This function implements the getData function to
perform the online changepoint detection for the 'Mei' class.
Mei_update(x_new, R, b)a new data point
vector of of tail CUSUMs that will be tracked and updated online
a user specified lower bound on per-coordinate magnitude of the vector of change to be detected.
a list of
stat: a vector of 2 test statistics for the 'Mei' class.
R: the updated R vector
Mei, Y. (2010) Efficient scalable schemes for monitoring a large number of data streams. Biometrika, 97, 419--433.