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  • C++ Urban Myths

    - by Neil Butterworth
    I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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  • O'Reilly book clarification on 2d linear system

    - by Eric
    The Oreilly book "Learning openCV" states at page 356 : Quote Before we get totally lost, let’s consider a particular realistic situation of taking measurements on a car driving in a parking lot. We might imagine that the state of the car could be summarized by two position variables, x and y, and two velocities, vx and vy. These four variables would be the elements of the state vector xk. Th is suggests that the correct form for F is: x = [ x; y; vx; vy; ]k F = [ 1, 0, dt, 0; 0, 1, 0, dt; 0, 0, 1, 0; 0, 0, 0, 1; ] It seems natural to put 'dt' just there in the F matrix but I just don't get why. What if I have a n states system, how would I spray some "dt" in the F matrix?

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  • VPS goes slow at more than 20 users online at the same time

    - by hachiari
    I have 512 MB VPS (brustable to 1GB) Somehow, the site goes slow when there are about 10 users, and becomes impossible to load at 20 users online at the same time. I wonder what could be the problem for this. The bandwidth connection of the VPS is 1Gbps. Here is some settings in my VPS: KeepAlive Off <IfModule prefork.c> StartServers 7 MinSpareServers 7 MaxSpareServers 10 ServerLimit 64 MaxClients 64 MaxRequestsPerChild 0 </IfModule> my.cnf settings - calculated Max Memory 300MB Output from UNIXBENCH INDEX VALUES TEST BASELINE RESULT INDEX Dhrystone 2 using register variables 376783.7 13429727.4 356.4 Double-Precision Whetstone 83.1 1137.5 136.9 Execl Throughput 188.3 1637.4 87.0 File Copy 1024 bufsize 2000 maxblocks 2672.0 148868.0 557.1 File Copy 256 bufsize 500 maxblocks 1077.0 79430.0 737.5 File Read 4096 bufsize 8000 maxblocks 15382.0 1410009.0 916.7 Pipe Throughput 111814.6 4419722.0 395.3 Pipe-based Context Switching 15448.6 561505.1 363.5 Process Creation 569.3 10272.7 180.4 Shell Scripts (8 concurrent) 44.8 514.3 114.8 System Call Overhead 114433.5 3537373.8 309.1 ========= FINAL SCORE 295.0 I am afraid that the VPS company limit the number of connection to the VPS... is it possible? The server is in Japan, but the site has global traffic (some of the traffic are from countries with low speed connection). Could this be the problem? This is a serious problem :( my site just cant grow if this keeps on happening... please tell me if you have any idea. Thank You, Bryant

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  • How to interpolate rotations?

    - by uhuu
    I have two vectors describing rotations; a start rotation A and a target rotation B. How would I best go about interpolating A by a factor F to approach B? Using a simple lerp on the vectors fails to work when more than one dimension needs to be interpolated (i.e. produces undesirable rotations). Maybe building quaternions from the rotation vectors and using slerp is the way to go. But how, then, could I extract a vector describing the new rotation from the resulting quaternion? Thanks in advance.

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  • Multiset of shared_ptrs as a dynamic priority queue: Concept and practice

