Re: [Boost-users] Problem with user defined Boost Units system

Matthias, I appreciate your response. Yes I did not compile my example. I should have done that. I took your example and then trimmed down the header file so I can reproduce the error. I am not sure what is wrong here. I get an error not because the destination type is incorrect. It does not even reach that point. I get an error that there is no division operator: [storri@fedora Source]$ g++ -o boost_units boost_units.cpp boost_units.cpp: In function ‘int main(int, char**)’: boost_units.cpp:44:39: error: no match for ‘operator/’ in ‘1 / boost::units::operator-(const boost::units::quantity&, const boost::units::quantity&) [with Unit1 = boost::units::unit >, boost::units::dimensionless_type>, boost::units::homogeneous_system > > > >, Unit2 = boost::units::unit >, boost::units::dimensionless_type>, boost::units::homogeneous_system > > > >, X = double, Y = double, typename boost::units::subtract_typeof_helper, boost::units::quantity >::type = boost::units::quantity >, boost::units::dimensionless_type>, boost::units::homogeneous_system > > > >, double>]((*(const boost::units::quantity >, boost::units::dimensionless_type>, boost::units::homogeneous_system > > > >, double>*)(& val2)))’ If I remove the "radii_t result =" from the following code and comment out the IO statement I get the same error as previously quoted above. Below is the code I used. I appreciate your patience as I learn Boost Units. Q1: What is the reason for this error? What in the error output helped you to figure that out. Q2: Even if the above error did not exist you mentioned that it would fail the dimensional analysis. I think we both agree the type would be radii^-1. How do you declare a type to be raised to the correct power? Stephen ------------------------- #include #include #include #include #include #include #include #include <iostream> namespace myproject { namespace types { struct radii_base_unit : public boost::units::base_unit { static std::string name() { return("radii"); } static std::string symbol() { return("r"); } }; struct minute_base_unit : public boost::units::base_unit { static std::string name() { return ("minute"); } static std::string symbol() { return ("min"); } }; typedef boost::units::make_system::type myproject_system_t; typedef boost::units::unitboost::units::length_dimension,myproject_system_t myproject_length; typedef boost::units::quantity radii_t; BOOST_UNITS_STATIC_CONSTANT(radii,myproject_length); } } int main ( int, char** ) { using namespace myproject::types; radii_t val1 ( 5 * radii ); radii_t val2 ( 3 * radii ); radii_t result = 1.0 / ( val1 - val2 ); std::cout << result << std::endl; return 0; } On 12/1/11, Matthias Schabel wrote:

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I am trying to understand the dimensionality of the following two equations.

--- first equation --- example::types::radii_t val1 = 5 * example::types::radii; example::types::radii_t val2 = 4 * example::types::radii;

example::types::radii_t L1 = 1 / ( val1 - va2 );

va2->val2

This should give you a compile error anyway, since you are trying to assign a length to an inverse length...

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If I was doing the dimensional analysis by hand I would see

1 / ( radii - radii )

Such that the end type would be

radii^-1

Given that end type here is the second equation:

example::types::radii_t val3 = 5 * example::types::radii; example::types::dimensionless_t val4 = 10; example::types::dimensionless_t L2 = L1 * val4 * val3;

Doing the dimensional analysis by hand I think I should see:

L2 = radii * (nothing) * radii^-1 = (nothing) or dimensionless

What Boost Units is reporting is that L2 is actually units in radii_t.

I'm not sure I believe you; the code you pasted is not compilable...did you actually compile anything?

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--------- QUESTIONS --------------

Q1: How do you print out the types at compile time?

Q2: How can you confirm you have the correc power for a type? For example radii is indeed raised to the -1 power.

Using your earlier header :

#include "types.hpp"

#include <iostream> #include

using namespace myproject::types;

int main() { radii_t val1(5*radii), val2(4*radii);

//auto L1 = 1/(val1-val2); // compile time error due to failed dimensional consistency

radii_t val3(5*radii);

dimensionless_t val4 = 10; dimensionless_t L2(val3*val4/(val1-val2));

std::cout << val1 << std::endl << val2 << std::endl << val3 << std::endl << val4 << std::endl << L2 << std::endl;

return 0; }

gives

5 r 4 r 5 r 10 dimensionless 50 dimensionless