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Fix initialization of power series so that we don't get a spurious overflow error from tgamma when the result is actually zero.

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[SVN r86415]
This commit is contained in:
John Maddock
2013-10-24 08:35:41 +00:00
parent 8725243986
commit fb52d2de42
1 changed files with 13 additions and 1 deletions
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14
include/boost/math/special_functions/bessel.hpp
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@@ -48,7 +48,13 @@ struct sph_bessel_j_small_z_series_term
{
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);
}
else
term = pow(mult, T(v)) / boost::math::tgamma(v+1+T(0.5f), Policy());
mult *= -mult;
}
T operator()()
@@ -142,6 +148,11 @@ inline T sph_bessel_j_imp(unsigned n, T x, const Policy& pol)
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 +763,4 @@ inline OutputIterator cyl_neumann_zero(T v,
#endif // BOOST_MATH_BESSEL_HPP