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  • Initialize array in amortized constant time -- what is this trick called?

    - by user946850
    There is this data structure that trades performance of array access against the need to iterate over it when clearing it. You keep a generation counter with each entry, and also a global generation counter. The "clear" operation increases the generation counter. On each access, you compare local vs. global generation counters; if they differ, the value is treated as "clean". This has come up in this answer on Stack Overflow recently, but I don't remember if this trick has an official name. Does it? One use case is Dijkstra's algorithm if only a tiny subset of the nodes has to be relaxed, and if this has to be done repeatedly.

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  • What are some concise and comprehensive introductory guide to unit testing for a self-taught programmer [closed]

    - by Superbest
    I don't have much formal training in programming and I have learned most things by looking up solutions on the internet to practical problems I have. There are some areas which I think would be valuable to learn, but which ended up both being difficult to learn and easy to avoid learning for a self-taught programmer. Unit testing is one of them. Specifically, I am interested in tests in and for C#/.NET applications using Microsoft.VisualStudio.TestTools in Visual Studio 2010 and/or 2012, but I really want a good introduction to the principles so language and IDE shouldn't matter much. At this time I'm interested in relatively trivial tests for small or medium sized programs (development time of weeks or months and mostly just myself developing). I don't necessarily intend to do test-driven development (I am aware that some say unit testing alone is supposed to be for developing features in TDD, and not an assurance that there are no bugs in the software, but unit testing is often the only kind of testing for which I have resources). I have found this tutorial which I feel gave me a decent idea of what unit tests and TDD looks like, but in trying to apply these ideas to my own projects, I often get confused by questions I can't answer and don't know how to answer, such as: What parts of my application and what sorts of things aren't necessarily worth testing? How fine grained should my tests be? Should they test every method and property separately, or work with a larger scope? What is a good naming convention for test methods? (since apparently the name of the method is the only way I will be able to tell from a glance at the test results table what works in my program and what doesn't) Is it bad to have many asserts in one test method? Since apparently VS2012 reports only that "an Assert.IsTrue failed within method MyTestMethod", and if MyTestMethod has 10 Assert.IsTrue statements, it will be irritating to figure out why a test is failing. If a lot of the functionality deals with writing and reading data to/from the disk in a not-exactly trivial fashion, how do I test that? If I provide a bunch of files as input by placing them in the program's directory, do I have to copy those files to the test project's bin/Debug folder now? If my program works with a large body of data and execution takes minutes or more, should my tests have it do the whole use all of the real data, a subset of it, or simulated data? If latter, how do I decide on the subset or how to simulate? Closely related to the previous point, if a class is such that its main operation happens in a state that is arrived to by the program after some involved operations (say, a class makes calculations on data derived from a few thousands of lines of code analyzing some raw data) how do I test just that class without inevitably ending up testing that class and all the other code that brings it to that state along with it? In general, what kind of approach should I use for test initialization? (hopefully that is the correct term, I mean preparing classes for testing by filling them in with appropriate data) How do I deal with private members? Do I just suck it up and assume that "not public = shouldn't be tested"? I have seen people suggest using private accessors and reflection, but these feel like clumsy and unsuited for regular use. Are these even good ideas? Is there anything like design patterns concerning testing specifically? I guess the main themes in what I'd like to learn more about are, (1) what are the overarching principles that should be followed (or at least considered) in every testing effort and (2) what are popular rules of thumb for writing tests. For example, at one point I recall hearing from someone that if a method is longer than 200 lines, it should be refactored - not a universally correct rule, but it has been quite helpful since I'd otherwise happily put hundreds of lines in single methods and then wonder why my code is so hard to read. Similarly I've found ReSharpers suggestions on member naming style and other things to be quite helpful in keeping my codebases sane. I see many resources both online and in print that talk about testing in the context of large applications (years of work, 10s of people or more). However, because I've never worked on such large projects, this context is very unfamiliar to me and makes the material difficult to follow and relate to my real world problems. Speaking of software development in general, advice given with the assumptions of large projects isn't always straightforward to apply to my own, smaller endeavors. Summary So my question is: What are some resources to learn about unit testing, for a hobbyist, self-taught programmer without much formal training? Ideally, I'm looking for a short and simple "bible of unit testing" which I can commit to memory, and then apply systematically by repeatedly asking myself "is this test following the bible of testing closely enough?" and then amending discrepancies if it doesn't.

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  • Good analytics tools that can track visitor actions from a particular source?

    - by tnorthcutt
    Are there good tools that can track what actions a certain subset of visitors (i.e. from a particular source) do once they're on your site? As far as I know (which could be wrong), Google Analytics can't do this beyond telling you how long they stayed, bounce rate, and average number of pages. I'm looking for something that can tell me which links they clicked on, and if possible break it down per-visitor. Free solutions would be great, but I'm anticipating that this would require a paid solution.

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  • Is the Leptonica implementation of 'Modified Median Cut' not using the median at all?

