sdDiff is a function based on the difference operator (or difference order for HALL method) estimating the time-series standard deviation.
The estimation works for time-series generated by Gaussian
random variables with constant standard deviation and multiple changes in mean.
Three estimators are available:
HALL : the so-called HALL-estimator of order 3. For more details see: (1990) Asymptotically optimal difference-based estimation of variance in nonparametric regression. Authors: Hall, Peter and Kay, JW and Titterinton, DM. Biometrika, pages 521--528
MAD : the median absolute deviation estimator computed on diff(x)/sqrt(2) with x the vector of datapoints
SD : the standard deviation estimator (function sd) computed on diff(x)/sqrt(2) with x the vector of datapoints