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
>
>
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