Er:Re: [Bug-gsl] discontinuity in dilog function

[Jim McElwaine]

Hi Gerard

I managed to compile the function with the rest of gsl 1.5

It is now appears to be fine for |q|<pi. 
I've tested it for continuity and satisfying  d/dz = log(1-z)/z

It still discontinuous for |q|>pi. I imagine this is easy to fix.


Very impressed by the speed of your response.

Thanks.

Jim



Gerard Jungman writes:
 > 
 > 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
 > 
 > 
 > 

-- 
Dr. Jim McElwaine   
H0.15, Department of Applied Maths and Theoretical Physics
Centre for Mathematical Sciences, Cambridge University  
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