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[odeint] optional data
by Erik Schultheis 22 Jul '14

22 Jul '14

Dear all, i am simulating particle trajectories, and depending on the data i want to generate i may or may not have to track additional data [boost.ublas c_matrix] along those trajectories. Right now i enable/disable that via a template parameter (so, using std::tuple(vec, vec) or tuple(vec, vec, c_matrix) and fusion_algebra), which has a few drawbacks. The algorithm is already templated to support varying dimensions via a template parameter, so the additional data practically doubles the number of template instantiations for system and all possible observers. This actually got so bad that gcc (mingw gcc 4.8) refuses to compile with debugging enabled. Therefore, i would like to make the switch between tracking the matrix and ignoring it a runtime choice instead of a template parameter. However, the cost of tracking that matrix is quite high (that is why it is optional), but simply disableing the d matrix / dt calculation in the system does not speed up the calculation much (86 s -> 58 s vs 27 s without matrix). A lot of time is spent in adding and multiplying numbers that are not used anywhere, or actually even copying them (e.g std::swap(c_matrix, c_matrix) shows up quite high in gprof (even though i am not sure how reliable the -pg option is in conjunction with -O3)). So what i am asking here is for suggestions how to best let odeint treat the c_matrix as uninitialized memory and never perform any operations on that depending on a runtime parameter. Options i thought of were: * deriving a class from c_matrix and providing my own versions of operator overloads that check a flag: as far as i know, boost.ublas matrices use some template magic to let operators only return expression templates to optimize evaluation if operations are chained, and i would not be sure about how to actually retain that behaviour in case the matrix is tracked. * creating my own algebra class: from what i could tell from a few quick glances into the algebra files, this would probably be conceptually easier than the other option, but would require a lot of repetetive coding. Does anyone have suggestion for a more efficient implementation strategy? Greetings Erik

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[type traits] redefine a type trait
by Michael Powell 21 Jul '14

21 Jul '14

Hello, Question: is there a way to delete or remove a type trait once it has been defined? And/or redefine it? Consider, I've got a default type trait, something like this. template<typename T> struct throws_exceptions { static const bool value = true; }; struct my_object { //does some work with or without exception }; template<> struct throws_exceptions<my_object> { static const bool value = false; } However, in my unit test code, I want to override the default behavior for test purposes. template<> struct throws_exceptions<my_object> { static const bool value = true; } Or just leave the type trait out. Actually, I'm not sure I just considered an answer to my own question. Possibly I need to separate the traits from the underlying things being modified, and leave it as an option whether to include the defaults, or define user-provided traits. Best regards, Michael Powell

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[msm] enque vs defer
by Raj Sambasivan 21 Jul '14

21 Jul '14

Hi boost-users/Christophe, Does enqueue and defer use the same underlying queue, and when i defer can i validate my unit testcase to check on the queue size using get_message_queue_size(). I did a quick test on defer and checking the queue size and it didnt work may be there is something wrong in my test program but wanted to check if anyone tried this out. thank you -raj

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linking err using log
by David Frank 20 Jul '14

20 Jul '14

Has anyone seen this:? boost/log/attributes/attribute_value_impl.hpp:47: undefined reference to `boost::log::v2s_mt_posix::attribute::impl::operator delete(void*, unsigned long)' In function `boost::log::v2s_mt_posix::attributes::attribute_value_impl<boost::posix_time::ptime>::~attribute_value_impl()': Thanks, Dave

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Push-Relabel undirected graph
by Charles Maske 20 Jul '14

20 Jul '14

Hi there, I'm working in a cut-tree implementation of gomoryhu algorithm and I have to compute max-flow on the input graph. I read about efficiency of the push-relabel algorithm and I want to do some tests but I can't get this because all reverse edges have to capacity equals 0. Someone knows one way to workaround this restriction? Other max-flow algorithms in BGL (edmonds-karp and boykov-kolmogorov) don't have this restriction, what do them more fast than push-relabel implementation. Thanks

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Generate random graphs
by Mandy Nour 20 Jul '14

20 Jul '14

Hello all, I need to generate random undirected simple graphs using The Erdos-Rényi methods and to extract its adjacency matrix into an std::vector. -- View this message in context: http://boost.2283326.n4.nabble.com/Generate-random-graphs-tp4665336.html Sent from the Boost - Users mailing list archive at Nabble.com.

