
Ublas : 
Subject: [ublas] Assignement operation proposal.
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 20100321 15:45:57
Dear all,
I would like to propose the following for addition into uBlas.
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}
and are forced to element wise define it in ublas with:
vec(0) = 0.1;
vec(1) = 2.0;
....
Insipired by the fucntionality of boost.assignment, i decided to implement something similar in ublas. Unfortunately due to the special way ublas is handling its containers I did not find it that convenient to use boost.assignment.
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?
 Where do you think this should be added? As a separate header file, or included in vector_ and matrix_ expression headers?
 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?
 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.
I will write the unit tests if the maintainers consider the proposed code for addition into uBlas.
Best Regards
Nasos Iliopoulos
_________________________________________________________________
Hotmail: Trusted email with powerful SPAM protection.
http://clk.atdmt.com/GBL/go/210850553/direct/01/