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[libstdc++, PATCH] PR libstdc++/83140 - assoc_legendre returns negated value when m is odd.

From: Ed Smith-Rowland <3dw4rd at verizon dot net>
To: "libstdc++ at gcc dot gnu dot org" <libstdc++ at gcc dot gnu dot org>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Jonathan Wakely <jwakely dot gcc at gmail dot com>
Date: Mon, 7 May 2018 12:39:14 -0400
Subject: [libstdc++, PATCH] PR libstdc++/83140 - assoc_legendre returns negated value when m is odd.

All,

We were using a different convention for P_l^m assoc_legendre(int l, intm, 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 __detailcode 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 thestandard include the C-S phase).


OK for trunk and branches?

Ed

Attachment: CL_pr83140
Description: Text document

Attachment: patch_pr83140
Description: Text document

Follow-Ups:
- Re: [libstdc++, PATCH] PR libstdc++/83140 - assoc_legendre returns negated value when m is odd.
  - From: Jonathan Wakely

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