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[variant] forward declarations
by Michael Powell 18 Jul '14

18 Jul '14

Hello, I've got some structs in a AST of sorts which the main player in the mix is a node. In at least one of the use cases, one of the variant types must be forward declared at the time the node can be declared. Possibly one or two other similar use cases. Error 2 error C2139: 'xml::xelement' : an undefined class is not allowed as an argument to compiler intrinsic type trait '__is_nothrow_constructible' i:\installs\development\boost.org\1.55.0\boost_1_55_0\stage\include\boost\type_traits\has_nothrow_constructor.hpp 24 1 xml However, I am bumping into C2139, above. Is there any way for variant to work with forward declared structs (or classes, etc)? Or am I just asking too much from C++? I am building against Visual Studio 2013, Boost 1.55. Thank you... Best regards, Michael Powell

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boost::lockfree::queue not working with -fgnu-tm
by Philipp Schoppe 18 Jul '14

18 Jul '14

Hello, I try to benchmark different queue implementations. I have a test program which includes the boost lockfree queue and some custom implementations where one is using gcc's STM. In order to compile it, I need to add the -fgnu-tm flag. I am using an up-to-date arch linux system with gcc 4.9.0 and boost 1.55.0 When adding this flag, I get a compilation error. This is a small example that illustrates the problem: errtest.cpp: #include <boost/lockfree/queue.hpp> int main () { boost::lockfree::queue<int> lfqueue; lfqueue.push(234); return 0; } Compiling it using g++ -std=c++11 -lboost_system -g -O3 -Wall -Werror -Wswitch-enum -fgnu-tm errtest.cpp -o test leads to an error.

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[Log] Extract severity value
by Olivier Tournaire 17 Jul '14

17 Jul '14

Hi all, I am trying to extract severity level from a log record, but i seems that I am doing it the wrong way. Here is the code I use: void LogDockWidget::receiveLog(boost::log::record_view const& rec, const std::string& log) { logging::value_ref< logging::trivial::severity_level > level = logging::extract< logging::trivial::severity_level >("Severity", rec); // ... } Here level.get() always returns "info". All my logs are done with the BOOST_LOG_TRIVIAL(...) macro. The formatter whereas displays correctly the severity level. Here is how it is defined: void LogDockWidget::init_logging() { boost::shared_ptr< logging::core > core = logging::core::get(); typedef sinks::synchronous_sink< QTextEditFormattedSinkBackend > sink_t; boost::shared_ptr< sink_t > sink(new sink_t); // ... logging::add_file_log( keywords::file_name = logFilename, keywords::auto_flush = true, keywords::format = ( BUILD_LOG_FORMATTER() ) ); sink->set_formatter( BUILD_LOG_FORMATTER() ); core->add_sink(sink); // Add attributes that we will use logging::add_common_attributes(); core->add_global_attribute( "ThreadID", attrs::current_thread_id()); } #define BUILD_LOG_FORMATTER() \ expr::stream \ << "[" << expr::format_date_time< boost::posix_time::ptime >("TimeStamp", "%Y-%m-%d %H:%M:%S") << "] " \ << expr::attr<unsigned int>("LineID") << " " \ << ": <" << logging::trivial::severity << "> " \ << " [" << expr::attr<attrs::current_thread_id::value_type>("ThreadID") << "] " \ << expr::if_(expr::has_attr(scope_attribute)) \ [ \ expr::stream << "[" << scope_attribute << "] " \ ] \ << expr::message Could you please let me know what I am doing wrong? Regards, Olivier

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Re: [Boost-users] Intrusive: Checking for undefined behaviour
by Brian Wood 16 Jul '14

16 Jul '14

Ion Gazta?aga writes: >El 15/07/2014 5:33, Brian Wood escribi?: >> I was reading here about some of the sanitizers >> >> http://cplusplusmusings.wordpress.com/ >> >> and decided to try it out the undefined behavior >> sanitizer on some code. One thing that came >> out was related to the Intrusive library. > > Can you try with the release candidate (http://boost.cowic.de/rc/) for > Boost 1.56? I solved some undefined behaviour issues recently but I > don't know if this is one of them. I tested it with 1.56 now and the sanitizer is no longer reporting a problem with Intrusive. It looks like whatever you did has helped. I appreciate your being on top of this. -- Brian Ebenezer Enterprises - "Let a man so consider us, as servants of Messiah and stewards of the mysteries of G-d." First Corinthians 4 http://webEbenezer.net

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