CorrR                   This function obtains the correlation matrix of
                        longitudinal data
cv.interep              k-folds cross-validation for interep
dat                     simulated data for demonstrating the features
                        of interep
dmcp                    This function obtains the first derivative
                        function of MCP (Minimax Concave Penalty)
interep                 fit a generalized estimating equation with
                        given lambda
reformat                This function changes the format of the
                        longitudinal data from wide format to long
                        format
