Separation of stationary and non-stationary sources with a generalized eigenvalue problem

  • Authors:
  • Satoshi Hara;Yoshinobu Kawahara;Takashi Washio;Paul Von BüNau;Terumasa Tokunaga;Kiyohumi Yumoto

  • Affiliations:
  • Institute of Scientific and Industrial Research (ISIR), Osaka University, Osaka, 5670047, Japan;Institute of Scientific and Industrial Research (ISIR), Osaka University, Osaka, 5670047, Japan;Institute of Scientific and Industrial Research (ISIR), Osaka University, Osaka, 5670047, Japan;Machine Learning Group, Berlin Institute of Technology, Franklinstr, 28/29, 10587, Berlin, Germany;Meiji Institute for Advanced Study of Mathematical Sciences, Meiji University, Kanagawa, 2148571, Japan;Space Environment Research Center, Kyushu University, Fukuoka, 8128581, Japan

  • Venue:
  • Neural Networks
  • Year:
  • 2012

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Abstract

Non-stationary effects are ubiquitous in real world data. In many settings, the observed signals are a mixture of underlying stationary and non-stationary sources that cannot be measured directly. For example, in EEG analysis, electrodes on the scalp record the activity from several sources located inside the brain, which one could only measure invasively. Discerning stationary and non-stationary contributions is an important step towards uncovering the mechanisms of the data generating system. To that end, in Stationary Subspace Analysis (SSA), the observed signal is modeled as a linear superposition of stationary and non-stationary sources, where the aim is to separate the two groups in the mixture. In this paper, we propose the first SSA algorithm that has a closed form solution. The novel method, Analytic SSA (ASSA), is more than 100 times faster than the state-of-the-art, numerically stable, and guaranteed to be optimal when the covariance between stationary and non-stationary sources is time-constant. In numerical simulations on wide range of settings, we show that our method yields superior results, even for signals with time-varying group-wise covariance. In an application to geophysical data analysis, ASSA extracts meaningful components that shed new light on the Pi 2 pulsations of the geomagnetic field.