July 2011 - Boost-users - lists.preview.boost.org

[multi_array] operator= requires resize - why?
by Markus Werle 04 Jun '12

04 Jun '12

Hi! IMHO the behaviour of operator= for multi_array is a little bit broken. A lot of preconditions required: template <typename ConstMultiArray> multi_array_ref& operator=(const ConstMultiArray& other) { [...] // make sure the dimensions agree assert(other.num_dimensions() == this->num_dimensions()); assert(std::equal(other.shape(),other.shape()+this->num_dimensions(), this->shape())); Besides the fact that I get mad about asserts instead of exceptions (please change this to a way users may choose) why do we have such an odd behaviour here? >From page 1, line 3 of the docs I cite: "The interface design is in line with the precedent set by the C++ Standard Library containers" - this is not true for operator=, since std::<container>::operator= works fine for me all the time _without_ any resize. Could we please change the behaviour of multi_array::operator= to take care of resize where in need to? IMHO operator= should result in a true copy ignoring previous state. Markus

6 18

offlist - Re: [iterator] Problems with iterator_facade and const-qualification
by Neil Groves 24 May '12

24 May '12

On Sat, May 7, 2011 at 5:52 PM, Dave Abrahams <dave(a)boostpro.com> wrote: > On Fri, May 6, 2011 at 1:51 PM, Evan Driscoll <driscoll(a)cs.wisc.edu> > wrote: > > On 05/06/2011 11:59 AM, Jeff Flinn wrote: > >> > >> You might google any_iterator, and see how other authors have addressed > >> similar problems. > > > > Great! I tried to find someone who had done something similar, figuring I > > couldn't have been the first, but all the search terms I tried were too > > generic. > > > > Thanks, > > Evan > > You can find one in the ASL that's built on iterator_facade. > http://stlab.adobe.com/classadobe_1_1any__iterator.html > > The underlying Boost.Range implementation implements an any_iterator that I believe to be similar to the one in ASL in terms of functionality. I believe that the small-buffer optimization implementation is superior to forcing the definition of a closed-set of possible type as suggested in a TODO within the ASL documentation. During my performance testing I had considerably superior performance than the ASL implementation. I wondered if you disliked my implementation, or had any feedback. Additionally I wondered what you thought about moving the Boost.Range internal any_iterator implementation into Boost.Iterator. I can't honestly imagine a good use-case for using any_iterator in preference to any_range, hence I haven't suggested this previously. This could easily be due to my lack of imagination! Can you think of a time when using an any_iterator on any interface would be superior to using an any_range? Your opinions and guidance would be much appreciated. HTH, > > -- > Dave Abrahams > BoostPro Computing > http://www.boostpro.com Regards, Neil Groves

4 5

Recommended mock framework to use with Boost?
by doug livesey 15 Mar '12

15 Mar '12

Hi -- I'm trying to learn to develop properly with C++ and Boost, and to that end am learning along with Boost.Test, as I'm a BDD coder in another language (Ruby) in my day job. I'm at the point, now, where my tests could really benefit from a mocking framework. There doesn't appear to be one in Boost (not documented, at least), so I wondered if anyone on the list could recommend a mocking framework that they use that works well with Boost.Test? Any and all advice gratefully received, Doug.

9 16

Boost.Generic sources?
by Nathan Ridge 05 Mar '12

05 Mar '12

I just read about the Boost.Generic library at https://github.com/boostcon/2011_presentations/raw/master/thu/Boost.Generic…. It looks amazing! I understand it's not fully complete, but are the sources available somewhere? Thanks, Nate.

2 5

[python] converting C++ object to PyObject
by Johan Råde 05 Dec '11

05 Dec '11

I have three C++ classes X, Y and Z that I have exported from C++ to Python using python::class_. Now I want to write a factory function like PyObject* f(char c) { if(c == 'x') return new X; else if(c == 'y') return new Y; else if(c == 'z') return new Z; else PyErr_SetString(PyExc_ValueError, "Bad function argument"); } and export that function to Python. What is missing here is code that converts X*, Y* and Z* to PyObject*. How do I write that? Thank you, Johan

4 7

Manipulating boost::multi_array
by kelvSYC 30 Nov '11

30 Nov '11

Right now, I'm using boost::multi_array for implementing a dynamic-sized matrix for an algorithm in which the number of rows and columns therein may wildly fluctuate (is boost::multi_array even the right class for this?). What's frustrating me is how I can do any and all of the following: 1. Remove a single row or column from a matrix 2. Insert a single row or column to a matrix 3. Augment two matrices together 4. Swap two rows or columns Is there any way to do the first three without calling resize() and moving the elements around manually? For the last, does something like std::swap(A[row1], A[row2]) work?