    - by Sarah
    I was using a vector-based priority queue typedef std::priority_queue< Event, vector< Event >, std::greater< Event > > EventPQ; to manage my Event objects. Now my simulation has to be able to find and delete certain Event objects not at the top of the queue. I'd like to know if my planned work-around can do what I need it to, and if I have the syntax right. I'd also like to know if dramatically better solutions exist. My plan is to make EventPQ a multiset of smart pointers to Event objects: typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; I'm borrowing functions of the Event class from a related post on a multimap priority queue. // Event.h #include <cstdlib> using namespace std; #include <set> #include <boost/shared_ptr.hpp> class Event; typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; class Event { public: Event( double t, int eid, int hid ); ~Event(); void add( EventPQ& q ); void remove(); bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } bool operator > ( const Event & rhs ) const { return ( time > rhs.time ); } double time; int eventID; int hostID; EventPQ* mq; EventPQ::iterator mIt; }; // Event.cpp Event::Event( double t, int eid, int hid ) { time = t; eventID = eid; hostID = hid; } Event::~Event() {} void Event::add( EventPQ& q ) { mq = &q; mIt = q.insert( boost::shared_ptr<Event>(this) ); } void Event::remove() { mq.erase( mIt ); mq = 0; mIt = EventPQ::iterator(); } I was hoping that by making EventPQ a container of pointers, I could avoid wasting time copying Events into the container and avoid accidentally editing the wrong copy. Would it be dramatically easier to store the Events themselves in EventPQ instead? Does it make more sense to remove the time keys from Event objects and use them instead as keys in a multimap? Assuming the current implementation seems okay, my questions are: Do I need to specify how to sort on the pointers, rather than the objects, or does the multiset automatically know to sort on the objects pointed to? If I have a shared_ptr ptr1 to an Event that also has a pointer in the EventPQ container, how do I find and delete the corresponding pointer in EventPQ? Is it enough to .find( ptr1 ), or do I instead have to find by the key (time)? Is the Event::remove() sufficient for removing the pointer in the EventPQ container? There's a small chance multiple events could be created with the same time (obviously implied in the use of multiset). If the find() works on event times, to avoid accidentally deleting the wrong event, I was planning to throw in a further check on eventID and hostID. Does this seem reasonable? (Dumb syntax question) In Event.h, is the declaration of dummy class Event;, then the EventPQ typedef, and then the real class Event declaration appropriate? I'm obviously an inexperienced programmer with very spotty background--this isn't for homework. Would love suggestions and explanations. Please let me know if any part of this is confusing. Thanks.

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  • How to make negate_unary work with any type?

    - by Chan
    Hi, Following this question: How to negate a predicate function using operator ! in C++? I want to create an operator ! can work with any functor that inherited from unary_function. I tried: template<typename T> inline std::unary_negate<T> operator !( const T& pred ) { return std::not1( pred ); } The compiler complained: Error 5 error C2955: 'std::unary_function' : use of class template requires template argument list c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 223 1 Graphic Error 7 error C2451: conditional expression of type 'std::unary_negate<_Fn1>' is illegal c:\program files\microsoft visual studio 10.0\vc\include\ostream 529 1 Graphic Error 3 error C2146: syntax error : missing ',' before identifier 'argument_type' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 4 error C2065: 'argument_type' : undeclared identifier c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 2 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 6 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 230 1 Graphic Any idea? Update Follow "templatetypedef" solution, I got new error: Error 3 error C2831: 'operator !' cannot have default parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 2 error C2808: unary 'operator !' has too many formal parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 4 error C2675: unary '!' : 'is_prime' does not define this operator or a conversion to a type acceptable to the predefined operator c:\visual studio 2010 projects\graphic\graphic\main.cpp 52 1 Graphic Update 1 Complete code: #include <iostream> #include <functional> #include <utility> #include <cmath> #include <algorithm> #include <iterator> #include <string> #include <boost/assign.hpp> #include <boost/assign/std/vector.hpp> #include <boost/assign/std/map.hpp> #include <boost/assign/std/set.hpp> #include <boost/assign/std/list.hpp> #include <boost/assign/std/stack.hpp> #include <boost/assign/std/deque.hpp> struct is_prime : std::unary_function<int, bool> { bool operator()( int n ) const { if( n < 2 ) return 0; if( n == 2 || n == 3 ) return 1; if( n % 2 == 0 || n % 3 == 0 ) return 0; int upper_bound = std::sqrt( static_cast<double>( n ) ); for( int pf = 5, step = 2; pf <= upper_bound; ) { if( n % pf == 0 ) return 0; pf += step; step = 6 - step; } return 1; } }; /* template<typename T> inline std::unary_negate<T> operator !( const T& pred, typename T::argument_type* dummy = 0 ) { return std::not1<T>( pred ); } */ inline std::unary_negate<is_prime> operator !( const is_prime& pred ) { return std::not1( pred ); } template<typename T> inline void print_con( const T& con, const std::string& ms = "", const std::string& sep = ", " ) { std::cout << ms << '\n'; std::copy( con.begin(), con.end(), std::ostream_iterator<typename T::value_type>( std::cout, sep.c_str() ) ); std::cout << "\n\n"; } int main() { using namespace boost::assign; std::vector<int> nums; nums += 1, 3, 5, 7, 9; nums.erase( remove_if( nums.begin(), nums.end(), !is_prime() ), nums.end() ); print_con( nums, "After remove all primes" ); } Thanks, Chan Nguyen

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  • Mono Ignores Graphics.InterpolationMode?