    - by TheCodeJunkie
    I'm playing around a bit with image processing and decided to read up on how color quantization worked and after a bit of reading I found the Modified Median Cut Quantization algorithm. I've been reading the code of the C implementation in Leptonica library and came across something I thought was a bit odd. Now I want to stress that I am far from an expert in this area, not am I a math-head, so I am predicting that this all comes down to me not understanding all of it and not that the implementation of the algorithm is wrong at all. The algorithm states that the vbox should be split along the lagest axis and that it should be split using the following logic The largest axis is divided by locating the bin with the median pixel (by population), selecting the longer side, and dividing in the center of that side. We could have simply put the bin with the median pixel in the shorter side, but in the early stages of subdivision, this tends to put low density clusters (that are not considered in the subdivision) in the same vbox as part of a high density cluster that will outvote it in median vbox color, even with future median-based subdivisions. The algorithm used here is particularly important in early subdivisions, and 3is useful for giving visible but low population color clusters their own vbox. This has little effect on the subdivision of high density clusters, which ultimately will have roughly equal population in their vboxes. For the sake of the argument, let's assume that we have a vbox that we are in the process of splitting and that the red axis is the largest. In the Leptonica algorithm, on line 01297, the code appears to do the following Iterate over all the possible green and blue variations of the red color For each iteration it adds to the total number of pixels (population) it's found along the red axis For each red color it sum up the population of the current red and the previous ones, thus storing an accumulated value, for each red note: when I say 'red' I mean each point along the axis that is covered by the iteration, the actual color may not be red but contains a certain amount of red So for the sake of illustration, assume we have 9 "bins" along the red axis and that they have the following populations 4 8 20 16 1 9 12 8 8 After the iteration of all red bins, the partialsum array will contain the following count for the bins mentioned above 4 12 32 48 49 58 70 78 86 And total would have a value of 86 Once that's done it's time to perform the actual median cut and for the red axis this is performed on line 01346 It iterates over bins and check they accumulated sum. And here's the part that throws me of from the description of the algorithm. It looks for the first bin that has a value that is greater than total/2 Wouldn't total/2 mean that it is looking for a bin that has a value that is greater than the average value and not the median ? The median for the above bins would be 49 The use of 43 or 49 could potentially have a huge impact on how the boxes are split, even though the algorithm then proceeds by moving to the center of the larger side of where the matched value was.. Another thing that puzzles me a bit is that the paper specified that the bin with the median value should be located, but does not mention how to proceed if there are an even number of bins.. the median would be the result of (a+b)/2 and it's not guaranteed that any of the bins contains that population count. So this is what makes me thing that there are some approximations going on that are negligible because of how the split actually takes part at the center of the larger side of the selected bin. Sorry if it got a bit long winded, but I wanted to be as thoroughas I could because it's been driving me nuts for a couple of days now ;)

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  • Visual Studio 2010 HTML5

    - by Renso
    Goal: Enabling HTML5 validation and  IntelliSense for Visual Studio 2010. By default it is set to XHTML 1.1. HTML5 support only came included with SP1 of Visual Studio 2010. However since HTML5 is not an official standard as yet and some of the 30 new elements are not suported in all browsers, so only a subset of the entire HTML5 specification is supported; support for both intellisense and validation for HTML5 with SP1. How to: After installing SP1 you have to tell Visual Studio to start using the HTML5 schema. Go to Tools -> Options, and then select Text Editor -> HTML -> Validation. Select HTML5 or XHTML5 as the target schema. So start building or converting older Visual Studio projects to HTML5 and CSS3 web applications.

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  • Emacs-like keybindings system-wide?

    - by kermit666
    Is there a way to set Emacs-like keyboard shortcuts (at least the subset mentioned below) for the whole OS? This is possible in some apps such as the terminal, Emacs (go figure :) and additionally through special plugins in some other apps (Eclipse), but I got so used to C-f-ing through text and never having to jump to arrows that I'd like to be able to do this system-wide so that I can do it whenever I'm typing - e.g. searching for songs in Rhythmbox, typing stuff into the dash or the HUD, writing mails in Thunderbird or Gmail... The combos I'm most interested in are: C-f - forward C-b - backwards C-a - home C-e - end C-d - delete C-k - delete line (note for non-emacs users - C means Ctrl)

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  • Initialize array in O(1) -- how is this trick called?

    - by user946850
    There is this pattern that trades performance of array access against the need to iterate it when clearing it. You keep a generation counter with each entry, and also a global generation counter. The "clear" operation increases the generation counter. On each access, you compare local vs. global generation counters; if they differ, the array has been reset. This has come up in StackOverflow recently, but I don't remember if this trick has an official name. Does it? One use case is Dijkstra's algorithm if only a tiny subset of the nodes has to be relaxed, and if this has to be done repeatedly.

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  • Excel Prorated SUMIF

    - by Pete Michaud
    I have a worksheet with 2 columns, one is a dollar amount, and the other is a day of the month (1 through 31) that the dollar amount is due by (the dollars are income streams). So, I use the following formula to SUM all the income streams due on or before a certain day: =SUMIF(C5:C14, "<="&$B$42,B5:B14) Column C is the due day B42 is the cell in which I input the day to compare to like "15" for "total of all income due on or before the 15th" - the idea is to have a sum of all income received for the period. Column B is the dollar amount for each income stream. My question is: Some of the income streams don't have a day next to them (the day cell in column C is blank). That means that that income stream doesn't come in as a check or a chunk on a certain date, it trickles in roughly evenly through out the month. So if the amount for the income stream is $10,000 and the day is 15 in a 30 day month, then I should add $5,000 to the total. That would be something like: =SUMIF(C5:C14, "",???) So where the due date is blank, select ???. ??? isn't just the number, it's the number*(given_day/total_days_in_month). So I think what I need for an accurate total is: =SUMIF(C5:C14, "<="&$B$42,B5:B14) + SUMIF(C5:C14, "",???) But I'm not sure how to write that exactly.

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  • SSRS - Oracle DB, Passing Date parameter

