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Invoking 'brent_find_minima' for a member function of a class?
by s seelenluft 22 Jul '09

22 Jul '09

Hi, I found this example: http://net.pku.edu.cn/~webg/src/paradise/thirdparty/installed/include/boost… works fine but I have trouble figuring out how to adapt this if the function to minimize is a member function of a class (and invoked in another member function). Any example of how to call brent_find_minima (or similar functions) from a member function and minimizing a member function would be very welcome. I have to the advice to wrap the function to be minimized into a static wrapper function but could not find an example how to do this from within a member function (I have it working when calling from main). Thanks. Markus

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Iterator to wrap around ends of the container. Does it exist?
by PB 22 Jul '09

22 Jul '09

Hi, Just wondered if there was anything in Boost so that when an iterator is incremented, if it's at the last element it goes to the begin() of the container. And for decrement if at the beginning it would refer to one before end(). The sequence would have to be finite, so just selecting a different logical begin and end really. I'm looking to solve this using some kind of new iterator (iterator adaptor) rather than a change of container. If there anything in Boost for this? Thanks, Pete

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Variance calcs in the stats library and in Excel
by Archie14 22 Jul '09

22 Jul '09

In the docs (file:///C:/Libraries/boost/boost_1_39_0/doc/html/accumulators/user_s_guide.htm l#accumulators.user_s_guide.the_statistical_accumulators_library.variance) there is an example of calculating variance of values 1,2,3,4,5 accumulator_set<int, stats<tag::variance(lazy)> > acc1; acc1(1); acc1(2); acc1(3); acc1(4); acc1(5); BOOST_CHECK_EQUAL(5u, count(acc1)); BOOST_CHECK_CLOSE(3., mean(acc1), 1e-5); BOOST_CHECK_CLOSE(11., moment<2>(acc1), 1e-5); BOOST_CHECK_CLOSE(2., variance(acc1), 1e-5); When I am doing the same in Excel the mean is indeed 3, which matches the example, but variance is 2.5 and not 2. I am using AVERAGE and VAR formulas in Excel for mean and variance respectively Why there is a mismatch between variance values??

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Re: [Boost-users] where is the pdf documentation?
by Tan, Tom (Shanghai) 22 Jul '09

22 Jul '09

http://boost.cowic.de/rc/pdf/ > ??? I see mention of pdf documentation, but couldn't find it online. > Can someone give the link to it?

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[math] finding c such that w1/c+...+wn/c < math::tools::max_value<T>()
by er 21 Jul '09

21 Jul '09

Hi All, A little while back the following code was suggested to find c such that (x/c)+(y/c) <= C = math::tools::max_value<T>() template<class T>// static T scale_to_max( const T& x, const T& y ) { double max = (std::numeric_limits<T>::max)(); if(x > max - y) { double c = x/max + y/max; while(!boost::math::isinf(x/c + y/c)) { c = boost::math::float_prior(c); } while(boost::math::isinf(x/c + y/c)) { c = boost::math::float_next(c); } return(c); } else { return(static_cast<T>(1)); } } I'm now trying to generalize this i.e. find c such that w1/c+...+wn/c <= C: 1) split w1,..,wn into maximal size, sum less than C, subgroups. 2) apply scale_to_max iteratively over adjacent groups. This does not always suceed (see example at the bottom). Any suggestion would be appreciated. *.hpp template<typename T> class scale_sum_to_max{ public: typedef void result_type; typedef T argument_type; scale_sum_to_max(T cum_sum):cum_sum_(cum_sum),c_(static_cast<T>(1)){} scale_sum_to_max():cum_sum_(static_cast<T>(0)),c_(static_cast<T>(1)){} void operator()(T x){ if( math::isinf(scaled_sum()+(x/c_)) ){ T s = scale_to_max( scaled_sum(), x/c_ ); cum_sum_ /= s; c_ *= s; BOOST_ASSERT(!math::isinf(cum_sum_+x/c_)); } cum_sum_ += x/c_; } T scaling_factor()const{ return c_; } T scaled_sum()const{ return cum_sum_; } private: T cum_sum_; T c_; }; template<typename T> class finite_sums{ typedef std::vector<T> cont_t; public: typedef void result_type; typedef T argument_type; finite_sums() { coll_.push_back(static_cast<T>(0)); } void operator()(T x){ if(math::isinf(sum()+x)){ coll_.push_back(x); }else{ coll_.back() += x; } } const cont_t& collected()const{ return coll_; } T scaling_factor()const{ return for_each( begin(coll_), end(coll_), scale_sum_to_max<T>() ).scaling_factor(); } private: T sum()const{ return coll_.back(); } cont_t coll_; }; }} *.cpp typedef double value_t; typedef std::vector<value_t> vec_t; const unsigned n = 1e5; //n = 1e3 OK value_t w = math::tools::max_value<value_t>(); w /= 2; vec_t vec_w(n,w); value_t scaling_factor = for_each( begin(vec_w), end(vec_w), math_limit::finite_sums<value_t>() ).scaling_factor(); //assertion failed: (!math::isinf(cum_sum_+x/c_))

