I'm reading this text and there is a simple toy example on page 3:
$$H(S_1), H(S_2), H(S_3) \sim \operatorname{Dir}(\alpha \operatorname{erf}(-1), \alpha(\operatorname{erf}(1)-\operatorname{erf}(-1)), \alpha(1 - \operatorname{erf}(1)))$$
The Dirichlet distribution takes positive arguments but $\operatorname{erf}(-1)$ is a negative number and is thus not a valid parameter.
I assume $\operatorname{erf}$ is the error function as described in Wikipedia
Did I misinterpret the meaning of $\operatorname{erf}$?