Dear ublas developers!
(I am using boost 1.30 & gcc 3.2)
the following program:
#include
#include
int main () {
using namespace boost::numeric::ublas;
matrix<double> m (4, 4);
for (unsigned int i = 0; i < m.size1 (); ++ i)
for (unsigned int j = 0; j < m.size2 (); ++ j)
m(i, j) = 1;
std::cout << m << std::endl;
// multiply a slice of the matrix with 2....
project (m, slice (2, 1, m.size1()-2), slice (1, 0, m.size1()-2)) *= 2;
// interesting result ... the slice has been multiplied with 4
std::cout << m << std::endl;
}
gives the following output:
[4,4]((1,1,1,1),(1,1,1,1),(1,1,1,1),(1,1,1,1))
[4,4]((1,1,1,1),(1,1,1,1),(1,4,1,1),(1,4,1,1))
Why is the slice multiplied with 4 and not with 2?? Do I make some
fundamental mistake? Everything works fine if I am using a
matrix_vector_slice.
My second (stupid?) question is the following: Is it intentional, that it
is not possible to compile:
#include
#include
int main () {
using namespace boost::numeric::ublas;
matrix<double> m (4, 4);
for (unsigned int i = 0; i < m.size1 (); ++ i)
for (unsigned int j = 0; j < m.size2 (); ++ j)
m(i, j) = 4*i+j;
std::cout << m << std::endl;
swap(row(m,0), row(m,2));
std::cout << m << std::endl;
}
whereas
matrix_row l(m, 0);
matrix_row r(m, 2);
swap(l, r); /* swap the rows */
works fine. MTL has support for a similar syntax:
swap(rows(m)[0], rows(m)[2]);
best regards and thanks for your help!
Stephan
