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Ublas : |
From: Epic John (epicjohn_at_[hidden])
Date: 2006-12-01 02:11:07
Allowing the selection of arbitrary (ordered) sets (or even bags) of rows
and columns, would be a great feature, and hopefully makes it to ublas
someday.
John
On 11/27/06, Gunter Winkler <guwi17_at_[hidden]> wrote:
>
> Am Samstag, 25. November 2006 11:55 schrieb Giuseppe Bilotta:
>
> > Neither range nor slice can give me this, although I could use four
> > ranges and assemble the submatrix this way. However, this is overkill
> > (and slow) when all I need it for is a comfortable (templatable via
> > matrix_expression) way to access "all but" certain rows/columns of a
> > matrix.
>
> There is no matrix proxy with such a functionality in ublas. I suggest
> the following procedure:
>
> // untested, should work with ublas::range, ublas::slice,
> // std::set<int> (or any sorted list of integers)
> template < class MATRIX, class RANGE >
> void foo(const MATRIX & A, RANGE & r)
> {
> typename MATRIX::const_iterator1 it = A.begin1();
> typename MATRIX::const_iterator1 it_end = A.end1();
> typename RANGE::const_iterator ex = r.begin();
> typename RANGE::const_iterator ex_end = r.end();
> for ( ; it != it_end ; ++it) {
> while ( it != it_end && ex != ex_end && it.index1() >= (*ex)) {
> if (it.index1() == (*ex)) { ++it; }
> ++ex;
> }
> // do something with it.begin() ... it.end()
> }
> }
>
> > Essentially, what I need is a "range complement" proxy, although I
> > would only use it with single rows and columns. Would it be hard to
> > implement? I'm a little daunted by the complexity of the uBLAS
> > internals ...
>
> Implementing this would mean to copy the matrix_range class and rewrite
> the iterators (and some other functions that return size and similar
> data). You can even try to unify matrix_range and matrix_slice into a
> general submatrix proxy that accepts arbitrary lists of rows and cols.
> The main work is to do a good iterator implementation.
>
> mfg
> Gunter
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