The TISEAN project has emerged from work of the involved research groups over several years. Some of the programs are in fact based on code published in Ref. [2]. Nevertheless, we still like to see it as a starting point rather than a conclusive step. First of all, nonlinear time series analysis is still a rapidly evolving field, in particular with respect to applications. This implies that the selection of topics in this article and the selection of algorithms implemented in TISEAN are highly biased towards what we know now and found useful so far. But even the well established concepts like dimension estimation and noise reduction leave considerable room for alternatives to the present implementation. Sometimes this resulted in two or more concurring and almost redundant programs entering the package. We have deliberately not eliminated these redundancies since the user may benefit from having a choice. In any case it is healthy to know that for most of the algorithms the final word hasn't been spoken yet - nor is ever to be.

While the TISEAN package does contain a number of tools for *linear*
time series analysis (spectrum, autocorrelations, histograms, etc.), these are
only suitable for a quick inspection of the data. Spectral or even ARMA
estimation are industries in themselves and we refer the reader - and the user
of TISEAN - to the existing literature and available statistics software
for optimal, up-to-date implementations of these important methods.

Some users will miss a convenient graphical interface to the programs. We felt that at this point the extra implementational effort would not be justified by the expected additional functionality of the package. Work is in progress, however, to provide interfaces to higher level mathematics (or statistics) software.

Wed Jan 6 15:38:27 CET 1999