This should not compile. I'll look into it. You probably need to fragment it into SI base units.

yes I was thinking something like that, like creating an si::energy_base_unit but then it will be full of base units if I do it this for every dimension. Besides it worked in one direction.

If you could provide either the error message, or even better, the definition of the atomic system, I could help more.

this is gcc 4.4.1, boost-1.40 error messages, atomic.hpp and main.cpp are attached below. Thank you, Alfredo ---begin error message ----------------------------------- In file included from /usr/include/boost/units/conversion.hpp:14, from /usr/include/boost/units/quantity.hpp:29, from eos.cpp:7: /usr/include/boost/units/detail/conversion_impl.hpp: In instantiation of ‘boost::units::detail::conversion_impl<1>::apply >, boost::units::dimensionless_type>, boost::units::homogeneous_system > >, boost::units::list > > > >’: /usr/include/boost/units/detail/conversion_impl.hpp:445: instantiated from ‘boost::units::detail::conversion_factor_helper >, boost::units::dimensionless_type>, boost::units::heterogeneous_system >, boost::units::dimensionless_type>, boost::units::list >, boost::units::dimensionless_type>, boost::units::dimensionless_type>

, void>, boost::units::unit >, boost::units::dimensionless_type>, boost::units::heterogeneous_system >, boost::units::list > >, boost::units::static_rational<1l, 2l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::list >, boost::units::dimensionless_type>, boost::units::dimensionless_type> , void> >’ /usr/include/boost/units/detail/conversion_impl.hpp:274: instantiated from ‘boost::units::detail::call_base_unit_converter_impl<false>::apply >, boost::units::dimensionless_type>, boost::units::heterogeneous_system >, boost::units::list > >, boost::units::static_rational<1l, 2l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::list >, boost::units::dimensionless_type>, boost::units::dimensionless_type> , void> >’ /usr/include/boost/units/detail/conversion_impl.hpp:289: instantiated from ‘boost::units::detail::call_base_unit_converter >, boost::units::dimensionless_type>, boost::units::heterogeneous_system >, boost::units::list > >, boost::units::static_rational<1l, 2l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::list >, boost::units::dimensionless_type>, boost::units::dimensionless_type> , void> >’ /usr/include/boost/units/detail/conversion_impl.hpp:316: instantiated from ‘boost::units::detail::conversion_impl<1>::apply >, boost::units::dimensionless_type>, boost::units::homogeneous_system > >, boost::units::list > > > >’ /usr/include/boost/units/detail/conversion_impl.hpp:316: instantiated from ‘boost::units::detail::conversion_impl<2>::apply > >, boost::units::static_rational<1l, 1l> >, boost::units::list >, boost::units::dimensionless_type> >, boost::units::homogeneous_system > >, boost::units::list > > > >’ /usr/include/boost/units/detail/conversion_impl.hpp:316: instantiated from ‘boost::units::detail::conversion_impl<3>::apply >, boost::units::list > >, boost::units::static_rational<1l, 1l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > >, boost::units::list > > > >’ /usr/include/boost/units/detail/conversion_impl.hpp:445: instantiated from ‘boost::units::detail::conversion_factor_helper >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::heterogeneous_system >, boost::units::list > >, boost::units::static_rational<1l, 1l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::list >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::dimensionless_type> >, void>, boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::heterogeneous_system >, boost::units::dimensionless_type>, boost::units::list >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::dimensionless_type> >, void> >’ /usr/include/boost/units/detail/conversion_impl.hpp:40: instantiated from ‘boost::units::detail::conversion_factor_helper >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > >, boost::units::list > > > > > > > > >, void>, boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > > > > >, void> >’ /usr/include/boost/units/detail/conversion_impl.hpp:345: instantiated from ‘static boost::units::quantity boost::units::conversion_helper, boost::units::quantity >::convert(const boost::units::quantity&) [with Unit1 = boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > >, boost::units::list > > > > > > > > >, void>, T1 = double, Unit2 = boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > > > > >, void>, T2 = double]’ /usr/include/boost/units/quantity.hpp:193: instantiated from ‘boost::units::quantity::quantity(const boost::units::quantity&, typename boost::disable_if::type, boost::units::detail::is_non_narrowing_conversion, mpl_::bool_<true>, mpl_::bool_<true>, mpl_::bool_<true> >, typename boost::units::detail::disable_if_is_same::type>::type*) [with Unit2 = boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > >, boost::units::list > > > > > > > > >, void>, YY = double, Unit = boost::units::unit >, boost::units::list >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system > > > > >, void>, Y = double]’ eos.cpp:89: instantiated from here /usr/include/boost/units/detail/conversion_impl.hpp:316: error: no type named ‘type’ in ‘struct boost::units::detail::call_base_unit_converter >, boost::units::dimensionless_type>, boost::units::heterogeneous_system >, boost::units::list > >, boost::units::static_rational<1l, 2l> >, boost::units::list >, boost::units::dimensionless_type> > >, boost::units::list >, boost::units::dimensionless_type>, boost::units::dimensionless_type> , void> >’ compilation terminated due to -Wfatal-errors. ---end error message --------------------------------

