Re: [Boost-Users] ublas::matrix sharing storage with ublas::vector

28 Nov 2002

      Great! This is exactly what I was looking for. Is there a list of all these
undocumenated features in boost anywhere besides the source?

Here is a snippet of code that does exactly what I want.

#define BOOST_UBLAS_SIMPLE_ARRAY_ADAPTOR
#include 
#include 
#include 

using namespace boost::numeric::ublas;

main()
{
   matrix<double> m(5,5);
   vector v(m.data().size(),array_adaptor<double>(m.data().size(),m.data().begin()));

   for (int i = 0; i < 25; i++)
     v[i] = i;

   std::cout << v << std::endl;
   std::cout << m << std::endl;
}

--Stephen

On Thu, Nov 28, 2002 at 11:43:11AM +0100, Kresimir Fresl wrote:
...
Stephen Crowley wrote:
...
For example.. I have a matrix<double> m(5,5);
In some code I actually need to use it as a 5x5 matrix.. but other parts
must reference it as a vector (to pass to another library).
Currently I am doing something like this
matrix<double> m(5,5);
// do stuff to m
vector<double> v(25);
v.data() = m.data();
// pass v to library
// get results back
m.data() = v.data();
This is obviously not optimal.. and if both m.data() and v.data() pointed to
the same location in memory the problem would be solved.
I suppose I might be able to get around it by making my own storage class
that allows you to specify a location and size instead of allocating one
itself.
There is a storage class `array_adaptor<>' (in storage.hpp, currently
undocumented), which adapts some other array to interface
which ublas classes expect:
==============================================
#include <cstddef>
#include <iostream>
#define BOOST_UBLAS_SIMPLE_ARRAY_ADAPTOR
#include 
#include 
#include 
typedef boost::numeric::ublas::array_adaptor<double> storage_t;
typedef boost::numeric::ublas::vector vct_t;
typedef boost::numeric::ublas::row_major rm_t;
typedef boost::numeric::ublas::matrix matr_t;
int main() {
std::size_t n = 5;
   std::size_t nxn = n * n;
double *a = new double[nxn];
   storage_t st (nxn, a);
vct_t v (nxn, st);
   for (std::size_t i = 0; i < nxn; ++i)
     v (i) = i + 0.1;
   std::cout << v << std::endl;
matr_t m (n, n, st);
   std::cout << m << std::endl;
for (std::size_t i = 0; i < n; ++i)
     for (std::size_t j = 0; j < n; ++j)
       m (i, j) = 10 * i + j + 0.1;
std::cout << v << std::endl;
   std::cout << m << std::endl;
delete[] a;
}
==============================================
[Note that BOOST_UBLAS_SIMPLE_ARRAY_ADAPTOR must
be defined. Otherwise array_adaptor<> uses boost::shared_array<>
which doesn't have operator+, which is in turn needed in some
functions -- Joerg, are you listening?]
Hope this helps,
fres
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-- 
Stephen