    - by davidl98
    Using SSRS with an Oracle Database. I need to prompt the user when running the report to enter a date for report. What is the best way to add in the parameter in my SSRS Report. Having problem finding the right date format. under the "Report Parameter" menu, I have setup the Report Parameters using the DateTime Datatype. Keep getting this error "ORA-01843: Not a Valid Month" Thank you for your help. Select a.OPR_Name, a.OPR, a.Trans_Desc, a.Trans_Start_Date, Cast(a.S_Date as date) as S_Date, Sum(a.Duration) as T From ( Select US_F.OPR_Name, ITH_F.OPR, ITH_F.ITH_RID, ITH_F.TRANSACT, Transact.DESC_1 as Trans_Desc, To_CHAR(ITH_F.Start_Time,'DD-Mon-YY') as Trans_Start_Date, To_CHAR(ITH_F.Start_Time,'MM/DD/YYYY') as S_Date, Substr(To_CHAR(ITH_F.Start_Time,'HH24:MI'),1,6) as Start_Time, To_CHAR(ITH_F.End_Time,'DD-Mon-YY') as Trans_End_Date, Substr(To_CHAR(ITH_F.End_Time,'HH24:MI'),1,6) as End_Time, Cast(Case When To_CHAR(ITH_F.Start_Time,'DD-Mon-YY') = To_CHAR(ITH_F.End_Time,'DD-Mon-YY') Then (((To_CHAR(ITH_F.End_Time,'SSSSS') - To_CHAR(ITH_F.Start_Time,'SSSSS')) / 60))/60 Else ((86399 - (To_CHAR(ITH_F.Start_Time,'SSSSS')) + To_CHAR(ITH_F.End_Time,'SSSSS'))/60)/60 End as Decimal(3,1)) as Duration from Elite_76_W1.ITH_F Left Join Elite_76_W1.Transact on Transact.Transact = ITH_F.Transact Left Join Elite_76_W1.US_F on US_F.OPR = ITH_F.OPR Where ITH_F.TRANSACT not in ('ASN','QC','LGOT') ) a Where a.S_Date = @Event_Date Having Sum(a.Duration) < 0 Group By a.OPR_Name, a.OPR, a.Trans_Desc, a.Trans_Start_Date, a.S_Date Order by a.OPR_Name

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  • Recurrence relation solution

    - by Travis
    I'm revising past midterms for a final exam this week and am trying to make sense of a solution my professor posted for one of past exams. (You can see the original pdf here, question #6). I'm given the original recurrence relation T(m)=3T(n/2) + n and am told T(1) = 1. I'm pretty sure the solution I've been given is wrong in a few places. The solution is as follows: Let n=2^m T(2^m) = 3T(2^(m-1)) + 2^m 3T(2^(m-1)) = 3^2*T(2^(m-2)) + 2^(m-1)*3 ... 3^(m-1)T(2) = T(1) + 2*3^(m-1) I'm pretty sure this last line is incorrect and they forgot to multiply T(1) by 3^m. He then (tries to) sum the expressions: T(2^m) = 1 + (2^m + 2^(m-1)*3 + ... + 2*3(m-1)) = 1 + 2^m(1 + (3/2)^1 + (3/2)^2 + ... + (3/2)^(m-1)) = 1 + 2^m((3/2)^m-1)*(1/2) = 1 + 3^m - 2^(m-1) = 1 + n^log 3 - n/2 Thus the algorithm is big Theta of (n^log 3). I'm pretty sure that he also got the summation wrong here. By my calculations this should be as follows: T(2^m) = 2^m + 3 * 2^(m-1) + 3^2 * 2^(m-2) + ... + 3^m (3^m because 3^m*T(1) = 3^m should be added, not 1) = 2^m * ((3/2)^1 + (3/2)^2 + ... + (3/2)^m) = 2^m * sum of (3/2)^i from i=0 to m = 2^m * ((3/2)^(m+1) - 1)/(3/2 - 1) = 2^m * ((3/2)^(m+1) - 1)/(1/2) = 2^(m+1) * 3^(m+1)/2^(m+1) - 2^(m+1) = 3^(m+1) - 2 * 2^m Replacing n = 2^m, and from that m = log n T(n) = 3*3^(log n) - 2*n n is O(3^log n), thus the runtime is big Theta of (3^log n) Does this seem right? Thanks for your help!

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  • Query Optimizing Request

    - by mithilatw
    I am very sorry if this question is structured in not a very helpful manner or the question itself is not a very good one! I need to update a MSSQL table call component every 10 minutes based on information from another table call materials_progress I have nearly 60000 records in component and more than 10000 records in materials_progress I wrote an update query to do the job, but it takes longer than 4 minutes to complete execution! Here is the query : UPDATE component SET stage_id = CASE WHEN t.required_quantity <= t.total_received THEN 27 WHEN t.total_ordered < t.total_received THEN 18 ELSE 18 END FROM ( SELECT mp.job_id, mp.line_no, mp.component, l.quantity AS line_quantity, CASE WHEN mp.component_name_id = 2 THEN l.quantity*2 ELSE l.quantity END AS required_quantity, SUM(ordered) AS total_ordered, SUM(received) AS total_received , c.component_id FROM line l LEFT JOIN component c ON c.line_id = l.line_id LEFT JOIN materials_progress mp ON l.job_id = mp.job_id AND l.line_no = mp.line_no AND c.component_name_id = mp.component_name_id WHERE mp.job_id IS NOT NULL AND (mp.cancelled IS NULL OR mp.cancelled = 0) AND (mp.manual_override IS NULL OR mp.manual_override = 0) AND c.stage_id = 18 GROUP BY mp.job_id, mp.line_no, mp.component, l.quantity, mp.component_name_id, component_id ) AS t WHERE component.component_id = t.component_id I am not going to explain the scenario as it too complex.. could somebody please please tell me what makes this query this much expensive and a way to get around it? Thank you very very much in advance!!!

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  • Query on simple C++ threadpool implementation

