Function name: zip.mle
Description:

Instead of maximising the log-likelihood via a numerical optimiser we used a Newton-Raphson algorithm which is faster. See wikipedia for the equation to be solved in the case of the zero inflated distribution. https://en.wikipedia.org/wiki/Zero-inflated_model. In order to avoid negative values we have used link functions, log for the \eqn{lambda} and logit for the pi as suggested by Lambert (1992). As for the zero truncated Poisson see https://en.wikipedia.org/wiki/Zero-truncated_Poisson_distribution. }

Authors: Author: Michail Tsagris and Manos Papadakis