projection of full parameter vector on sub-space (was ACTS-28)

Original author Christian Gumpert @cgumpert

Can the projection of a full parameter vector onto a parameter sub-space be optimized? Instead of multiplying the full parameter vector with the (very sparse) projection matrix, one could try to "pick" the right entries from the full vector.

template<typename Policy,ID_t... values>
class ParameterSet
{
  ...
  ParVector_t project(const FullParameterSet<policy>& fullParSet) const;
};