Abstract: This is a revised and updated version of the package GammaCHI. The package includes routines for computing and inverting the gamma and chi-square cumulative distribution functions (central and noncentral). Additionally, the package also provides routines for computing the gamma function, the error function and other functions related to the gamma function (the logarithm of the gamma function, the regulated gamma function and the ratio of two gamma functions). In this new version, the range of computation of the inversion routine of the central gamma distribution function invcdfgamC(ichi,a,p,q,x,ierr) is extended; p or q input values close to the underflow limit are now allowed.

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