    - by Timothy Baldridge
    I have a program that draws some vector graphics using System.Drawing and the Graphics class. The anti-aliasing works, kindof okay, but for my need I neede oversampling, so I create the starting image to be n times larger and then scale back the final image by n. On Window and .NET the resulting image looks great! However, on Mono 2.4.2.3 (Ubuntu 9.10 stock install), the intropolation is horrible. Here's how I'm scaling my images: Bitmap bmp = new Bitmap(Bmp.Width / OverSampling, Bmp.Height / OverSampling); Graphics g = Graphics.FromImage(bmp); g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.DrawImage(Bmp, 0, 0, bmp.Width, bmp.Height); g.Dispose(); From what I can tell there is no interpolation happening at all. Any ideas?

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  • Why is my server performance degrading to the point of stopping, periodically?

    - by Pascal Aschwanden
    So, once in a while, I see in firebug that a request takes over 15 or even 60 seconds to respond and sometimes never. Here is what I've ruled out: It's not the CPU, cuz every time I check the Server load its less then 6 for all 3 numbers It's not the memory, because thats fairly low too, less the 50% It's not the I/O anymore, because I've seen the graphs that Joyent sent back to me when I requested them, and they show less then 3MB of I/O (mostly all read). It's not the SQL performance - I've profiled every last SQL command that runs, and they're all (99.9% of them anyway) running in less then 30ms, most run in less then 5ms. Oh and I've been profiling all the script execution times, and even the when the problem occurs, the script always manages to finish in 50ms or less (that's 1 / 20th of a second ). Now, I do run alot of ajax calls. 1 every 2 seconds per user and I have 300 DAU+. But, even if all 300 are playing simultaneously, thats still only 150 calls per second max. The only other thing I can think of is that one of my neighbors is funky. The problem is highly intermittent. 99% of the time it works perfectly and there's excellent performance. but 99%+ is not good enough. Eventually the performance gets so bad I have to restart the server, at which point everything is fine again. I've done this about 4 times now. Any ideas? Note: this is on joyent, vps, intro package 256mb of ram with bursting. here are the mysql dump info: Traffic ø per hour Received 18 MiB 29 MiB Sent 134 MiB 221 MiB Total 151 MiB 251 MiB Connections ø per hour % max. concurrent connections 5 --- --- Failed attempts 0 0.00 0.00% Aborted 0 0.00 0.00% Total 9,418 15.59 k 100.00%

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  • Container for database-like searches

    - by Milan Babuškov
    I'm looking for some STL, boost, or similar container to use the same way indexes are used in databases to search for record using a query like this: select * from table1 where field1 starting with 'X'; or select * from table1 where field1 like 'X%'; I thought about using std::map, but I cannot because I need to search for fields that "start with" some text, and not those that are "equal to". I could create a sorted vector or list and use binary search (breaking the set in 2 in each step by reading the element in the middle and seeing if it's more or less than 'X'), but I wonder if there is some ready-made container I could use without reinventing the wheel?

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  • 150 TB and growing, but how to grow?

    - by seandavi
    My group currently has two largish storage servers, both NAS running debian linux. The first is an all-in-one 24-disk (SATA) server that is several years old. We have two hardware RAIDS set up on it with LVM over those. The second server is 64 disks divided over 4 enclosures, each a hardware RAID 6, connected via external SAS. We use XFS with LVM over that to create 100TB useable storage. All of this works pretty well, but we are outgrowing these systems. Having build two such servers and still growing, we want to build something that allows us more flexibility in terms of future growth, backup options, that behaves better under disk failure (checking the larger filesystem can take a day or more), and can stand up in a heavily concurrent environment (think small computer cluster). We do not have system administration support, so we administer all of this ourselves (we are a genomics lab). So, what we seek is a relatively low-cost, acceptable performance storage solution that will allow future growth and flexible configuration (think ZFS with different pools having different operating characteristics). We are probably outside the realm of a single NAS. We have been thinking about a combination of ZFS (on openindiana, for example) or btrfs per server with glusterfs running on top of that if we do it ourselves. What we are weighing that against is simply biting the bullet and investing in Isilon or 3Par storage solutions. Any suggestions or experiences are appreciated.

