----- Original Message ----- From: vladimir josef sykora To: boost-users@yahoogroups.com Sent: Wednesday, March 26, 2003 11:25 AM Subject: [Boost-Users] [uBLAS] operations thoughts
Hello, Had a quick look into uBLAS library, and noted the incompatibility between std::vector<> and ublas' binary operations. For example, I have an ublas::matrix<> and wanted to multiply it by a std::vector<>.
I'd tend to recommend to use ublas::vector<> instead for the basic linear algebra. One can use std::vector as ublas::vector's storage container if needed.
Since _all_ of ublas data containers provide iterators, I'm wondering why the library doesn't provide algorithms that work on iterators?
Because the signatures of the algorithms are more complex then.
In this way data structures and operators will be decoupled.
Container and operators are decoupled through proxies (views?) like vector_range<> and matrix_range<>. One could imagine these as tuples of iterators.
For example, to do the product between a matrix and a vector:
********* untested code ********* template <class MatrixRowIterator, class MatrixColIterator, class InputIterator, class OutputIterator> OutputIterator prod(MatrixRowIterator first_row, MatrixRowIterator last_row, MatrixColIterator, InputIterator first_vec, OutputIterator result) { InputIterator cp_first=first_vec; while(first_row!=last_row) { typename MatrixRowIterator::value_type val(0); MatrixColIterator first_col, last_col; first_col=first_row.begin(); last_col=first_row.end(); while(first_col!=last_col) val+= *first_col++ * *first_vec++; *result++ = val; ++first_row; first_vec=cp_first; } return result; }
I'd write this kind of code, if I'd have to implement new algorithms.
// user side : prod(umatrix.begin1(), umatrix.end1(), umatrix.begin2(), std_vector.begin(), std::back_inserter(std_vector_result));
This of course with the respective preconditions.
Also, wouldn't be a good idea to provide copy c'tor and operators accepting std::vector<> for the ublas::vector<> ?
I'll have to think about it. Thanks, Joerg