the git hash automatically included in all result files and figures).

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  • For distributed applications, which to use, ASIO vs. MPI?

    - by Rhubarb
    I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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  • Whats the difference between Paxos and W+R>=N in Cassandra?

    - by user1128016
    Dynamo-like databases (e.g. Cassandra) provide ability to enforce consistency by means of quorum, i.e. a number of synchronously written replicas (W) and a number of replicas to read (R) should be chosen in such a way that W+RN where N is a replication factor. On the other hand, PAXOS-based systems like Zookeeper are also used as a consistent fault-tolerant storage. What is the difference between these two approaches? Does PAXOS provide guarantees that are not provided by W+RN schema?

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  • What should i do for accomodating large scale data storage and retrieval?

    - by kailashbuki
    There's two columns in the table inside mysql database. First column contains the fingerprint while the second one contains the list of documents which have that fingerprint. It's much like an inverted index built by search engines. An instance of a record inside the table is shown below; 34 "doc1, doc2, doc45" The number of fingerprints is very large(can range up to trillions). There are basically following operations in the database: inserting/updating the record & retrieving the record accoring to the match in fingerprint. The table definition python snippet is: self.cursor.execute("CREATE TABLE IF NOT EXISTS `fingerprint` (fp BIGINT, documents TEXT)") And the snippet for insert/update operation is: if self.cursor.execute("UPDATE `fingerprint` SET documents=CONCAT(documents,%s) WHERE fp=%s",(","+newDocId, thisFP))== 0L: self.cursor.execute("INSERT INTO `fingerprint` VALUES (%s, %s)", (thisFP,newDocId)) The only bottleneck i have observed so far is the query time in mysql. My whole application is web based. So time is a critical factor. I have also thought of using cassandra but have less knowledge of it. Please suggest me a better way to tackle this problem.

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  • Are batch mutations atomic in Cassandra?

    - by user317459
    The Cassandra API supports batch mutations: batch_mutate(keyspace, mutation_map, consistency_level): Executes the specified mutations on the keyspace. mutation_map is a map; the outer map maps the key to the inner map, which maps the column family to the Mutation; can be read as: map. To be more specific, the outer map key is a row key, the inner map key is the column family name. A Mutation specifies either columns to insert or columns to delete. See Mutation and Deletion above for more details. Are all mutations that are executed in a batch executed atomically? So if one of the mutations fails, do the others fail too?

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  • SDCC and malloc() - allocating much less memory than is available

    - by Duncan Bayne
    When I run compile this code with SDCC 3.1.0, and run it on an Amstrad CPC 464 (under emulation, with WinCPC 0.9.26 running on Wine): void _test_malloc() { long idx = 0; while (1) { if (malloc(5)) { printf("%ld\r\n", ++idx); } else { printf("done"); break; } } } ... it consistently taps out at 92 malloc()s. I make that 460 bytes, which leads me to a couple of questions: What is malloc() doing on this system? I was sort of hoping for an order of magnitude more storage even on a 64kB system The behaviour is consistent on 64kB systems and 128kB systems; do I have to perform some sort of magic to access the additional memory, like manual bank switching?

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  • Preallocate memory for a program in Linux before it gets started

    - by Fyg
    Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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  • Recommendations for Open Source Parallel programming IDE

    - by Andrew Bolster
    What are the best IDE's / IDE plugins / Tools, etc for programming with CUDA / MPI etc? I've been working in these frameworks for a short while but feel like the IDE could be doing more heavy lifting in terms of scaling and job processing interactions. (I usually use Eclipse or Netbeans, and usually in C/C++ with occasional Java, and its a vague question but I can't think of any more specific way to put it)

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  • What are the advantages / disadvantages of a Cloud-based / Web-based IDE?

    - by Gabe
    I'm writing this as DevConnections in Las Vegas is happening. Visual Studio 2010 has been released and I now have this 3GB beast installed to my machine. (I'll admit, it has some nice features.) However, while the install was monopolizing my computer's resources I began to wish that my IDE worked more like Google Documents (instantly available, available anywhere, easy to share, easy to collaborate, naturally versioned). A few Google (and StackOverflow) searches led me to : Coderun Bespin I'm well aware that these IDE's are missing a lot of what exists in VS 2010. However, that isn't my question. Instead, I'm wondering what benefits a web-based IDE might have? Assuming a company invests the time to create the missing features, what is the downside?

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  • Efficiency of manually written loops vs operator overloads (C++)

    - by Sagekilla
    Hi all, in the program I'm working on I have 3-element arrays, which I use as mathematical vectors for all intents and purposes. Through the course of writing my code, I was tempted to just roll my own Vector class with simple +, -, *, /, etc overloads so I can simplify statements like: for (int i = 0; i < 3; i++) r[i] = r1[i] - r2[i]; // becomes: r = r1 - r2; Which should be more or less identical in generated code. But when it comes to more complicated things, could this really impact my performance heavily? One example that I have in my code is this: Manually written version: for (int j = 0; j < 3; j++) { p.vel[j] = p.oldVel[j] + (p.oldAcc[j] + p.acc[j]) * dt2 + (p.oldJerk[j] - p.jerk[j]) * dt12; p.pos[j] = p.oldPos[j] + (p.oldVel[j] + p.vel[j]) * dt2 + (p.oldAcc[j] - p.acc[j]) * dt12; } Using a Vector class with operator overloads: p.vel = p.oldVel + (p.oldAcc + p.acc) * dt2 + (p.oldJerk - p.jerk) * dt12; p.pos = p.oldPos + (p.oldVel + p.vel) * dt2 + (p.oldAcc - p.acc) * dt12; I am compiling my code for maximum possible speed, as it's extremely important that this code runs quickly and calculates accurately. So will me relying on my Vector's for these sorts of things really affect me? For those curious, this is part of some numerical integration code which is not trivial to run in my program. Any insight would be appreciated, as would any idioms or tricks I'm unaware of.