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  • java.lang.NullPointerException exception in my controller file (using Spring Hibernate Maven)

    - by mrjayviper
    The problem doesn't seemed to have anything to do with Hibernate. As I've commented the Hibernate stuff but I'm still getting it. If I comment out this line message = staffDAO.searchForStaff(search); in my controller file, it goes through ok. But I don't see anything wrong with searchForStaff function. It's a very simple function that just returns the string "test" and run system.out.println("test"). Can you please help? thanks But this is the error that I'm getting: SEVERE: Servlet.service() for servlet [spring] in context with path [/directorymaven] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause java.lang.NullPointerException at org.flinders.staffdirectory.controllers.SearchController.showSearchResults(SearchController.java:25) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:100) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:604) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:565) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778) at javax.servlet.http.HttpServlet.service(HttpServlet.java:621) at javax.servlet.http.HttpServlet.service(HttpServlet.java:728) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) My spring-servlet xml <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"> <context:component-scan base-package="org.flinders.staffdirectory.controllers" /> <mvc:annotation-driven /> <mvc:resources mapping="/resources/**" location="/resources/" /> <tx:annotation-driven /> <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer" p:location="/WEB-INF/spring.properties" /> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${jdbc.driverClassName}" p:url="${jdbc.databaseurl}" p:username="${jdbc.username}" p:password="${jdbc.password}" /> <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean" p:dataSource-ref="dataSource" p:configLocation="${hibernate.config}" p:packagesToScan="org.flinders.staffdirectory"/> <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager" p:sessionFactory-ref="sessionFactory" /> <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver" p:viewClass="org.springframework.web.servlet.view.tiles2.TilesView" /> <bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer" p:definitions="/WEB-INF/tiles.xml" /> <bean id="staffDAO" class="org.flinders.staffdirectory.dao.StaffDAO" p:sessionFactory-ref="sessionFactory" /> <!-- <bean id="staffService" class="org.flinders.staffdirectory.services.StaffServiceImpl" p:staffDAO-ref="staffDAO" />--> </beans> This is my controller file package org.flinders.staffdirectory.controllers; import java.util.List; //import org.flinders.staffdirectory.models.database.SearchResult; import org.flinders.staffdirectory.models.misc.Search; import org.flinders.staffdirectory.dao.StaffDAO; //import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.ModelAttribute; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.servlet.ModelAndView; @Controller public class SearchController { //@Autowired private StaffDAO staffDAO; private String message; @RequestMapping("/SearchStaff") public ModelAndView showSearchResults(@ModelAttribute Search search) { //List<SearchResult> searchResults = message = staffDAO.searchForStaff(search); //System.out.println(search.getSurname()); return new ModelAndView("search/SearchForm", "Search", new Search()); //return new ModelAndView("search/SearchResults", "searchResults", searchResults); } @RequestMapping("/SearchForm") public ModelAndView showSearchForm() { return new ModelAndView("search/SearchForm", "search", new Search()); } } my dao class package org.flinders.staffdirectory.dao; import java.util.List; import org.hibernate.SessionFactory; //import org.springframework.beans.factory.annotation.Autowired; import org.flinders.staffdirectory.models.database.SearchResult; import org.flinders.staffdirectory.models.misc.Search; public class StaffDAO { //@Autowired private SessionFactory sessionFactory; public void setSessionFactory(SessionFactory sessionFactory) { this.sessionFactory = sessionFactory; } public String searchForStaff(Search search) { /*String SQL = "select distinct telsumm_id as id, telsumm_parent_id as parentId, telsumm_name_title as title, (case when substr(telsumm_surname, length(telsumm_surname) - 1, 1) = ',' then substr(telsumm_surname, 1, length(telsumm_surname) - 1) else telsumm_surname end) as surname, telsumm_preferred_name as firstname, nvl(telsumm_tele_number, '-') as telephoneNumber, nvl(telsumm_role, '-') as role, telsumm_display_department as department, lower(telsumm_entity_type) as entityType from teldirt.teld_summary where (telsumm_search_surname is not null) and not (nvl(telsumm_tele_directory,'xxx') IN ('N','S','D')) and not (telsumm_tele_number IS NULL AND telsumm_alias IS NULL) and (telsumm_alias_list = 'Y' OR (telsumm_tele_directory IN ('A','B'))) and ((nvl(telsumm_system_id_end,sysdate+1) > SYSDATE and telsumm_entity_type = 'P') or (telsumm_entity_type = 'N')) and (telsumm_search_department NOT like 'SPONSOR%')"; if (search.getSurname().length() > 0) { SQL += " and (telsumm_search_surname like '" + search.getSurname().toUpperCase() + "%')"; } if (search.getSurnameLike().length() > 0) { SQL += " and (telsumm_search_soundex like soundex(('%" + search.getSurnameLike().toUpperCase() + "%'))"; } if (search.getFirstname().length() > 0) { SQL += " and (telsumm_search_preferred_name like '" + search.getFirstname().toUpperCase() + "%' or telsumm_search_first_name like '" + search.getFirstname() + "%')"; } if (search.getTelephoneNumber().length() > 0) { SQL += " and (telsumm_tele_number like '" + search.getTelephoneNumber() + "%')"; } if (search.getDepartment().length() > 0) { SQL += " and (telsumm_search_department like '" + search.getDepartment().toUpperCase() + "%')"; } if (search.getRole().length() > 0) { SQL += " and (telsumm_search_role like '" + search.getRole().toUpperCase() + "%')"; } SQL += " order by surname, firstname"; List<Object[]> list = (List<Object[]>) sessionFactory.getCurrentSession().createQuery(SQL).list(); for(int j=0;j<list.size();j++){ Object [] obj= (Object[])list.get(j); for(int i=0;i<obj.length;i++) System.out.println(obj[i]); }*/ System.out.println("test"); return "test"; } }

