Re: [Bug-gsl] discontinuity in dilog function

[Gerard Jungman]

Hi. Thanks.

There used to be some argument reduction code in dilog.c, but
it got commented out at some point. I don't know if I did it
or somebody else did. Brian? That function was a bit of a mess.
It may be fixed now. Fixes now in CVS. More testing is
almost certainly needed.

-- 
Gerard Jungman <address@hidden>
Los Alamos National Laboratory


On Fri, 2004-09-10 at 11:44, Jim McElwaine wrote:
> The complex dilog function has a discontinuity at |x| = 1 
> int the lower half plane if arg(x)<0 or arg(x)>pi
> 
> gsl_sf_complex_dilog_e (r, q, Re(z), Im(z))
> r = abs(x)
> q = arg(x)
> 
> q=-pi/2 r = .9  z = -0.1718 - 0.8360i
> q=-pi/2 r = 1   z = -0.2056 - 0.9160i
> q=-pi/2 r = 1.1 z =  9.6286 - 0.9931i   XXXXXXX incorrect
> 
> Note that in the upper half plane there is no problem
> q=pi/2 r = .9  z = -0.1718 + 0.8360i
> q=pi/2 r = 1   z = -0.2056 + 0.9160i
> q=pi/2 r = 1.1 z = -0.2410 + 0.9931i 
> 
> Jim