Re: [boost] ublas: matrix views

From: Kresimir Fresl (fresl_at_[hidden])
Date: 2002-04-16 04:24:21

Toon Knapen wrote:

> I'm looking for taking a view of a ublas matrix. What I mean is soth like :
> matrix< double > a(10,10);
> size_t row_indices[] = { 0, 3, 4, 9 };
> size_t column_indices[] = { 2, 3, 7 };
> matrix_view< matrix< double > > view( a, 
>                                       row_indices, row_indices + 4,
>                                       column_indices, column_indices + 3 )
> 
> 
> to give me a 4*3 alias to the original matrix containing rows 0,3,4,9 and 
> columns 2,3,7. Thus view(0,0) == a(0,2)
> 
> AFAIK soth similar is not possible at the moment (if it is, please let me 
> know) so I guess I'll give it a shot to implement it in ublas.

I am very interested in this functionality, so, yes, shoot ;o)

Since Joerg didn't reply, I will quote his earlier comment
on this topic (thread: `slicing and ranges of matrices', Jan.  24th):

``I believe, that it's difficult to estimate the complexity of
operations on such a view for sparse matrices (in other words: they
could be rather inefficient). May be we currently should be more
interested in some gather and scatter functionality for sparse
matrices.''

Sincerely,

fres