matrix<math::real, 3> linear(const rigid::skeleton& skel, const config& at) {
const natural n = skel.size();
assert( at.rows() == n );
mat res = mat::Zero(3, 6*n);
skel.each( [&](math::natural i) {
res.block<3, 3>(0, 6*i + 3) = skel.topology[i].mass * at(i).rotation().matrix();
});
return std::move(res);
}
matrix<math::real, 3> angular(const rigid::skeleton& skel, const config& at) {
const natural n = skel.size();
assert( at.rows() == n );
mat res = mat::Zero(3, 6*n);
const vec3 c = com(skel) ( at );
skel.each( [&](math::natural i) {
res.block<3, 3>(0, 6*i) = at(i).rotation().matrix() * skel.topology[i].inertia.asDiagonal();
const vec3 ri = at(i).translation() - c;
res.block<3, 3>(0, 6*i + 3) = skel.topology[i].mass * math::hat( ri )
* at(i).rotation().matrix();
});
return std::move(res);
}