Re: [ublas] returning a ublas matrix from a function

Subject: Re: [ublas] returning a ublas matrix from a function
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2014-08-05 10:03:02

Sannan,
prior to diving in ublas I would suggest spending some time learning 
C++, since it is not a trivial language. As long as you have some 
programming experience a good introductory book would be "Accelerated 
C++ by Koening and Moo".

Anyway If you are using a C++11 compiler this will work and is 
preferable from the C array (please note that there are a few 
performance improvements that might take place here):
[for gcc compile with: g++ main.cpp -o myprog -std=c++11]

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>
#include <array>

using namespace boost;
using namespace boost::numeric::ublas;

typedef boost::numeric::ublas::matrix<double> BMT;

std::array<BMT, 3> fun(int w,int h)
{
     std::array<BMT, 3> M ={
         scalar_matrix<double>(w, h),
         scalar_matrix<double>(2*w, h),
         scalar_matrix<double>(3*w, h)
     };

     return M;
}

int main()
{

     unsigned w,h;
     w = 3;
     h = 3;

     auto matrices = fun( w, h);

     std::cout << matrices[0] << std::endl;
     std::cout << matrices[1] << std::endl;
     std::cout << matrices[2] << std::endl;

     return 0;
}

Best,
Nasos

On 08/05/2014 09:00 AM, sanann wrote:
> The basic thing that i want to do is
> 1. have a bunch of matrices either in a function or in a class.
> 2. these would be manipulated and the output needs to be returned inorder to
> use it for further manipulation.
> 3. so assign 3 matrices into an array.
> 4. now th problem i face is using this array in an external code.
>
> for example.
>
> #include <boost/numeric/ublas/matrix.hpp>
> #include <boost/numeric/ublas/io.hpp>
>
> using namespace boost;
> using namespace boost::numeric::ublas;
>
>
> typedef boost::numeric::ublas::matrix<double> BMT;
>
> BMT fun(int w,int h)
>    {
>
>      BMT M[3]=
>            {
>          scalar_matrix<double>(w, h),
>          scalar_matrix<double>(w, h),
>          scalar_matrix<double>(w, h)
>      };
>      std::cout<<M[0]<<std::endl;
>    return M[0];
>    }
>
> here i want to have all the matrices stored in array M how do i do that?
>
> int main()
> {
>
>      unsigned w,h;
>      w = 3;
>      h = 3;
>
>      fun(w,h);
>
>      std::cout<<fun<<std::endl;
>      return 0;
> }
>
> it would be of great help if you can guide me
>
>
>
> --
> View this message in context: http://boost.2283326.n4.nabble.com/returning-a-ublas-matrix-from-a-function-tp4666050p4666070.html
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