a) The description in the HTML manual on the Chebyshev Approximations
in http://www.gnu.org/software/gsl/manual/gsl-ref_28.html#SEC413
is slightly out of date, because in the typedef struct {...} gsl_cheb_struct
the last component of the structure, int order_sp, is missing. Also,
it seems that this is know called gsl_series_struct, not gsl_cheb_struct (?).

b) Since the standard application of the Debye function with black body
radiation "starts" a power of n=3, and the current implementation in
specfunc/debye.c and specfunc/gsl_sf_debye.h reaches only to n=4, this
is somewhat too short if one wants to compile moments over black body functions.
Therefore I propose to extend the implementation to n=5 and n=6,
as in the implementation attached.
===============================================================================
Richard J Mathar                Tel (+31) (0) 71 527 8459
Sterrewacht Universiteit Leiden Fax (+31) (0) 71 527 5819
Postbus 9513
2300 RA Leiden               
The Netherlands                 URL http://www.strw.leidenuniv.nl/~mathar