3 3

multi-array and pdes
by petros 07 Nov '11

07 Nov '11

Hi, These can very well be very naive questions, since I am relatively new to this - apologies..: I am trying to write a pde solver for a 3D problem. Multi-array seems like a very natural choice for a data structure to store the functtion values. The method I am trying to use is operrator splitting. This amounts to solving a tridiagonal system for each dimension in sequence. Suppose then that I have a MA( M, N, L ): It is highly desirable to maintain this xyz (let's call it) "logical" system of reference since incorporation of boundary conditions and stencil calculations would be conceptually straightforward -otherwise very complicated. The idea being that, I would then have the tridiagonal opertator ( and rhs) in the "rotated" system and all other calculations in the "logical" one. Therefore, I need some fascility to rotate my MA, from the xyz to yzx etc (cyclically). Is there functionality ( as a view to the data ) that would allow me to do this off-the-shelve? Also, a couple of other points: -If I wanted to use views to subgrids, in parallelized calculations, are there memory allocations that happen under the hood for which I should worry (for performance)? -Is a one dimensional MA usable? -Are there adapters between 2D MAs and uBlas matrices? Thank you very much for your help in advance! P-

4 21

Compilation Error in Boost::unordered_detail::hash_table on boost 1_46_1
by Shinil Gangadharan 27 Sep '11

27 Sep '11

Hi, I am using Sun CC v5.9 compiler to compile boost 1_46_1. We are getting the following error. Is there a way to get around with this error? "/dvobs/a-ThirdParty/Boost/boost_1_46_1/boost/unordered/detail/table.hpp", line 595: Error: Could not find a match for boost::unordered_detail::hash_table<boost::unordered_detail::T>::find(const boost::unordered_detail::Key&, const boost::unordered_detail::Hash&, const boost::unordered_detail::Pred&) const. "/dvobs/a-ThirdParty/Boost/boost_1_46_1/boost/unordered/detail/table.hpp", line 595: Error: Too many args in template, from boost::unordered_detail::Hash on ignored. Regards, Shinil V.G.

3 2

[BGL] Distributed adiacency_list memory allocation
by Cosimo Calabrese 27 Sep '11

27 Sep '11

Hi to all, I'm working on WinXP, VS2010, Boost 1.46.1. I've writed this short program: //---------------------------------- #include <boost/graph/use_mpi.hpp> #include <boost/graph/distributed/mpi_process_group.hpp> #include <boost/graph/distributed/adjacency_list.hpp> using boost::graph::distributed::mpi_process_group; typedef boost::property<boost::vertex_distance_t, long, boost::property<boost::vertex_name_t, std::string > > vertex_prop; typedef boost::property<boost::edge_weight_t, long > edge_prop; typedef boost::adjacency_list< boost::vecS, boost::distributedS<mpi_process_group, boost::vecS>, boost::directedS, vertex_prop, edge_prop > Graph; typedef boost::graph_traits<Graph>::edge_descriptor EdgeDescriptor; typedef boost::graph_traits<Graph>::vertex_descriptor VertexDescriptor; int main(int argc, char* argv[]) { boost::mpi::environment env(argc,argv); Graph g( 10 ); return 0; } //---------------------------------- When I launch it, every process allocates about 1 GB of memory. Why it allocates all that memory? Is it normal? Is there any tuning to the PBGL framework that I must made? I use it on a 2-core machine, and the command that I use is: mpiexec -n 2 .\test.exe I've tried with openMPI 1.4.3 and Microsoft HPC Pack 2008, but it seems irrilevant. Thanks in advance, Cosimo Calabrese.

5 8

trouble with boost/random/poisson_distribution and large lambda
by Michael King 30 Aug '11

30 Aug '11

Hello, I am new to the boost mailing list, so I apologize before hand if this is not the appropriate forum for this question. I have been using boost/random recently and have encountered what appears to be a problem with poisson variate generators with large lambda values. The random values can't seem to get much higher than 800 regardless of what value lambda is. For example: #include<iostream> #include<iterator> #include<vector> #include<algorithm> #include<boost/random/poisson_distribution.hpp> #include<boost/random/variate_generator.hpp> #include<boost/random/mersenne_twister.hpp> using namespace boost; using namespace std; int main() { mt19937 gen; double lambda = 1000.; poisson_distribution<int, double> pois(lambda); variate_generator<mt19937&, poisson_distribution<int, double> > rpois(gen, pois); // generate 10 random poisson variables vector<double> sample(10); generate(sample.begin(), sample.end(), rpois); cout << "Simulating from Poisson Random Variable with lambda=" << lambda << endl; cout << "\nSample: "; copy(sample.begin(), sample.end(), ostream_iterator<int>(cout, " ")); cout << "\n\nShouldn't the numbers be a little closer to 1,000?" << endl; return 0; } Thanks, Mike

2 1