Give access to all the implemented algorithms through the third argument. The
last argument is a structure with two fields `large` and `small`. The first
field specifies the algorithm to be used for α>1 while the second field defines
the algorithm to be used for α ∈ (0,1).
Default algorithms are:
- Cheng (1977) for α>1,
- Johnk (1964) α ∈ (0,1).
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