Exact PDF and CDF of a sum of Gamma random variables. It uses the findings in : Imran Shafique Ansari and Ferkan Yilmaz and Mohamed-Slim Alouini and Oguz Kucur: "New Results on the Sum of Gamma Random Variates With Application to the Performance of Wireless Communication Systems over Nakagami-m Fading Channels", https://arxiv.org/abs/1202.2576 . Usage shown in main.
It also contains an implementation of the Fox's generalized H-function as described in: Saxena, R. K. "Functional relations involving generalized H-function." Le Matematiche 53.1 (1998): 123-131.