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#### tommath_rational

`#include <boost/multiprecision/tommath.hpp>`

    namespace boost{ namespace multiprecision{

    typedef rational_adpater<tommath_int>        tommath_rational;
    typedef number<tommath_rational >         tom_rational;

    }} // namespaces

The `tommath_rational` back-end is used via the typedef `boost::multiprecision::tom_rational`. It acts as a thin wrapper around `boost::rational<tom_int>` to provide a rational number type that is a drop-in replacement for the native C++ number types, but with unlimited precision.

The advantage of using this type rather than `boost::rational<tom_int>` directly, is that it is expression-template enabled, greatly reducing the number of temporaries created in complex expressions.

There are also non-member functions:

    tom_int numerator(const tom_rational&);
    tom_int denominator(const tom_rational&);

which return the numerator and denominator of the number.

Things you should know when using this type:

- Default constructed `tom_rational`s have the value zero (this the inherited Boost.Rational behavior).
- Division by zero results in a `std::overflow_error` being thrown.
- Conversion from a string results in a `std::runtime_error` being thrown if the string can not be interpreted as a valid rational number.
- No changes are made to libtommath's global state, so this type can safely coexist with other libtommath code.
- Performance of this type has been found to be pretty poor - this need further investigation - but it appears that Boost.Rational needs some improvement in this area.

###### Example:

    #include <boost/multiprecision/tommath.hpp>
    #include <iostream>

    int main()
    {
       using namespace boost::multiprecision;

       tom_rational v = 1;

       // Do some arithmetic:
       for(unsigned i = 1; i <= 1000; ++i)
          v *= i;
       v /= 10;

       std::cout << v << std::endl; // prints 1000! / 10
       std::cout << numerator(v) << std::endl;
       std::cout << denominator(v) << std::endl;

       tom_rational w(2, 3); // Component wise constructor
       std::cout << w << std::endl; // prints 2/3

       return 0;
    }