    - by ticketman
    Stackoverflow has been a tremendous help to me and I'd to give something back to the community. I have been implementing a simple threadpool using the tinythread C++ portable thread library, using what I have learnt from Stackoverflow. I am new to thread programming, so not that comfortable with mutexes, etc. I have a question best asked after presenting the code (which runs quite well under Linux): // ThreadPool.h class ThreadPool { public: ThreadPool(); ~ThreadPool(); // Creates a pool of threads and gets them ready to be used void CreateThreads(int numOfThreads); // Assigns a job to a thread in the pool, but doesn't start the job // Each SubmitJob call will use up one thread of the pool. // This operation can only be undone by calling StartJobs and // then waiting for the jobs to complete. On completion, // new jobs may be submitted. void SubmitJob( void (*workFunc)(void *), void *workData ); // Begins execution of all the jobs in the pool. void StartJobs(); // Waits until all jobs have completed. // The wait will block the caller. // On completion, new jobs may be submitted. void WaitForJobsToComplete(); private: enum typeOfWorkEnum { e_work, e_quit }; class ThreadData { public: bool ready; // thread has been created and is ready for work bool haveWorkToDo; typeOfWorkEnum typeOfWork; // Pointer to the work function each thread has to call. void (*workFunc)(void *); // Pointer to work data void *workData; ThreadData() : ready(false), haveWorkToDo(false) { }; }; struct ThreadArgStruct { ThreadPool *threadPoolInstance; int threadId; }; // Data for each thread ThreadData *m_ThreadData; ThreadPool(ThreadPool const&); // copy ctor hidden ThreadPool& operator=(ThreadPool const&); // assign op. hidden // Static function that provides the function pointer that a thread can call // By including the ThreadPool instance in the void * parameter, // we can use it to access other data and methods in the ThreadPool instance. static void ThreadFuncWrapper(void *arg) { ThreadArgStruct *threadArg = static_cast<ThreadArgStruct *>(arg); threadArg->threadPoolInstance->ThreadFunc(threadArg->threadId); } // The function each thread calls void ThreadFunc( int threadId ); // Called by the thread pool destructor void DestroyThreadPool(); // Total number of threads available // (fixed on creation of thread pool) int m_numOfThreads; int m_NumOfThreadsDoingWork; int m_NumOfThreadsGivenJobs; // List of threads std::vector<tthread::thread *> m_ThreadList; // Condition variable to signal each thread has been created and executing tthread::mutex m_ThreadReady_mutex; tthread::condition_variable m_ThreadReady_condvar; // Condition variable to signal each thread to start work tthread::mutex m_WorkToDo_mutex; tthread::condition_variable m_WorkToDo_condvar; // Condition variable to signal the main thread that // all threads in the pool have completed their work tthread::mutex m_WorkCompleted_mutex; tthread::condition_variable m_WorkCompleted_condvar; }; cpp file: // // ThreadPool.cpp // #include "ThreadPool.h" // This is the thread function for each thread. // All threads remain in this function until // they are asked to quit, which only happens // when terminating the thread pool. void ThreadPool::ThreadFunc( int threadId ) { ThreadData *myThreadData = &m_ThreadData[threadId]; std::cout << "Hello world: Thread " << threadId << std::endl; // Signal that this thread is ready m_ThreadReady_mutex.lock(); myThreadData->ready = true; m_ThreadReady_condvar.notify_one(); // notify the main thread m_ThreadReady_mutex.unlock(); while(true) { //tthread::lock_guard<tthread::mutex> guard(m); m_WorkToDo_mutex.lock(); while(!myThreadData->haveWorkToDo) // check for work to do m_WorkToDo_condvar.wait(m_WorkToDo_mutex); // if no work, wait here myThreadData->haveWorkToDo = false; // need to do this before unlocking the mutex m_WorkToDo_mutex.unlock(); // Do the work switch(myThreadData->typeOfWork) { case e_work: std::cout << "Thread " << threadId << ": Woken with work to do\n"; // Do work myThreadData->workFunc(myThreadData->workData); std::cout << "#Thread " << threadId << ": Work is completed\n"; break; case e_quit: std::cout << "Thread " << threadId << ": Asked to quit\n"; return; // ends the thread } // Now to signal the main thread that my work is completed m_WorkCompleted_mutex.lock(); m_NumOfThreadsDoingWork--; // Unsure if this 'if' would make the program more efficient // if(NumOfThreadsDoingWork == 0) m_WorkCompleted_condvar.notify_one(); // notify the main thread m_WorkCompleted_mutex.unlock(); } } ThreadPool::ThreadPool() { m_numOfThreads = 0; m_NumOfThreadsDoingWork = 0; m_NumOfThreadsGivenJobs = 0; } ThreadPool::~ThreadPool() { if(m_numOfThreads) { DestroyThreadPool(); delete [] m_ThreadData; } } void ThreadPool::CreateThreads(int numOfThreads) { // Check a thread pool has already been created if(m_numOfThreads > 0) return; m_NumOfThreadsGivenJobs = 0; m_NumOfThreadsDoingWork = 0; m_numOfThreads = numOfThreads; m_ThreadData = new ThreadData[m_numOfThreads]; ThreadArgStruct threadArg; for(int i=0; i<m_numOfThreads; ++i) { threadArg.threadId = i; threadArg.threadPoolInstance = this; // Creates the thread and save in a list so we can destroy it later m_ThreadList.push_back( new tthread::thread( ThreadFuncWrapper, (void *)&threadArg ) ); // It takes a little time for a thread to get established. // Best wait until it gets established before creating the next thread. m_ThreadReady_mutex.lock(); while(!m_ThreadData[i].ready) // Check if thread is ready m_ThreadReady_condvar.wait(m_ThreadReady_mutex); // If not, wait here m_ThreadReady_mutex.unlock(); } } // Adds a job to the batch, but doesn't start the job void ThreadPool::SubmitJob(void (*workFunc)(void *), void *workData) { // Check that the thread pool has been created if(!m_numOfThreads) return; if(m_NumOfThreadsGivenJobs >= m_numOfThreads) return; m_ThreadData[m_NumOfThreadsGivenJobs].workFunc = workFunc; m_ThreadData[m_NumOfThreadsGivenJobs].workData = workData; std::cout << "Submitted job " << m_NumOfThreadsGivenJobs << std::endl; m_NumOfThreadsGivenJobs++; } void ThreadPool::StartJobs() { // Check that the thread pool has been created // and some jobs have been assigned if(!m_numOfThreads || !m_NumOfThreadsGivenJobs) return; // Set 'haveworkToDo' flag for all threads m_WorkToDo_mutex.lock(); for(int i=0; i<m_NumOfThreadsGivenJobs; ++i) m_ThreadData[i].haveWorkToDo = true; m_NumOfThreadsDoingWork = m_NumOfThreadsGivenJobs; // Reset this counter so we can resubmit jobs later m_NumOfThreadsGivenJobs = 0; // Notify all threads they have work to do m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); } void ThreadPool::WaitForJobsToComplete() { // Check that a thread pool has been created if(!m_numOfThreads) return; m_WorkCompleted_mutex.lock(); while(m_NumOfThreadsDoingWork > 0) // Check if all threads have completed their work m_WorkCompleted_condvar.wait(m_WorkCompleted_mutex); // If not, wait here m_WorkCompleted_mutex.unlock(); } void ThreadPool::DestroyThreadPool() { std::cout << "Ask threads to quit\n"; m_WorkToDo_mutex.lock(); for(int i=0; i<m_numOfThreads; ++i) { m_ThreadData[i].haveWorkToDo = true; m_ThreadData[i].typeOfWork = e_quit; } m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); // As each thread terminates, catch them here for(int i=0; i<m_numOfThreads; ++i) { tthread::thread *t = m_ThreadList[i]; // Wait for thread to complete t->join(); } m_numOfThreads = 0; } Example of usage: (this calculates pi-squared/6) struct CalculationDataStruct { int inputVal; double outputVal; }; void LongCalculation( void *theSums ) { CalculationDataStruct *sums = (CalculationDataStruct *)theSums; int terms = sums->inputVal; double sum; for(int i=1; i<terms; i++) sum += 1.0/( double(i)*double(i) ); sums->outputVal = sum; } int main(int argc, char** argv) { int numThreads = 10; // Create pool ThreadPool threadPool; threadPool.CreateThreads(numThreads); // Create thread workspace CalculationDataStruct sums[numThreads]; // Set up jobs for(int i=0; i<numThreads; i++) { sums[i].inputVal = 3000*(i+1); threadPool.SubmitJob(LongCalculation, &sums[i]); } // Run the jobs threadPool.StartJobs(); threadPool.WaitForJobsToComplete(); // Print results for(int i=0; i<numThreads; i++) std::cout << "Sum of " << sums[i].inputVal << " terms is " << sums[i].outputVal << std::endl; return 0; } Question: In the ThreadPool::ThreadFunc method, would better performance be obtained if the following if statement if(NumOfThreadsDoingWork == 0) was included? Also, I'd be grateful of criticisms and ways to improve the code. At the same time, I hope the code is of use to others.

