gamma

Synopsis

Calculate the Gamma function

gamma(z)

Description

Calculate the CEPHES function, Gamma, in the range [-171 < z <= 171.6]. The command returns the Gamma function of the argument (scalar or array).

Arguments |x| <= 34 are reduced by recurrence and the function approximated by a rational function of degree 6/7 in the interval (2,3). Large arguments are handled by Stirling's formula. Large negative arguments are made positive using a reflection formula.

Relative error:

Error for arguments outside the test range will be larger owing to error amplification by the exponential function.

Reference

Cephes Math Library Release 2.0: April, 1987. Copyright 1985, 1987 by Stephen L. Moshier. Direct inquiries to 30 Frost Street, Cambridge, MA 02140.

Example 1

sherpa> gamma(3.14)

Calculate the gamma of z=3.14 .

Example 2

sherpa> gamma([3.14,2.71])

Calculate the gamma of z=[3.14,2.71] .

Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

tools

aprates, modelflux

utilities

calc_chisqr, calc_energy_flux, calc_model_sum, calc_photon_flux, calc_source_sum, calc_stat, igam, igamc, incbet, lgam