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

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