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  • LinqToSql - ChangeConflictException. when submiting child and parent

    - by ari
    This problem drives me crazy. Here's the code using (BizNetDB db = new BizNetDB()) { var dbServiceCall = db.ServiceCalls.SingleOrDefault(x => x.ServiceCallID == serviceCallDetail.ServiceCallID); var dbServiceCallDetail = dbServiceCall.ServiceCallDetaills.SingleOrDefault(x=> x.ServiceCallDetailID == serviceCallDetail.ServiceCallDetailID); if (dbServiceCallDetail == null) { dbServiceCallDetail = new Data.ServiceCallDetaill(); dbServiceCall.ServiceCallDetaills.Add(dbServiceCallDetail); } dbServiceCallDetail.EndSession = serviceCallDetail.EndSession; dbServiceCallDetail.ExitTime = serviceCallDetail.ExitTime; dbServiceCallDetail.Solution = serviceCallDetail.Solution; dbServiceCallDetail.StartSession = serviceCallDetail.StartSession; serviceCallDetail.SessionMinutes = (serviceCallDetail.EndSession - serviceCallDetail.StartSession).Minutes; serviceCallDetail.DriveMinutes = serviceCallDetail.ExitTime.HasValue ? (serviceCallDetail.StartSession - serviceCallDetail.ExitTime.Value).Minutes : 0; var totalMinutes = (from d in db.ServiceCallDetaills .Where(x => x.ServiceCallID == serviceCallDetail.ServiceCallID && x.ServiceCallDetailID != dbServiceCallDetail.ServiceCallDetailID) group d by d.ServiceCallID into g select new { SessionMinutes = g.Sum(x => x.SessionMinutes), DriveMinutes = g.Sum(x => x.DriveMinutes) }).First(); dbServiceCall.SessionMinutes = totalMinutes.SessionMinutes + serviceCallDetail.SessionMinutes; dbServiceCall.DriveMinutes = totalMinutes.DriveMinutes + serviceCallDetail.DriveMinutes; try { db.SubmitChanges(); } catch (ChangeConflictException ex) { db.ChangeConflicts.ResolveAll(RefreshMode.OverwriteCurrentValues); db.SubmitChanges(); } The second Submit did solve the problem.. but I want to solve it from the root! when I disabled this lines (The parent changes): dbServiceCall.SessionMinutes = totalMinutes.SessionMinutes + serviceCallDetail.SessionMinutes; dbServiceCall.DriveMinutes = totalMinutes.DriveMinutes + serviceCallDetail.DriveMinutes; everithing is Ok. please help...

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  • review of a codility test - pair_sum_even_count

    - by geoaxis
    I recently took an online test on codility as part of a recruitment process. I was given two simple problems to solve in 1 hour. For those who don't know codility, its an online coding test site where you can solve ACM style problems in many different languages. if you have 30 or so mins then check this http://codility.com/demo/run/ My weapon of choice is usually Java. So on of the problems I have is as follows (I will try to remember, should have taken a screenshot) Lets say you have array A[0]=1 A[1]=-1 ....A[n]=x Then what would be the smartest way to find out the number of times when A[i]+A[j] is even where i < j So if we have {1,2,3,4,5} we have 1+3 1+5 2+4 3+5 = 4 pairs which are even The code I wrote was some thing along the lines int sum=0; for(int i=0;i<A.length-1;i++){ for (int j=i+1;j<A.length;j++){ if( ((A[i]+A[j])%2) == 0 && i<j) { sum++; } } } There was one more restriction that if the number of pairs is greater than 1e9 then it should retrun -1, but lets forget it. Can you suggest a better solution for this. The number of elements won't exceed 1e9 in normal cases. I think I got 27 points deducted for the above code (ie it's not perfect). Codility gives out a detailed assessment of what went wrong, I don't have that right now.

