This package does changepoint analysis for both abrupt and gradual

change models, by fitting an S-curve using nonlinear least squares.

Currently just a single changepoint is analyzed, but this can easily be

generalized using the "binary segmentation" method. Code for this will

be added in the near future.

In the case of abrupt models, the S-curve is used to approximate a step

function. The user specifies a steep slope for this. For gradual

models, the slope will be estimated by the algorithm.

Output consists of the changepoint location, the pre- and post-mean

levels, and for the gradual case, the slope. Standard errors (and

covariance matrix) are supplied for all estimated parameters, by calling

vcov() on the output.