# American Institute of Mathematical Sciences

December  2020, 7(2): 209-241. doi: 10.3934/jcd.2020009

## An incremental approach to online dynamic mode decomposition for time-varying systems with applications to EEG data modeling

 Electrical and Computer Engineering Department, Michigan State University, East Lansing, MI 48824, USA

Received  September 2019 Published  July 2020

Fund Project: This work has been supported by NSF Award IIS-1734272

Dynamic Mode Decomposition (DMD) is a data-driven technique to identify a low dimensional linear time invariant dynamics underlying high-dimensional data. For systems in which such underlying low-dimensional dynamics is time-varying, a time-invariant approximation of such dynamics computed through standard DMD techniques may not be appropriate. We focus on DMD techniques for such time-varying systems and develop incremental algorithms for systems without and with exogenous control inputs. We build upon the work in [35] to scenarios in which high dimensional data are governed by low dimensional time-varying dynamics. We consider two classes of algorithms that rely on (ⅰ) a discount factor on previous observations, and (ⅱ) a sliding window of observations. Our algorithms leverage existing techniques for incremental singular value decomposition and allow us to determine an appropriately reduced model at each time and are applicable even if data matrix is singular. We apply the developed algorithms for autonomous systems to Electroencephalographic (EEG) data and demonstrate their effectiveness in terms of reconstruction and prediction. Our algorithms for non-autonomous systems are illustrated using randomly generated linear time-varying systems.

Citation: Mustaffa Alfatlawi, Vaibhav Srivastava. An incremental approach to online dynamic mode decomposition for time-varying systems with applications to EEG data modeling. Journal of Computational Dynamics, 2020, 7 (2) : 209-241. doi: 10.3934/jcd.2020009
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Topographical view for EEG channels with the channel FCz, where the ErrPs can be characterized, marked in red bold font
The average response to an event at $t = 0$: the mean ERP (confidence level = $95\%$) at the FCz channel (left panel) and the topographical view for brain activity across all channels (right panel). The top and middle panels show the patterns during the correct event and the erroneous event, respectively. The bottom panel shows that ErrP obtained by subtracting the signal associated with the correct event from that of the erroneous event. The topographical views are shown at the three characterizing peaks that occur at $200$ msec, $260$ msec, and $360$ msec, respectively
The mean of the normalized RMS prediction error computed over all iterations as well as the associated 95% confidence sets for (a) correct events and (b) erroneous events
Normalized RMS error for a future-window of $64$ samples of EEG states at channel FCz using incremental DMD with $\sigma_{\text{thr}} = 0.01$ (left panel), incremental DMD with $\sigma_{\text{thr}} = 0.001$ (middle panel), and online DMD (right panel) for (a) correct event, and (b) erroneous event
Predicted ERP signal at channel FCz using incremental DMD with $\sigma_{\text{thr}} = 0.01$ (left panel), incremental DMD with $\sigma_{\text{thr}} = 0.001$ (middle panel), and online DMD (right panel) for (a) correct event, and (b) erroneous event
Normalized RMS error for the predicted ERP signal at channel FCz for correct events (left panel) and erroneous events (right panel), using (a) incremental DMD, and (b) online DMD
Normalized RMS error of ERP prediction using weighted incremental DMD with initial window of $128$ samples during (a) correct event, and (b) Erroneous event
Normalized RMS error of ERP prediction using windowed incremental DMD with different window sizes during (a) correct event, and (b) Erroneous event
The predicted ERP signal at channel FCz based on well conditioned EEG datasets using incremental DMD model (left panel) and online DMD model (right panel) during (a) correct events and (b) erroneous events
Topographical views for the real part part of the $4$ dominant DMD modes during correct events using threshold values of (a) $\sigma_{\text{thr}} = 0.01$, and (b) $\sigma_{\text{thr}} = 0.001$
Topographical views for the real part of the $4$ dominant DMD modes during erroneous events using threshold values of (a) $\sigma_{\text{thr}} = 0.01$, and (b) $\sigma_{\text{thr}} = 0.001$
The left panel show the continuous time DMD eigenvalues for $\sigma_{\text{thr}} = 0.01$ and the right panel shows the continuous time DMD eigenvalues for $\sigma_{\text{thr}} = 0.001$ during (a) correct events (b) erroneous events
Reconstructed ERP signal at channel FCz using incremental DMD with $\sigma_{thr} = 0.01$ (left panel), incremental DMD with $\sigma_{thr} = 0.001$ (middle panel), and online DMD (right panel) for (a) correct events and (b) erroneous events.
Normalized RMS error for the reconstructed ERP signal at channel FCz for correct events (left panel) and erroneous events (right panel), using (a) incremental DMD, and (b) online DMD
The Frobenius norm of prediction error for a future-window of 10 samples using (a) weighted incremental DMD (red line) and weighted incremental DMDc(blue line), and (b) windowed incremental DMD (red line) and windowed incremental DMDc (blue line)
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