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  • MATLAB: draw centroids

    - by Myx
    Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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  • C++ boost ublas + units dimension constraints

    - by aaa
    hello. I am seeking advice on design/general idea on how to force matrix dimension constraints on ublas matrix/vector possibly using boost units. For example, let matrix A have dimensions of time x force (for example) // does not have dimensions, time x force and force x time are not distinguished. matrix<double> A; //something like? dimension<time, force, matrix<double> > A; dimension<force, time, matrix<double> > B = trans(A); have you done something like this or do you have some good idea about how to organize such constraints? Thank you

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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  • Read multiple strings from a file C++

    - by user69514
    Hi I need to read different values stored in a file one by one. So I was thinking I can use ifstream to open the file, but since the file is set up in such a way that a line might contain three numbers, and the other line one number or two numbers I'm not sure how to read each number one by one. I was thinking of using stringstream but I'm not sure if that would work. The file is a format like this. 52500.00 64029.50 56000.00 65500.00 53780.00 77300.00 44000.50 80100.20 90000.00 41000.00 60500.50 72000.00 I need to read each number and store it in a vector. What is the best way to accomplish this? Reading one number at a time even though each line contains a different amount of numbers?

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  • Distance between hyperplanes

    - by michael dillard
    I'm trying to teach myself some machine learning, and have been using the MNIST database (http://yann.lecun.com/exdb/mnist/) do so. The author of that site wrote a paper in '98 on all different kinds of handwriting recognition techniques, available at http://yann.lecun.com/exdb/publis/pdf/lecun-98.pdf. The 10th method mentioned is a "Tangent Distance Classifier". The idea being that if you place each image in a (NxM)-dimensional vector space, you can compute the distance between two images as the distance between the hyperplanes formed by each where the hyperplane is given by taking the point, and rotating the image, rescaling the image, translating the image, etc. I can't figure out enough to fill in the missing details. I understand that most of these are indeed linear operators, so how does one use that fact to then create the hyperplane? And once we have a hyperplane, how do we take its distance with other hyperplanes?

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  • Matlab Question - Principal Component Analysis

    - by Jack
    I have a set of 100 observations where each observation has 45 characteristics. And each one of those observations have a label attached which I want to predict based on those 45 characteristics. So it's an input matrix with the dimension 45 x 100 and a target matrix with the dimension 1 x 100. The thing is that I want to know how many of those 45 characteristics are relevant in my set of data, basically the principal component analysis, and I understand that I can do this with Matlab function processpca. Could you please tell me how can I do this? Suppose that the input matrix is x with 45 rows and 100 columns and y is a vector with 100 elements.

