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

**From**: |
Gerard Jungman |

**Subject**: |
Re: [Bug-gsl] discontinuity in dilog function |

**Date**: |
Mon, 13 Sep 2004 14:01:55 -0600 |

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*