Re: [Viennacl-support] Is there column wise access functionality of matrices available in ViennaCL

[Karl R. <ru...@iu...>]

Hi Omar,

we are currently working on porting the convenience layer from ublas 
such that rows and/or columns of a dense matrix can be directly 
manipulated like a vector.

You can use matrix_range<> and project() in the meanwhile for submatrix 
manipulation as a workaround:

  matrix<double> A(size, 3);
  range all_rows(0, size);
  range col_0(0, 1);

  matrix<double> C = viennacl::linalg::prod(
                       trans(project(A, all_rows, col_0)),
                       project(A, all_rows, col_0)
                                           );
  std::cout << "Squared norm of first column of A: "
            << C(0,0) << std::endl;

This approach won't give you the best performance, though...

Best regards,
Karli


On 07/23/2012 04:11 PM, Omar Valerio wrote:
> Hi list,
>
> I'm trying to figure out how to use ViennaCL in my project.  My project
> use Eigen and now I want to get some extra performance.  My program used
> an STL vector of Eigen Vector3d.
>
> I thought about using a vector of a non scalar type (a vector of
> vectors). I realized ViennaCL such an approach is not convenient for
> parallelization and now I am packaging the vectors into a matrix. This
> works for me for example to perform vector substraction but I am
> concerned about other vector operations I have in my code.
>
> In Eigen there is a row wise operator that allow me to affect individual
> rows within the matrix, I want to ask if there is such a thing also in
> ViennaCL.. My use case is very simple.  I have a matrix composed of
> vector positions organized in rows/colums.   I want to be able to
> compute squared norms for those vectors..  In Eigen  I will do this as
> follows:
>
> vectorSqNorm = Matrix.cwise().abs2();  // abs2  is square of the
> absolute value
>
> Thanks,
> --
> Omar V.M.
>
>
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