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asio: transporting exceptions across threads
by Zachary Turner 21 Jul '09

21 Jul '09

Suppose I have some io_service object in which I call run() from thread A. Thread A is the main controller of the i/o operations and does things like issuing reads and, upon completion, issuing writes for those reads. The writing service might wish to spawn off some child services that runs in thread B. So when thread A says writer.async_write_data() all it really does is call child_writer_service.post() with the data. Supposing an exception occurs in thread B, what is the best way to have this terminate the entire asio pipeline and propagate the exception all the way up to outside of thread A's call to io_service::run()? I've looked at the sample code on the boost::exception tutorial but I'm unable to apply this to the situation in asio, either due to differences in the threading model or due to my own misunderstandings. Thanks

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where is the pdf documentation?
by Ozgur Ozturk 21 Jul '09

21 Jul '09

Hi, I see mention of pdf documentation, but couldn't find it online. Can someone give the link to it? Thanks, Best regards, Ozgur (Oscar) Ozturk www.DrOzturk.com Phone: +1 (908) DROZGUR i.e, +1 (908) 376-9487

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usage of boost::asio::async_write and boost::asio::buffer
by Ozgur Ozturk 21 Jul '09

21 Jul '09

Hi, I am modifying example echo server for my server. I started to get the attached error, and I suspect I am using buffer incorrectly since error started after a change there. I just changed a line from boost::asio::async_write(socket_, boost::asio::buffer("1^", 3, boost::bind(&session::handle_write, this, boost::asio::placeholders::error)); to boost::asio::async_write(socket_, boost::asio::buffer(replyString, replyString.size()), boost::bind(&session::handle_write, this, boost::asio::placeholders::error)); I generate the replyString to have results from my database query separated with ^ signs (which is used to tokenize the replyString on the client side...) string replyString="1^"; while(res->next()) { replyString+=res->getString("nickname")+"^"; } I checked that replyString.size() is really one more than the final filled position index in replyString. Any ideas, suggestions? TIA, Best regards, Ozgur (Oscar) Ozturk www.DrOzturk.com Phone: +1 (908) DROZGUR i.e, +1 (908) 376-9487

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Docs missing info about which headers to include?
by Jason Cipriani 21 Jul '09

21 Jul '09

I'm new to much of boost. It is less than ideal to have to search through boost headers to find which ones to include for a class (e.g. boost::scoped_lock). Where can I find information about which headers the classes are in? It does not seem to be in the documentation, e.g.: http://www.boost.org/doc/libs/1_37_0/doc/html/boost/interprocess/scoped_loc… This is strange to me, since this type of info is pretty fundamental. In that particular case, after trying boost/thread/scoped_lock.hpp and boost/interprocess/scoped_lock.hpp, I resorted to searching through files and eventually found it in boost/interprocess/sync/scoped_lock.hpp (among other locations, but that one seems to be the most reasonable). Is there some place in the boost docs where I can find what headers to include to use the classes? Thanks, Jason

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Re: [Boost-users] Spirit 1.39 compilation times (avi)
by Avi Bahra 21 Jul '09

21 Jul '09

Can someone explain why the compilation times are faster under Spirit2.1 I have noticed that even boost 1.39 references spirit qi, can I assume that faster compile times are due to moving from spirit classic to spirit qi ? More importantly can we intermix classic and qi grammars, if not are there any migration notes, to help users -- Best regards, Ta, Avi

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