On 07/05/18 12:39 -0400, Ed Smith-Rowland wrote:
All,
We were using a different convention for P_l^m assoc_legendre(int l,
int m, FloatTp x)
- the so-called Condon-Shortley convention which includes (-1)^m.
This unfortunately is common.
This factor is taken out to match the standard. The underlying
__detail code has an arg that allows you to flip this
- mostly to highlight the subtle difference.
The related sph_legendre is unaffected by this (our impl and the
standard include the C-S phase).
OK for trunk and branches?
Ed
2018-05-07 Edward Smith-Rowland <3dw...@verizon.net>
PR libstdc++/83140 - assoc_legendre returns negated value when m is odd
* include/tr1/legendre_function.tcc (__assoc_legendre_p): Add __phase
argument defaulted to +1. Doxy comments on same.
* testsuite/special_functions/02_assoc_legendre/
check_assoc_legendre.cc: Regen.
* testsuite/tr1/5_numerical_facilities/special_functions/
02_assoc_legendre/check_tr1_assoc_legendre.cc: Regen.
Index: include/tr1/legendre_function.tcc
===================================================================
--- include/tr1/legendre_function.tcc (revision 259973)
+++ include/tr1/legendre_function.tcc (working copy)
@@ -65,7 +65,7 @@
namespace __detail
{
/**
- * @brief Return the Legendre polynomial by recursion on order
+ * @brief Return the Legendre polynomial by recursion on degree
* @f$ l @f$.
*
* The Legendre function of @f$ l @f$ and @f$ x @f$,
@@ -74,7 +74,7 @@
* P_l(x) = \frac{1}{2^l l!}\frac{d^l}{dx^l}(x^2 - 1)^{l}
* @f]
*
- * @param l The order of the Legendre polynomial. @f$l >= 0@f$.
+ * @param l The degree of the Legendre polynomial. @f$l >= 0@f$.
* @param x The argument of the Legendre polynomial. @f$|x| <= 1@f$.
*/
template<typename _Tp>
@@ -127,16 +127,19 @@
* P_l^m(x) = (1 - x^2)^{m/2}\frac{d^m}{dx^m}P_l(x)
* @f]
*
- * @param l The order of the associated Legendre function.
+ * @param l The degree of the associated Legendre function.
* @f$ l >= 0 @f$.
* @param m The order of the associated Legendre function.
* @f$ m <= l @f$.
* @param x The argument of the associated Legendre function.
* @f$ |x| <= 1 @f$.
+ * @param phase The phase of the associated Legendre function.
+ * Use -1 for the Condon-Shortley phase convention.
*/
template<typename _Tp>
_Tp
- __assoc_legendre_p(unsigned int __l, unsigned int __m, _Tp __x)
+ __assoc_legendre_p(unsigned int __l, unsigned int __m, _Tp __x,
+ _Tp __phase = _Tp{+1})
This list-init isn't valid for C++98 i.e. when used via <tr1/cmath>.
GCC seems to allow it, but Clang won't.
We could consider dropping the TR1 support, and just provide these
functions for ISO/IEC 29124:2010 in C++11 (or later) and for C++17.
But that decision should be taken separately, and should only happen
on trunk anyway so we need to use _Tp(+1) here.
OK for trunk with _Tp(+1) instead of _Tp{+1}.
Do we want to change the result of these functions on the branches?
How likely is it that changing it will affect somebody's calcuations
in a way that they don't expect from a minor release on a branch?
