Subject: [Boost-commit] svn:boost r86343 - in trunk: boost/math/special_functions libs/math/test
From: john_at_[hidden]
Date: 2013-10-17 14:21:56
Author: johnmaddock
Date: 2013-10-17 14:21:56 EDT (Thu, 17 Oct 2013)
New Revision: 86343
URL: http://svn.boost.org/trac/boost/changeset/86343
Log:
Fix for sph_bessel when v is large and x is small.
Text files modified:
trunk/boost/math/special_functions/bessel.hpp | 17 ++++++++++++++++-
trunk/libs/math/test/test_bessel_j.hpp | 7 +++++++
2 files changed, 23 insertions(+), 1 deletions(-)
Modified: trunk/boost/math/special_functions/bessel.hpp
==============================================================================
--- trunk/boost/math/special_functions/bessel.hpp Thu Oct 17 13:34:31 2013 (r86342)
+++ trunk/boost/math/special_functions/bessel.hpp 2013-10-17 14:21:56 EDT (Thu, 17 Oct 2013) (r86343)
@@ -48,7 +48,16 @@
{
BOOST_MATH_STD_USING
mult = x / 2;
- term = pow(mult, T(v)) / boost::math::tgamma(v+1+T(0.5f), Policy());
+ if(v + 3 > max_factorial<T>::value)
+ {
+ // term = v * log(mult) - boost::math::lgamma(v+1+T(0.5f), Policy());
+ // term = exp(term);
+ // Denominator increases faster than numerator each time v increases by one,
+ // so if tgamma would overflow then the result is necessarily zero.
+ term = 0;
+ }
+ else
+ term = pow(mult, T(v)) / boost::math::tgamma(v+1+T(0.5f), Policy());
mult *= -mult;
}
T operator()()
@@ -142,6 +151,11 @@
if(n == 0)
return boost::math::sinc_pi(x, pol);
//
+ // Special case for x == 0:
+ //
+ if(x == 0)
+ return 0;
+ //
// When x is small we may end up with 0/0, use series evaluation
// instead, especially as it converges rapidly:
//
@@ -752,3 +766,4 @@
#endif // BOOST_MATH_BESSEL_HPP
+
Modified: trunk/libs/math/test/test_bessel_j.hpp
==============================================================================
--- trunk/libs/math/test/test_bessel_j.hpp Thu Oct 17 13:34:31 2013 (r86342)
+++ trunk/libs/math/test/test_bessel_j.hpp 2013-10-17 14:21:56 EDT (Thu, 17 Oct 2013) (r86343)
@@ -262,6 +262,13 @@
do_test_sph_bessel_j<T>(sph_bessel_data, name, "Bessel j: Random Data");
//
+ // Some special cases:
+ //
+ BOOST_CHECK_EQUAL(boost::math::sph_bessel(0, T(0)), T(1));
+ BOOST_CHECK_EQUAL(boost::math::sph_bessel(1, T(0)), T(0));
+ BOOST_CHECK_EQUAL(boost::math::sph_bessel(100000, T(0)), T(0));
+
+ //
// Special cases that are errors:
//
BOOST_CHECK_THROW(boost::math::cyl_bessel_j(T(-2.5), T(0)), std::domain_error);