Research projects

Project CEMAPRE internal

TitleClassification and clustering of big data time series with spectral measures (continuation for year 2020)
ParticipantsJorge Caiado, Nuno Crato (Principal Investigator)
SummaryThe big data revolution is now offering researchers and analysts new possibilities and new
challenges. This is particularly true with time series, as for many domains we now have access to
very long time series and to many time series related to a given domain of interest. This happens in
areas as diverse as astronomy, geophysics, medicine, social media, and finance.

The diversity and length of data available to researchers leads to particular challenges when
comparing and clustering time series. For these tasks it is not usually possible to use traditional
methods of analysing, estimating models, and comparing features, as these methods imply lengthy
computations, such as the inversion of extremely large matrices.

We have proposed a spectral method of synthesizing and comparing time series characteristics which
is nonparametric and focused on the data cyclical features. Instead of using all the information
available from data, which is computationally very expensive, this procedure we
will use regularization rules in order to select and summarize the most relevant information for
clustering purposes. This method does not imply the computation of the full periodograms, but only
of the periodogram components around the frequencies of interest. It then proceeds to comparing the
periodogram ordinates for the various time series and grouping them with common clustering methods.
We called it a fragmented-periodogram approach.

In 2019, we have achieved the project goals for the year and published in an international journal
the first results of our research. In 2020, we want to further disseminate our results and extend
them for situations in which the main spectral frequencies are unknown and need to be estimated.
This introduces further challenges to the fragmented-periodogram computations, as we should need to
introduce a two-step procedure.