URL:
<http://savannah.gnu.org/bugs/?29606>
Summary: insufficient argument checks in gsl_sf_coupling_6j
Project: GNU Scientific Library
Submitted by: bjg
Submitted on: Mon Apr 19 11:53:28 2010
Category: Runtime error
Severity: 3 - Normal
Operating System:
Status: None
Assigned to: None
Open/Closed: Open
Release: 1.14
Discussion Lock: Any
_______________________________________________________
Details:
From: "Hergert, Heiko" <[email protected]>
To: <[email protected]>
Subject: [Bug-gsl] Error in 6j symbol routine (gsl_sf_coupling_6j)
Date: Thu, 15 Apr 2010 15:11:24 -0400
Hi,
I just came about this bug in gsl_sf_coupling_6j() in GSL 1.13 (haven't
checked newer builds).
The check of the triangle conditions (via the routine
triangle_selection_fails) doesn't properly rule out all unphysical
combinations of angular momenta. For instance
gsl_sf_coupling(0, 2, 2, 44, 43, 43) = 0.087039
but the routine should return 0 since this symbol is unphysical:
jb=1 and jc=21 cannot be coupled to jf=43/2=21.5 although the triangle
tests are nominally satisfied
abs(1-21.5)=20.5 <= 21 <= 22.5.
A possible fix would be to check if
(two_ja + two_jb + two_jc)%2 == 0
ja+jb+jc is always integer in physically allowed couplings (i.e.,
2*(ja+jb+jc) must be even).
The routine for the 3j symbol is not similarly affected due to the
additional m_selection_fails() test.
--
<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
<< Heiko Hergert
<< National Superconducting Cyclotron Laboratory
<< Michigan State University
<<
<< phone: +1 517 908 7472
<< mail: [email protected]
<< www : http://www.nscl.msu.edu
<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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