McCullagh, P. (1980). Regression models for ordinal data. Journal of the Royal Stastical Society, Series B, 42(2), 109-142. With assist from appendix of Agresti, (1984). Agresti, A. (1984). Analysis of ordinal categorical data. New York, Wiley, p. 244-246.
McCullagh_derivative_log_l_wrt_beta(n, x, gamma)derivative
matrix of observed counts
design matrix for location
matrix of model-based cumulative logits