et al., 2017] for an overview. While DL provides a basis
for prediction given a set of descriptive features, the issue
of how to detect and quantify co-movements remains to be
addressed. This paper suggests the use of recurrence analysis
based on Cross Recurrence Plots (CRP) for detecting and
extracting features indicative of stocks’ shared dynamics or
co-movements, along with a deep learning framework for
predicting whether certain pairs of stocks will exhibit a shared
dynamics in the future (in the sense specified in Section
II). Not only in the view of extending the ML and applied
econometrics literature in this direction, but the possibility of
forecasting epochs of time series synchronization is likewise
relevant for practitioners.
For detecting and quantifying co-movements or more gen-
erally shared dynamical features in time series, the standard
econometric approach is that of cross-correlation analysis,
e.g., [Tsay, 2005, Chapter 8]. This intuitive linear approach,
based on the estimation and perhaps forecasting of cross-
correlation matrices, appears to be an element of a much wider
theory and methodological approach that has been explored
and developed in the last years within a broader generic non-
financial setting. Simple cross-correlation analysis has been
remarkably extended and generalized towards methods that
help explore co-movements between time series within non-
linear, noisy, and non-stationary systems of very complex
dynamics, either financial [Ma et al., 2013], [Bonanno et al.,
2001], [Ramchand and Susmel, 1998] or not [Webber Jr. and
Zbilut, 1994], [Marwan and Kurths, 2002], [Lancia et al.,
2014].
Recurrent analysis [Webber and Marwan, 2015] explores the
reconstruction of a phase-space using time-delay embedding
for quantifying characteristics of nonlinear patterns in a time
series over time [Takens, 1981]. This is done by calculating
the so-called Recurrence Plot [Eckmann et al., 1995], the core
concept of which is to identify all points in time that the
phase-space trajectory of a single time series visits roughly
the same area in the phase-space. Recurrence plot analysis has
no assumptions or limitations on dimensionality, distribution,
stationarity, and size of data [Webber and Marwan, 2015].
These characteristics make it suitable for multidimensional
and non-stationary financial time series data analysis. The
CRP [Marwan, 1999] is an extension of the recurrence plot,
introduced to analyze the co-movement and synchronization
of two different time series. The CRP indicates points in
time that a time series visits the state of another time series,
with possibly different lengths in the same phase-space. These
concepts are discussed in further detail in Section II.
In this paper, we propose a method for predicting the state of
synchronization over time of two multidimensional 2financial
time series based on their CRP. In particular, we use the
2Throughout the paper, with uni- or multi- variate we refer to the nature of
the analyses (RP as opposed to CRP), and with one- or multi- dimensional we
refer to the nature of the time series. That is, the RP (as presented in equation
(2)) provides a univariate analysis of a single one-dimensional time series,
while the CRP (as presented in latter equation (3)) a multivariate analysis of
two one-dimensional or multi-dimensional time series.
CRP to quantify the co-movements and extract the binary
representation of its diagonal elements as the prediction targets
for a DL model. For predicting the state of synchronization
at the next epoch we employ a Convolutional Neural Network
(CNN) that uses as inputs CRPs independently calculated from
data-crops obtained by applying fixed-size sliding windows on
the time series. Our extensive experiments on 12 stocks of
the S&P100 index selected from different sectors show that
the proposed method can predict the synchronization of stock
pairs with satisfactory performance.
The remainder of the paper is organized as follows. Section
II introduces in detail the concepts and theory behind the CRP,
with an outlook on its applications in financial and economic
problems. Our proposed approach for predicting time instances
of time series’ synchronization is presented in Section III.
Empirical results on real market data are provided in Section
IV, whilst Section V provides conclusions.
II. FINANCIAL TIME SERIES RECURRENCE ANALYSIS
Recurrence in the analysis of time series, seen as a nonlinear
dynamic system, is the repetition of a pattern over time. The
visualization of recurrences in the dynamics of a time series
can be expressed via a RP or recurrence matrix [Webber
and Marwan, 2015]. In other words, the RP represents the
recurrence of the phase-space trajectory to a state. The phase-
space of a d-dimensional time series Nwith Tobservations
N={n>
1,n>
2,...,n>
T}>, with nibeing the row-vector
representing a generic observation at time i,i= 1, . . . , T is
calculated using the time-delay embedding method. State Ni
in the phase-space is obtained by
Ni= [ni,ni+τ,...,ni+(k−1)τ], i = 1, . . . , T 0, (1)
where τdenotes the delay and kis the embedding dimension,
T0=T−τ(k−1),τand kcan, respectively, be determined
with the Average Mutual Information Function (AMI) method
[Fraser and Swinney, 1986] and the False Nearest Neighbors
(FNN) method of [Kennel et al., 1992]. For a uni-dimensional
time series Niis a row vector of size (1 ×k), for a d-
dimensional times series Niis a row vector of size (1 ×kd).
The recurrence state matrix of the reconstructed phase-space,
known as Recurrence Plot (RP), at times iand j, is defined
as
Ri,j (ε) = H(ε− kNi−Njk), i, j = 1, . . . , T 0, (2)
where εis a threshold distance value, H(·)is the Heaviside
function, and k·k is the euclidean distance. Due to the
underlying embedding (1), Ri,j is defined for i i= 1 up
to T0=T−τ(k−1). If two states Niand Njare in an
ε-neighbourhood the value of Ri,j is equal to 1, otherwise is
0.The value of εhighly affects the output of RP. When εis too
small or too large, the RP cannot identify the true recurrence
of states. There are different approaches for finding the best
value for εin the literature [Webber and Marwan, 2015]. We
follow the guidelines provided in [Schinkel et al., 2008] for
selecting ε. The values on the diagonal line of RP are equal
to one (i.e., Ri,i = 1) because in that case the two states