2 research outputs found
Symbolic Analysis-based Reduced Order Markov Modeling of Time Series Data
This paper presents a technique for reduced-order Markov modeling for compact
representation of time-series data. In this work, symbolic dynamics-based tools
have been used to infer an approximate generative Markov model. The time-series
data are first symbolized by partitioning the continuous measurement space of
the signal and then, the discrete sequential data are modeled using symbolic
dynamics. In the proposed approach, the size of temporal memory of the symbol
sequence is estimated from spectral properties of the resulting stochastic
matrix corresponding to a first-order Markov model of the symbol sequence.
Then, hierarchical clustering is used to represent the states of the
corresponding full-state Markov model to construct a reduced-order or size
Markov model with a non-deterministic algebraic structure. Subsequently, the
parameters of the reduced-order Markov model are identified from the original
model by making use of a Bayesian inference rule. The final model is selected
using information-theoretic criteria. The proposed concept is elucidated and
validated on two different data sets as examples. The first example analyzes a
set of pressure data from a swirl-stabilized combustor, where controlled
protocols are used to induce flame instabilities. Variations in the complexity
of the derived Markov model represent how the system operating condition
changes from a stable to an unstable combustion regime. In the second example,
the data set is taken from NASA's data repository for prognostics of bearings
on rotating shafts. We show that, even with a very small state-space, the
reduced-order models are able to achieve comparable performance and that the
proposed approach provides flexibility in the selection of a final model for
representation and learning.Comment: 21 pages, 12 figure
Markov Modeling of Time-Series Data using Symbolic Analysis
Markov models are often used to capture the temporal patterns of sequential
data for statistical learning applications. While the Hidden Markov
modeling-based learning mechanisms are well studied in literature, we analyze a
symbolic-dynamics inspired approach. Under this umbrella, Markov modeling of
time-series data consists of two major steps -- discretization of continuous
attributes followed by estimating the size of temporal memory of the
discretized sequence. These two steps are critical for the accurate and concise
representation of time-series data in the discrete space. Discretization
governs the information content of the resultant discretized sequence. On the
other hand, memory estimation of the symbolic sequence helps to extract the
predictive patterns in the discretized data. Clearly, the effectiveness of
signal representation as a discrete Markov process depends on both these steps.
In this paper, we will review the different techniques for discretization and
memory estimation for discrete stochastic processes. In particular, we will
focus on the individual problems of discretization and order estimation for
discrete stochastic process. We will present some results from literature on
partitioning from dynamical systems theory and order estimation using concepts
of information theory and statistical learning. The paper also presents some
related problem formulations which will be useful for machine learning and
statistical learning application using the symbolic framework of data analysis.
We present some results of statistical analysis of a complex thermoacoustic
instability phenomenon during lean-premixed combustion in jet-turbine engines
using the proposed Markov modeling method