Computes the Chao species estimator for both
a vector of positive integers or zero of any length
This function is typically only called internally by the functions
chao2. The function has a built in bias correction, such that it
will not return values of infinity or non-numbers.
Estimated numer of species using the Chao estimator.
Chao, A. 1984. Nonparametric estimation of the number of classes in a population. Scandinavian Journal of Statistics 11: 265-270.
For the more useful implementations of the Chao estimator, see
chao1 for the abundance based estimator or
chao2 for the incidence based estimator
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