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.

Both single- and multiple-changepoint models are allowd.

In the case of abrupt models, an 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.