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  • Problem with Boost::Asio for C++

    - by Martin Lauridsen
    Hi there, For my bachelors thesis, I am implementing a distributed version of an algorithm for factoring large integers (finding the prime factorisation). This has applications in e.g. security of the RSA cryptosystem. My vision is, that clients (linux or windows) will download an application and compute some numbers (these are independant, thus suited for parallelization). The numbers (not found very often), will be sent to a master server, to collect these numbers. Once enough numbers have been collected by the master server, it will do the rest of the computation, which cannot be easily parallelized. Anyhow, to the technicalities. I was thinking to use Boost::Asio to do a socket client/server implementation, for the clients communication with the master server. Since I want to compile for both linux and windows, I thought windows would be as good a place to start as any. So I downloaded the Boost library and compiled it, as it said on the Boost Getting Started page: bootstrap .\bjam It all compiled just fine. Then I try to compile one of the tutorial examples, client.cpp, from Asio, found (here.. edit: cant post link because of restrictions). I am using the Visual C++ compiler from Microsoft Visual Studio 2008, like this: cl /EHsc /I D:\Downloads\boost_1_42_0 client.cpp But I get this error: /out:client.exe client.obj LINK : fatal error LNK1104: cannot open file 'libboost_system-vc90-mt-s-1_42.lib' Anyone have any idea what could be wrong, or how I could move forward? I have been trying pretty much all week, to get a simple client/server socket program for c++ working, but with no luck. Serious frustration kicking in. Thank you in advance.

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  • Higher speed options for executing very large (20 GB) .sql file in MySQL

    - by Jonogan
    My firm was delivered a 20+ GB .sql file in reponse to a request for data from the gov't. I don't have many options for getting the data in a different format, so I need options for how to import it in a reasonable amount of time. I'm running it on a high end server (Win 2008 64bit, MySQL 5.1) using Navicat's batch execution tool. It's been running for 14 hours and shows no signs of being near completion. Does anyone know of any higher speed options for such a transaction? Or is this what I should expect given the large file size? Thanks

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  • C++ Winsock P2P

    - by Goober
    Scenario Does anyone have any good examples of peer-to-peer (p2p) networking in C++ using Winsock? It's a requirement I have for a client who specifically needs to use this technology (god knows why). I need to determine whether this is feasible. Any help would be greatly appreciated.

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  • Cloud Apps and Single Sign-On (AD integration)

    - by Pablo Alvim
    I've been investigating some cloud vendors and the ability to implement single sign-on with them, especially when it comes to AD (Active Directory) integration. So far I've learned that with Azure this is possible through ADFS and the AppFabric Access Control offer. In AWS, since it is possible to create a VPN and see EC2 instances as a natural extension of a private datacenter, I believe implementing SSO would be rather simple (not sure if I'm right on this one... Please correct me if I'm wrong). With App Engine though, even though there is some documentation on AD synchronization (not full integration) for Google Apps, I'm struggling to find out whether AD integration would be possible... Is there any strategy for that? Any bit of information on cloud apps and AD integration will be appreciated!

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  • No recent books on MPI: is it dying?

    - by Jono
    I've never used Message Passing Interface (MPI), but I've heard its name thrown about, most recently with Windows HPC Server. I had a quick look on amazon to see if there were any books on it, but they're all dated around 7 or more years ago. Is MPI still a valid technology choice for new applications, or has it been largely superceded by other distributed programming alternatives (e.g. DataSynapse GridServer)? As it's not really an implementation, but rather a standard, what is the likelihood (assuming it's not dead) that learning it will result in better design of distributed programming systems? Is there something else I should be looking at instead?

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  • Is a Service Bus a good option to communicate with multiple external servers?

    - by PFreitas
    We are developing an application that communicates, via web services or TCP/IP sockets, with multiple servers (up to 50 different external companies). Basically, the exchanged messages are the same (XML), but depending on the inputs of our application we should call 1 or more external servers. The benefits we would expect of introducing a Service Bus in the architecture would be: 1- Remove the need to manage all point-to-point configurations (all the 50 endpoints); 2- Simplify the communication layer of our application by having only one server to talk to; Is a Service Bus a good architectural option for this scenario? What is the best (simplest) Service Bus for this kind of communication? I read a few MSDN articles on Azure Service Bus Relay, but it didn’t seem to fit our needs. Am I wrong? Thanks for your help.

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  • Parallelizing a serial algorithm

    - by user643813
    Hej folks, I am working on porting a Text mining/Natural language application from single-core to a Map-Reduce style system. One of the steps involves a while loop similar to this: Queue<Element>; while (!queue.empty()) { Element e = queue.next(); Set<Element> result = calculateResultSet(e); if (!result.empty()) { queue.addAll(result); } } Each iteration depends on the result of the one before (kind of). There is no way of determining the number of iterations this loop will have to perform. Is there a way of parallelizing a serial algorithm such as this one? I am trying to think of a feedback mechanism, that is able to provide its own input, but how would one go about parallelizing it? Thanks for any help/remarks

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