Re: [ublas] submatrix with indexvector

Subject: Re: [ublas] submatrix with indexvector
From: Philipp Kraus (philipp.kraus_at_[hidden])
Date: 2010-07-23 16:40:35

Hi Ralf,

thanks for the tip. Can I convert a ublas::vector<std::size_t> direct 
to the indirect_array
or should I copy element by element?

Thanks

Phil

On 2010-07-23 08:48:08 +0200, Ralf Denzer said:

> Hallo Philipp, 
> 
> yes, something very similar works: 
> Please check  indirect_array<> in ublas/storage.hpp
> It's not well documented, but works since long time.
> 
> Something like the following should work: 
> 
> //----------------------------
> namespace ublas = boost::numeric::ublas;
> 
> const unsigned N = 7;
> ublas::matrix<int> A(N,N);
> ublas::vector<int> V(N);
> 
> ... fill matrix A and vector V here ...
> 
> // define an indirect_array
> const unsigned n = 3;
> ublas::indirect_array<> ia(n);
> ia[0] = 1;
> ia[1] = 2;
> ia[2] = 4;
> 
> // ia(n) to extract some indices
> ublas::matrix_indirect<ublas::matrix<int> > Mindirect(M, ia,ia);
> std::cout << "Mindirect=\n" << Mindirect << std::endl;
> 
> // or use ublas::project
> std::cout << "Mprojected=\n" << ublas::project(M, ia, ia) << std::endl;
> 
> // similar for vectors
> ublas::vector_indirect<ublas::vector<int> > Vindirect(V,ia);
> std::cout << "Vindirect=\n" << Vindirect << std::endl;
> 
> // and
> std::cout << "Vprojected=\n" << ublas::project(V, ia) << std::endl;
> 
> //----------------------------
> 
> Thus, with 'ublas::indirect_array<> indexvector' you should be able 
> to peform exactly your operation 
> 
> project(x, indexvector, indexvector) += other matrix with 
> indexvector.size x indexvector.size
> 
> Bye 
> 
> Ralf 
> 
> PS: Thanks to David, at least ublas::matrix_indirect and ublas::vector_indirect
> is now a bit documented. See http://ublas.sourceforge.net/refdoc/
> 
> 
>  Hello, 
> 
> can I extract a submatrix from a ublas::matrix with an indexvector? 
> I've got a ublas::vector with index values and a 
> ublas::matrix(1000,1000). The indexvector holds only 12 index position 
> and I need something like: 
> 
> ublas::matrix x(1000,1000); 
> project(x, indexvector, indexvector) += other matrix with 
> indexvector.size x indexvector.size 
> 
> I must cut a submatrix which is not continously and adds another 
> matrix.  Are there any boost operations or should I run over all 
> elements? 
> 
> Thanks 
> 
> Phil
>   
> 
> <image>
> Neu: WEB.DE De-Mail - Einfach wie E-Mail, sicher wie ein Brief!    
> Jetzt De-Mail-Adresse reservieren: https://produkte.web.de/go/demail02
> _______________________________________________
> ublas mailing list
> ublas_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/ublas
> Sent to: gclbu-ublas-dev-3_at_[hidden]