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  • OpenLayers: Get resolution of map in a given projection (4326)

    - by David Pfeffer
    I'm using OpenLayers to display OpenStreetMap maps. (Though, I'd assume this should be general enough to work for any map product...) I'm displaying some very sophisticated vector overlays, and the amount and resolution of the features I'm returning from the server via GeoJSON to overlay has proven too much for many computers. What I'd like to do now instead is to only send data befitting the resolution of the current zoom. This should be relatively easy to do using the getResolution and calculateBounds methods on the Map object. calculateBounds returns a Bounds object that then can be transformed between the map projection and display projection. How do I transform the resolution into my desired projection (4326 in this case)?

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  • How might I assume a "default value" when parsing using boost::spirit?

    - by tJener
    Let's say I have a grammar defined to something like: a b c d where c, and d are optional and default to 14 if not given. Can I get it to automatically return the 14 if the value isn't given? The closest I've come is like the following: qi::rule<Iterator, std::vector<int>(), ascii::space_type> some_rule; some_rule %= >> int_ >> int_ >> -int_ >> -int_; // ... some_other_rule = some_rule[&some_callback_for_int_vectors]; which will then get 0 for the optional values that didn't show up (I believe). I then change consecutive 0s at the end into 14. Not only is this horribly wrong, but its also just not elegant. Is there a better way to do this?

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  • Reducing template bloat with inheritance

    - by benoitj
    Does anyone have experience reducing template code bloat using inheritance? i hesitate rewriting our containers this way: class vectorBase { public: int size(); void clear(); int m_size; void *m_rawData; //.... }; template< typename T > class vector : public vectorBase { void push_back( const T& ); //... }; I should keep maximum performance while reducing compile time I'm also wondering why stl implementations do not uses this approach Thanks for your feedbacks

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  • the problem only happens when i try create a release...

    - by ace
    I'm sorry if im not presenting this right, but i trully cannot understand what the problem is. i have a project to hand in, a code of 600 lines defined within a main, .cpp, and header file. if i compile the project with just a debugger and no release, it's fine. when i create it with the release, the following error occurs, for every function!!! 1st error: |36|multiple definition of `countLines(int&, std::vector const&)'| 2nd error: |36|first defined here| if someone will allow me and i can send them the entire code, that would be awesome - i have to have this done within 3 hours.

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  • C++ refactor common code with one different statement

    - by user231536
    I have two methods f(vector<int>& x, ....) and g(DBConn& x, ....) where the (....) parameters are all identical. The code inside the two methods are completely identical except for one statement where we do different actions based on the type of x: in f(): we do x.push_back(i) in g(): we do x.DeleteRow(i) What is the simplest way to extract the common code into one method and yet have the two different statements? I am thinking of having a templated functor that overloads operator () (int a) but that seems overkill.

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  • Interpreter in C++: Function table storage problem

    - by sub
    In my interpreter I have built-in functions available in the language like print exit input, etc. These functions can obviously be accessed from inside the language. The interpreter then looks for the corresponding function with the right name in a vector and calls it via a pointer stored with its name. So I gather all these functions in files like io.cpp, string.cpp, arithmetic.cpp. But I have to add every function to the function list in the interpreter in order for it to be found. So in these function files I have things like: void print( arg ) { cout << arg.ToString; } I'd add this print function to the interpreter function list with: interpreter.AddFunc( "print", print ); But where should I call the interpreter.AddFunc? I can't just put it there below the print function as it has to be in a function according to the C++ syntax. Where and how should all the functions be added to the list?

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  • Fast, Vectorizable method of taking floating point number modulus of special primes?

    - by caffiend
    Is there a fast method for taking the modulus of a floating point number? With integers, there are tricks for Mersenne primes, so that its possible to calculate y = x MOD 2^31 without needing division. Can any similar tricks be applied for floating point numbers? Preferably, in a way that can be converted into vector/SIMD operations, or moved into GPGPU code. The primes I'm interested in would be 2^7 and 2^31, although if there are more efficient ones for floating point numbers, those would be welcome.

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  • ingenious idea needed: how to declare different sizes for different fonts? @font-face?

    - by Haroldo
    I've never seen this done, but i get a feeling that there's gotta be a clever way of doing it. css font-size-adjust looks like it was never meant to be, but when i look around I'm seeing some really ingenious css techniques going on. Take this on nettuts yesterday for using @font-face for vector icons. my challenge: if(user has calibri ) { font-family: calibri; font-size: 12px; } if(user hasn't calibri ) { font-family: arial; font-size: 10px; }

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