/usr/include/boost/math/special_functions
Edit: /usr/include/boost/math/special_functions/binomial.hpp (2508B)
// Copyright John Maddock 2006.
// Use, modification and distribution are subject to the
// Boost Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_MATH_SF_BINOMIAL_HPP
#define BOOST_MATH_SF_BINOMIAL_HPP
#ifdef _MSC_VER
#pragma once
#endif
#include
#include
#include
#include
namespace boost{ namespace math{
template
T binomial_coefficient(unsigned n, unsigned k, const Policy& pol)
{
BOOST_STATIC_ASSERT(!boost::is_integral::value);
BOOST_MATH_STD_USING
static const char* function = "boost::math::binomial_coefficient<%1%>(unsigned, unsigned)";
if(k > n)
return policies::raise_domain_error(
function,
"The binomial coefficient is undefined for k > n, but got k = %1%.",
static_cast(k), pol);
T result;
if((k == 0) || (k == n))
return static_cast(1);
if((k == 1) || (k == n-1))
return static_cast(n);
if(n <= max_factorial::value)
{
// Use fast table lookup:
result = unchecked_factorial(n);
result /= unchecked_factorial(n-k);
result /= unchecked_factorial(k);
}
else
{
// Use the beta function:
if(k < n - k)
result = k * beta(static_cast(k), static_cast(n-k+1), pol);
else
result = (n - k) * beta(static_cast(k+1), static_cast(n-k), pol);
if(result == 0)
return policies::raise_overflow_error(function, 0, pol);
result = 1 / result;
}
// convert to nearest integer:
return ceil(result - 0.5f);
}
//
// Type float can only store the first 35 factorials, in order to
// increase the chance that we can use a table driven implementation
// we'll promote to double:
//
template <>
inline float binomial_coefficient >(unsigned n, unsigned k, const policies::policy<>& pol)
{
return policies::checked_narrowing_cast >(binomial_coefficient(n, k, pol), "boost::math::binomial_coefficient<%1%>(unsigned,unsigned)");
}
template
inline T binomial_coefficient(unsigned n, unsigned k)
{
return binomial_coefficient(n, k, policies::policy<>());
}
} // namespace math
} // namespace boost
#endif // BOOST_MATH_SF_BINOMIAL_HPP