possible bug in gsl_sf_hyperg_U

[Stefan Gerlach <stefan dot gerlach at uni-konstanz dot de>]

Hi,

I have a problem using gsl_sf_hyperg_U with certain arguments.
running this example

       for(z=3.0;z>0.0;z-=0.1)
                printf("%g %g\n",z,gsl_sf_hyperg_U(-2.0,4.0,z));

i get 

	...
	2.2 2.84
	2.1 3.41
	2 4
	gsl: psi.c:381: ERROR: domain error
	Default GSL error handler invoked.
	Aborted

AFAIK the hypergeometricU is well defined for z> 0.0.
I get the same error with gsl-1.11. Any ideas?

-- 
Stefan Gerlach

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