X: A matrix of covariates with J rows and P_f + P_r columns, where the first P_f columns are connected to fixed coefficients and the last P_r columns are connected to random coefficients.
alternatives: A vector with unique integers from 1 to J, indicating the alternatives for which choice probabilities are to be computed.
parameter: An object of class RprobitB_parameter.
ordered: A boolean, FALSE per default. If TRUE, the choice set alternatives is assumed to be ordered from worst to best.
Returns
A probability vector of length length(alternatives).