Re: [ublas] Boost FOREACH matrix iterator examples?

Subject: Re: [ublas] Boost FOREACH matrix iterator examples?
From: Joaquim Duran (jduran.gm_at_[hidden])
Date: 2013-10-06 17:15:09

Hello,

Few days ago, I pulled a change to the ublas repository (in github) about a
vector facade for the matrices. With these changes you can iterate the
matrices like a vector of rows or a vector of columns. With these facades
you can use the BOOST_FOREACH.

Joaquim Duran

2013/10/4 Reich, Darrell <DARRELL.REICH_at_[hidden]>

> The two pieces of code below attempt to iterate over the non zero elements
> of a matrix, both crash. I suspect from looking over the various
> discussions online that the correct placement of & is critical? Assuming it
> is possible to create two working examples of BOOST_FOREACH matrix and
> matrix iterators, which method is preferred / “better” / more efficient?
> Thanks!****
>
> ** **
>
> #include <boost/foreach.hpp>****
>
> #include <boost/numeric/ublas/matrix.hpp>****
>
> #include <boost/numeric/ublas/matrix_sparse.hpp>****
>
> #include <boost/numeric/ublas/matrix_expression.hpp>****
>
> #include <boost/numeric/ublas/matrix_proxy.hpp>****
>
> #include <boost/numeric/ublas/vector.hpp>****
>
> #include <boost/numeric/ublas/vector_sparse.hpp>****
>
> #include <boost/numeric/ublas/vector_expression.hpp>****
>
> #include <boost/numeric/ublas/vector_proxy.hpp>****
>
> ** **
>
> boost::numeric::ublas::compressed_matrix<float> M(n,n);****
>
> boost::numeric::ublas::compressed_vector<float> v(n);****
>
> ** **
>
> // Example 1: BOOST for each…****
>
> // TODO: 2D nested matrix example?****
>
> BOOST_FOREACH(float, v)****
>
> {****
>
>    v += 1; // do something with each non zero element of v…****
>
> } // end for each****
>
> ** **
>
> // Example 2: iterators****
>
> boost::numeric::ublas::compressed_matrix<u32>::iterator1 i;****
>
> boost::numeric::ublas::compressed_matrix<u32>::iterator2 j;****
>
> for (i = M.begin1(); i != M.end1(); ++i)****
>
> {****
>
>    for (j = M.begin2(); j != M.end2(); ++j)****
>
>    {****
>
>       // use j.index1(), j.index2(), *j to access each non zero element of
> M****
>
>       *j = v(j.index1()); // do something with each non zero element of
> both matrix and vector…****
>
>    } // end for****
>
> } // end for****
>
> ** **
>
> Extra credit: I suspect I should protect the code with some kind of assert
> to ensure the size of vector is the same as the size of matrix.****
>
> ** **
>
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