This function calculates HD-D, an idealized version of
vocd-d (see McCarthy & Jarvis, 2007). In contrast to
lex.div, which by default
calculates all possible measures and their progressing
characteristics, this function will only calculate the
HD-D value, and characteristics are off by default.
References
McCarthy, P.M. & Jarvis, S. (2007). vocd: A theoretical
and empirical evaluation. Language Testing, 24(4),
459--488.