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  • LINQ Query please help C#.Net.

    - by Paul Matthews
    I'm very new to LINQ and struggling to find the answers. I have a simple SQL query. Select ID, COUNT(ID) as Selections, OptionName, SUM(Units) as Units FROM tbl_Results GROUP BY ID, OptionName. The results I got were: '1' '4' 'Approved' '40' '2' '1' 'Rejected' '19' '3' '2' 'Not Decided' '12' Due to having to encrypt all my data in the database I'm unable to do sums. Therefore I have now brought back the data and decrypt it in the application layer. Results would be: '1' 'Approved' '10' '3' 'Not Deceided' '6' '2' 'Rejected' '19' '1' 'Approved' '15' '1' 'Approved' '5' '3' 'Not Deceided' '6' '1' 'Approved' '10' using a simple class I have called back the above results, and put them in a list class. public class results { public int ID {get;set;} public string OptionName {get;set;} public int Unit {get;set;} } I almost have the LINQ query to bring back the results like the SQL query at the top var q = from r in Results group p.Unit by p.ID int g select new {ID = g.Key, Selections = g.Count(), Units = g.Sum()}; How do I ensure my LINQ query also give me the Option Name? Also if I created a class called Statistics to hold my results how would I modify the LINQ query to give me list result set? public class results { public int ID {get;set;} public int NumberOfSelections { get; set; } public string OptionName {get;set;} public int UnitTotal {get;set;} }

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  • using a JOIN in an UPDATE in SQL

    - by SDLFunTimes
    Hi, I'm having trouble formulating a legal statement to double the statuses of the suppliers (s) who have shipped (sp) more than 500 units. I've been trying: update s set s.status = s.status * 2 from s join sp on (sp.sno = s.sno) group by sno having sum(qty) > 500; however I'm getting this error from Mysql: ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from s join sp on (sp.sno = s.sno) group by sno having sum(qty) > 500' at line 1 Does anyone have any ideas about what is wrong with this query? Here's my schema: create table s ( sno char(5) not null, sname char(20) not null, status smallint, city char(15), primary key (sno) ); create table p ( pno char(6) not null, pname char(20) not null, color char(6), weight smallint, city char(15), primary key (pno) ); create table sp ( sno char(5) not null, pno char(6) not null, qty integer not null, primary key (sno, pno) );

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  • Does query plan optimizer works well with joined/filtered table-valued functions?

    - by smoothdeveloper
    In SQLSERVER 2005, I'm using table-valued function as a convenient way to perform arbitrary aggregation on subset data from large table (passing date range or such parameters). I'm using theses inside larger queries as joined computations and I'm wondering if the query plan optimizer work well with them in every condition or if I'm better to unnest such computation in my larger queries. Does query plan optimizer unnest table-valued functions if it make sense? If it doesn't, what do you recommend to avoid code duplication that would occur by manually unnesting them? If it does, how do you identify that from the execution plan? code sample: create table dbo.customers ( [key] uniqueidentifier , constraint pk_dbo_customers primary key ([key]) ) go /* assume large amount of data */ create table dbo.point_of_sales ( [key] uniqueidentifier , customer_key uniqueidentifier , constraint pk_dbo_point_of_sales primary key ([key]) ) go create table dbo.product_ranges ( [key] uniqueidentifier , constraint pk_dbo_product_ranges primary key ([key]) ) go create table dbo.products ( [key] uniqueidentifier , product_range_key uniqueidentifier , release_date datetime , constraint pk_dbo_products primary key ([key]) , constraint fk_dbo_products_product_range_key foreign key (product_range_key) references dbo.product_ranges ([key]) ) go . /* assume large amount of data */ create table dbo.sales_history ( [key] uniqueidentifier , product_key uniqueidentifier , point_of_sale_key uniqueidentifier , accounting_date datetime , amount money , quantity int , constraint pk_dbo_sales_history primary key ([key]) , constraint fk_dbo_sales_history_product_key foreign key (product_key) references dbo.products ([key]) , constraint fk_dbo_sales_history_point_of_sale_key foreign key (point_of_sale_key) references dbo.point_of_sales ([key]) ) go create function dbo.f_sales_history_..snip.._date_range ( @accountingdatelowerbound datetime, @accountingdateupperbound datetime ) returns table as return ( select pos.customer_key , sh.product_key , sum(sh.amount) amount , sum(sh.quantity) quantity from dbo.point_of_sales pos inner join dbo.sales_history sh on sh.point_of_sale_key = pos.[key] where sh.accounting_date between @accountingdatelowerbound and @accountingdateupperbound group by pos.customer_key , sh.product_key ) go -- TODO: insert some data -- this is a table containing a selection of product ranges declare @selectedproductranges table([key] uniqueidentifier) -- this is a table containing a selection of customers declare @selectedcustomers table([key] uniqueidentifier) declare @low datetime , @up datetime -- TODO: set top query parameters . select saleshistory.customer_key , saleshistory.product_key , saleshistory.amount , saleshistory.quantity from dbo.products p inner join @selectedproductranges productrangeselection on p.product_range_key = productrangeselection.[key] inner join @selectedcustomers customerselection on 1 = 1 inner join dbo.f_sales_history_..snip.._date_range(@low, @up) saleshistory on saleshistory.product_key = p.[key] and saleshistory.customer_key = customerselection.[key] I hope the sample makes sense. Much thanks for your help!