---begin atomic.hpp--------------------------------------------------------------------------------------------------------------------------------- #include //equivalent to includes in units/systems/si/base.hpp #include #include #include //#include //do not remove: '...has initializer but incomplete type...' error //equivalent to includes in //equivalent to ./base_units/si/*.hpp #include #include #include #include #include #include #include #include #include //equivalent to ./base_units/si/*.hpp namespace boost{ namespace units{ namespace atomic{ //define namespace au=boost::units::atomic if necessary using std::string; // taken from http://en.wikipedia.org/wiki/Atomic_units#Fundamental_units struct electron_mass_base_unit : base_unit{ static string name() {return ("electron_mass");} static string symbol() {return ("me");} }; //equivalent to ./base_units/si/meter.hpp> struct bohr_radius_base_unit : base_unit{ static string name() {return ("bohr_radius");} static string symbol() {return ("a0");} }; struct elementary_charge_base_unit : base_unit{ static string name() {return ("elementary_charge");} static string symbol() {return ("e");} }; struct reduced_planck_constant_base_unit : base_unit{ static string name() {return ("reduced_planck_constant");} static string symbol() {return ("hbar");} }; struct hartree_energy_base_unit : base_unit{ static string name() {return ("hartree_energy");} static string symbol() {return ("Eh");} }; }}}//nss //similar to ./systems/si/base.hpp namespace boost{ namespace units{ namespace atomic{ typedef make_system< electron_mass_base_unit, bohr_radius_base_unit, elementary_charge_base_unit, reduced_planck_constant_base_unit, hartree_energy_base_unit >::type system; }}} //equivalent to units/systems/si/.*.hpp namespace boost{ namespace units{ namespace atomic{ typedef unit dimensionless; typedef unit mass; typedef unit length; typedef unit electric_charge; typedef unit angular_momentum; typedef unit energy; static const mass electron_mass; static const length bohr_radius, bohr; static const electric_charge elementary_charge; static const angular_momentum reduced_planck_constant; static const energy hartree_energy, hartree; }}} #include //derived, equiv for example to units/systems/si/area.hpp namespace boost{ namespace units{ namespace atomic{ typedef unit area; typedef unit volume; typedef unit pressure; }}} ---end atomic.hpp ---begin main.cpp------------------------------------------------------------------------------------------------------------------------------------- #include #include #include #include //helps transforms the output from kg/m/s^2 to J #include #include #include #include #include"boost/units/atomic.hpp" //#include #include<iostream> #include"boost/units/base_units/metric/angstrom.hpp" namespace boost{ namespace units{ namespace metric{ typedef metric::angstrom_base_unit::unit_type angstrom_unit; BOOST_UNITS_STATIC_CONSTANT(angstrom, angstrom_unit); }}} /* namespace boost { namespace units { typedef metric::angstrom_base_unit::unit_type angstrom_unit; BOOST_UNITS_STATIC_CONSTANT(angstrom, angstrom_unit); typedef scaled_base_unit< si::meter_base_unit, scale<10, static_rational<-9> > > nanometer_base_unit; typedef nanometer_base_unit::unit_type nanometer_unit; BOOST_UNITS_STATIC_CONSTANT(nanometer, nanometer_unit); // typedef make_scaled_unit > >::type nanometer; } } // namespace boost::units */ using std::clog; using std::endl; using namespace boost::units; class vinet{ public: class parameters{ public: quantityatomic::volume v0; //volume quantityatomic::energy phi0; }; }; BOOST_UNITS_DEFINE_CONVERSION_FACTOR( atomic::bohr_radius_base_unit, metric::angstrom_base_unit, double, 0.529177209 ); #include BOOST_UNITS_DEFINE_CONVERSION_FACTOR( atomic::hartree_energy_base_unit, si::energy, double, 4.359744e-18 ); //compiles but doesn't help for en3 BOOST_UNITS_DEFINE_CONVERSION_FACTOR( si::energy, atomic::hartree_energy_base_unit, double, 1./4.359744e-18 ); int main(){ quantitysi::length l1(1.*si::meter); //works quantitysi::length l2(1.*atomic::bohr); //works quantityatomic::length l3(1.*atomic::bohr); //works quantityatomic::length l4(1.*si::meter); //works quantitysi::energy en1(1.*si::joules); //works quantitysi::energy en2(1.*atomic::hartree); //works quantityatomic::energy en3(1.*atomic::hartree); //work quantityatomic::energy en4(1.*si::joules); //does not work, compilation error return 0; } ---end main.cpp

What you're missing is the conversion from s to m kg^-1 Eh^-1/2.  (I think the conversion factor should be sqrt(4.359744e-18))

you probably mean s to m kg^1/2 Eh^-1/2 and yes that is the conversion factor. Now, I have no idea what would be the syntax to transform from second to something with combined units BOOST_UNITS_DEFINE_CONVERSION_FACTOR( si::second, ???, double, sqrt(4.359744e-18) );

You could also make it work by adding BOOST_UNITS_DEFAULT_CONVERSION(     atomic::hartree_energy_base_unit,     si::energy );

that worked right away. What would be the drawback of using DEFAULT_CONVERSION macro? loss of precision perhaps? Thank you, Alfredo

AMDG alfC wrote:

...

that worked right away. What would be the drawback of using DEFAULT_CONVERSION macro? loss of precision perhaps?

actually, the question is more profound, from the design of the library it seems that you were very careful not to make any transformation automatically because loss of precision.

The idea is that you can specify as many direct conversions as you want, and the library will use the default one only if it can't find the one it really wants. In fact, we use DEFAULT_CONVERSION for most of the non-SI units.

If that is the case I would like to follow your design principle. On the other hand, even if I want to work in atomic units (motivated by the order of magnitudes of the quantities) it is inevitable to output some of the results in SI. The question is does it make sense to have this transformation from Hartree to Joule with such an huge exponent.

It's probably okay. double can handle values up to about 10^300

Following your design, would it be better to have a conversion from Hartree to some scaled unit of Joule (femtoJoule) instead, so all the machine number have small exponents?

I'm not a floating point expert, but if you're just doing the conversion for output, it probably doesn't matter. In Christ, Steven Watanabe