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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