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  • Mysql - Help me alter this search query to get desired results

    - by sandeepan-nath
    Following is a dump of the tables and data needed to answer understand the system:- The system consists of tutors and classes. The data in the table All_Tag_Relations stores tag relations for each tutor registered and each class created by a tutor. The tag relations are used for searching classes. CREATE TABLE IF NOT EXISTS `Tags` ( `id_tag` int(10) unsigned NOT NULL auto_increment, `tag` varchar(255) default NULL, PRIMARY KEY (`id_tag`), UNIQUE KEY `tag` (`tag`), KEY `id_tag` (`id_tag`), KEY `tag_2` (`tag`), KEY `tag_3` (`tag`), KEY `tag_4` (`tag`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; INSERT INTO `Tags` (`id_tag`, `tag`) VALUES (1, 'Sandeepan'), (2, 'Nath'), (3, 'first'), (4, 'class'), (5, 'new'), (6, 'Bob'), (7, 'Cratchit'); CREATE TABLE IF NOT EXISTS `All_Tag_Relations` ( `id_tag` int(10) unsigned NOT NULL default '0', `id_tutor` int(10) default NULL, `id_wc` int(10) unsigned default NULL, KEY `All_Tag_Relations_FKIndex1` (`id_tag`), KEY `id_wc` (`id_wc`), KEY `id_tag` (`id_tag`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; INSERT INTO `All_Tag_Relations` (`id_tag`, `id_tutor`, `id_wc`) VALUES (1, 1, NULL), (2, 1, NULL), (3, 1, 1), (4, 1, 1), (6, 2, NULL), (7, 2, NULL), (5, 2, 2), (4, 2, 2); Following is my query:- This query searches for "first class" (tag for first = 3 and for class = 4, in Tags table) and returns all those classes such that both the terms first and class are present in the class name. SELECT wtagrels.id_wc,SUM(DISTINCT( wtagrels.id_tag =3)) AS key_1_total_matches, SUM(DISTINCT( wtagrels.id_tag =4)) AS key_2_total_matches FROM all_tag_relations AS wtagrels WHERE ( wtagrels.id_tag =3 OR wtagrels.id_tag =4 ) GROUP BY wtagrels.id_wc HAVING key_1_total_matches = 1 AND key_2_total_matches = 1 LIMIT 0, 20 And it returns the class with id_wc = 1. But, I want the search to show all those classes such that all the search terms are present in the class name or its tutor name So that searching "Sandeepan class" (wtagrels.id_tag = 1,4) or "Sandeepan Nath" also returns the class with id_wc=1. And Searching. Searching "Bob First" should not return any classes. Please modify the above query or suggest a new query, if possible using MyIsam - fulltext search, but somehow help me get the result.

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  • Computing complex math equations in python

    - by dassouki
    Are there any libraries or techniques that simplify computing equations ? Take the following two examples: F = B * { [ a * b * sumOf (A / B ''' for all i ''' ) ] / [ sumOf(c * d * j) ] } where: F = cost from i to j B, a, b, c, d, j are all vectors in the format [ [zone_i, zone_j, cost_of_i_to_j], [..]] This should produce a vector F [ [1,2, F_1_2], ..., [i,j, F_i_j] ] T_ij = [ P_i * A_i * F_i_j] / [ SumOf [ Aj * F_i_j ] // j = 1 to j = n ] where: n is the number of zones T = vector [ [1, 2, A_1_2, P_1_2], ..., [i, j, A_i_j, P_i_j] ] F = vector [1, 2, F_1_2], ..., [i, j, F_i_j] so P_i would be the sum of all P_i_j for all j and Aj would be sum of all P_j for all i I'm not sure what I'm looking for, but perhaps a parser for these equations or methods to deal with multiple multiplications and products between vectors? To calculate some of the factors, for example A_j, this is what i use from collections import defaultdict A_j_dict = defaultdict(float) for A_item in TG: A_j_dict[A_item[1]] += A_item[3] Although this works fine, I really feel that it is a brute force / hacking method and unmaintainable in the case we want to add more variables or parameters. Are there any math equation parsers you'd recommend? Side Note: These equations are used to model travel. Currently I use excel to solve a lot of these equations; and I find that process to be daunting. I'd rather move to python where it pulls the data directly from our database (postgres) and outputs the results into the database. All that is figured out. I'm just struggling with evaluating the equations themselves. Thanks :)

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  • Issues with reversing bit shifts that roll over the maximum byte size?

    - by Terri
    I have a string of binary numbers that was originally a regular string and will return to a regular string after some bit manipulation. I'm trying to do a simple caesarian shift on the binary string, and it needs to be reversable. I've done this with this method.. public static String cShift(String ptxt, int addFactor) { String ascii = ""; for (int i = 0; i < ptxt.length(); i+=8) { int character = Integer.parseInt(ptxt.substring(i, i+8), 2); byte sum = (byte) (character + addFactor); ascii += (char)sum; } String returnToBinary = convertToBinary(ascii); return returnToBinary; } This works fine in some cases. However, I think when it rolls over being representable by one byte it's irreversable. On the test string "test!22*F ", with an addFactor of 12, the string becomes irreversible. Why is that and how can I stop it?

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  • Query Access and VB.NET

    - by yae
    Hi all: I have 2 tables: "products" and "pieces" PRODUCTS idProd product price PIECES id idProdMain idProdChild quant idProdMain and idProdChild are vinculated with the table: "products". Other considerations is that 1 product can have some pieces and 1 product can be a piece. Price product equal a sum of quantity * price of all their pieces. EXAMPLE: TABLE PRODUCTS (idProd - product - price) 1 - Computer - 300€ 2 - Hard Disk - 100€ 3 - Memory - 50€ 4 - Main Board - 100€ 5 - Software - 50€ 6 - CDroms 100 un. - 30€ TABLE PIECES (id - idProdMain - idProdChild - Quant.) 1 - 1 - 2 - 1 2 - 1 - 3 - 2 3 - 1 - 4 - 1 WHAT I NEED? I need update the price of the main product when the price of the product child (piece) is changed. Following the previous example, if I change the price of this product "memory" (is a piece too) to 60€, then product "Computer" will must change his price to 320€ How I can do it using queries? Already I have tried this to obatin the price of the main product, but not runs. This query not returns any value SELECT Sum(products.price*pieces.quant) AS Expr1 FROM products LEFT JOIN pieces ON (products.idProd = pieces.idProdChild) AND (products.idProd = pieces.idProdChild) AND (products.idProd = pieces.idProdMain) WHERE (((pieces.idProdMain)=5));

