[Boost-bugs] [Boost C++ Libraries] #4034: better vector/matrix assignment (or initialization)

Subject: [Boost-bugs] [Boost C++ Libraries] #4034: better vector/matrix assignment (or initialization)
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-03-22 21:57:50

#4034: better vector/matrix assignment (or initialization)
------------------------------+---------------------------------------------
 Reporter:  guwi17            |       Owner:  guwi17      
     Type:  Patches           |      Status:  new         
Milestone:  To Be Determined  |   Component:  uBLAS       
  Version:  Boost 1.42.0      |    Severity:  Optimization
 Keywords:  assigment         |  
------------------------------+---------------------------------------------
 proposal from Nasos Iliopoulos:

 I suppose many of you miss the functionality of creating certain matrices
 or vectors as in plain c:

 double vec[] = {0.1, 2.0, 5.0. 0.3}

 With the proposed classes (in the attached file) it is possible to fill
 vectors and matrices like that:
 {{{
 vector<double> vec(3);
 vec << 1.0, 2.0, 3.0;
 }}}
 {{{
 vector_range<vector<double> > vr (a, range (1, 3));
 vr << 11.0, 12.0;
 }}}
 {{{
 matrix<double> mat(3,3);
 mat << 1.0, 2.0, 3.0,
        4.0, 5.0, 6.0,
        7.0, 8.0, 9.0;
 }}}
 or even:
 {{{
 mat << 1.0, 2.0, 3.0,
        vec,
        7.0, 8.0, 9.0;
 }}}
 you can also use this form:
 {{{
 vector<double> vec(10);
 vec << 1.0 , project(a, range(0,2)), 10.0, 11.0, a, 15.0, 16.0;
 }}}

 Another nice trick that is especially useful for sparse matrices and
 vectors is:
 {{{
 compressed_matrix<double> cm(3,4, 3*4);
  cm <<  non_vector(4),
         1.0, 2.0, project(a,range(0,2)),
         non_vector(3),2;
 }}}
 where the non_vector free functions returns a "non vector" object that is
 used to traverse the expression without modifying it.


 I would appreciate your general feedback, thoughts, critisism as well as
 your opinion in the following issues:

 - Are there any features beside those presented above and in the attached
 example that you probably would like to see?
 [[BR]]
 - Where do you think this should be added? As a separate header file, or
 included in vector_ and matrix_ expression headers?
 [[BR]]
 - I found it incovenient to implement this functionallity using iterators
 (especially when the functions work on sparse types). Does anybody think
 there are considerable gains if attempting that?
 [[BR]]
 - I also consider implementing functionality so that project(a, range(..))
 << ...; is possible, but I initially faced some problems. I think that
 _range and _slice classes need to include an operator<< in order for this
 to work. If somebody wants to work on that it would be great.
 [[BR]]
 I will write the unit tests if the maintainers consider the proposed code
 for addition into uBlas.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4034>
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