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  • Can't get recursive function to work in Java

    - by Ahmed Salah
    I read docs about java recorsion and I thought I have understood it, but when I try to use it in the following example, it does not work as expected. I a class account, which has amount and can have forther subAccount. I would have implemented one method getSum, which has to return the summ of the amount of the account and amount of all of its subaccount. In the following code, the call of the method getSumm() should return 550, but it behaves strange. can somebody help please? public class Balance{ ArrayList<Balance> subAccounts = new ArrayList<Balance>(); String accountID = null; Double amount = null; double result=0; public double getSum(ArrayList<Balance> subAccounts){ if(subAccounts !=null && subAccounts.size()>0){ for (int i = 0; i < subAccounts.size(); i++) { result = result + getSum(subAccounts.get(i).subAccounts); } } else { return amount; } return result; } public static void main(String[] args) { Balance bs1 = new Balance(); Balance bs2 = new Balance(); Balance bs3 = new Balance(); bs1.amount=100.0; bs2.amount=150.0; bs3.amount=300.0; ArrayList<Balance> subAccounts1 = new ArrayList<Balance>(); bs2.subAccounts=null; bs3.subAccounts=null; subAccounts1.add(bs2); subAccounts1.add(bs3); bs1.subAccounts=subAccounts1; double sum= bs1.getSum(subAccounts1); System.out.println(sum); } }

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  • Help Me With This Access Query

    - by yae
    I have 2 tables: "products" and "pieces" PRODUCTS idProd product price PIECES id idProdMain idProdChild quant idProdMain and idProdChild are related with the table: "products". Other considerations is that 1 product can have some pieces and 1 product can be a piece. Price product equal a sum of quantity * price of all their pieces. "Products" table contains all products (p EXAMPLE: TABLE PRODUCTS (idProd - product - price) 1 - Computer - 300€ 2 - Hard Disk - 100€ 3 - Memory - 50€ 4 - Main Board - 100€ 5 - Software - 50€ 6 - CDroms 100 un. - 30€ TABLE PIECES (id - idProdMain - idProdChild - Quant.) 1 - 1 - 2 - 1 2 - 1 - 3 - 2 3 - 1 - 4 - 1 WHAT I NEED? I need update the price of the main product when the price of the product child (piece) is changed. Following the previous example, if I change the price of this product "memory" (is a piece too) to 60€, then product "Computer" will must change his price to 320€ How I can do it using queries? Already I have tried this to obatin the price of the main product, but not runs. This query not returns any value: SELECT Sum(products.price*pieces.quant) AS Expr1 FROM products LEFT JOIN pieces ON (products.idProd = pieces.idProdChild) AND (products.idProd = pieces.idProdChild) AND (products.idProd = pieces.idProdMain) WHERE (((pieces.idProdMain)=5)); MORE INFO The table "products" contains all the products to sell that it is in the shop. The table "pieces" is to take a control of the compound products. To know those who are the products children. For example of compound product: computers. This product is composed by other products (motherboard, hard disk, memory, cpu, etc.)

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  • MySQL Stored Procedures not working with SELECT (basic question)

    - by TMG
    Hello, I am using a platform (perfectforms) that requires me to use stored procedures for most of my queries, and having never used stored procedures, I can't figure out what I'm doing wrong. The following statement executes without error: DELIMITER // DROP PROCEDURE IF EXISTS test_db.test_proc// CREATE PROCEDURE test_db.test_proc() SELECT 'foo'; // DELIMITER ; But when I try to call it using: CALL test_proc(); I get the following error: #1312 - PROCEDURE test_db.test_proc can't return a result set in the given context I am executing these statements from within phpmyadmin 3.2.4, PHP Version 5.2.12 and the mysql server version is 5.0.89-community. When I write a stored procedure that returns a parameter, and then select it, things work fine (e.g.): DELIMITER // DROP PROCEDURE IF EXISTS test_db.get_sum// CREATE PROCEDURE test_db.get_sum(out total int) BEGIN SELECT SUM(field1) INTO total FROM test_db.test_table; END // DELIMITER ; works fine, and when I call it: CALL get_sum(@t); SELECT @t; I get the sum no problem. Ultimately, what I need to do is have a fancy SELECT statement wrapped up in a stored procedure, so I can call it, and return multiple rows of multiple fields. For now I'm just trying to get any select working. Any help is greatly appreciated.

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  • Confused about definition of a 'median' when constructing a kd-Tree

    - by user352636
    Hi there. Im trying to build a kd-tree for searching through a set of points, but am getting confused about the use of 'median' in the wikipedia article. For ease of use, the wikipedia article states the pseudo-code of kd-tree construction as: function kdtree (list of points pointList, int depth) { if pointList is empty return nil; else { // Select axis based on depth so that axis cycles through all valid values var int axis := depth mod k; // Sort point list and choose median as pivot element select median by axis from pointList; // Create node and construct subtrees var tree_node node; node.location := median; node.leftChild := kdtree(points in pointList before median, depth+1); node.rightChild := kdtree(points in pointList after median, depth+1); return node; } } I'm getting confused about the "select median..." line, simply because I'm not quite sure what is the 'right' way to apply a median here. As far as I know, the median of an odd-sized (sorted) list of numbers is the middle element (aka, for a list of 5 things, element number 3, or index 2 in a standard zero-based array), and the median of an even-sized array is the sum of the two 'middle' elements divided by two (aka, for a list of 6 things, the median is the sum of elements 3 and 4 - or 2 and 3, if zero-indexed - divided by 2.). However, surely that definition does not work here as we are working with a distinct set of points? How then does one choose the correct median for an even-sized list of numbers, especially for a length 2 list? I appreciate any and all help, thanks! -Stephen

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