Abstract
Examples of complex-valued random phenomena in science and engineering are abound, and joint blind source separation (JBSS) provides an effective way to analyze multiset data. Thus there is a need for flexible JBSS algorithms for efficient data-driven feature extraction in the complex domain. Independent vector analysis (IVA) is a prominent recent extension of independent component analysis to multivariate sources, i.e., to perform JBSS, but its effectiveness is determined by how well the source models used match the true latent distributions and the optimization algorithm employed. The complex multivariate generalized Gaussian distribution (CMGGD) is a simple, yet effective parameterized family of distributions that account for full second- and higher-order statistics including noncircularity, a property that has been often omitted for convenience. In this paper, we marry IVA and CMGGD to derive, IVA-CMGGD, with a number of numerical optimization implementations including steepest descent, the quasi-Newton method Broyden–Fletcher–Goldfarb–Shanno (BFGS), and its limited-memory sibling limited-memory BFGS all in the complex-domain. We demonstrate the performance of our algorithm on simulated data as well as a 14-subject real-world complex-valued functional magnetic resonance imaging dataset against a number of competing algorithms.
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Unitary up to a factor of 2 implies \({\mathbf {T}}{\mathbf {T}}^H={\mathbf {T}}^H{\mathbf {T}} = 2{\mathbf {I}}\).
The classical singular value decomposition is sufficient to obtain the noncircularity coefficients. However, if the corresponding canonical projections are needed, a special, complex-symmetric decomposition called the Takagi factorization (Horn and Johnson 1990; Schreier and Scharf 2010; Moreau and Adalı 2013) is required to maintain the complex augmented form.
We maintain unit-norm rows of \({\mathbf {W}}\) to prevent driving the cost function lower through scaling alone.
For the conjugate gradient method, not discussed in this paper, the value of \(c_2\) is often taken to be 0.1 (Nocedal and Wright 2006).
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Acknowledgements
The hardware used in the computational studies is part of the UMBC High Performance Computing Facility (HPCF). The facility is supported by the U.S. National Science Foundation through the MRI program (Grant Nos. CNS-0821258, CNS-1228778, OAC-1726023, 1618551 and 1631838) and the SCREMS program (Grant No. DMS-0821311), with additional substantial support from the University of Maryland, Baltimore County (UMBC). See hpcf.umbc.edu for more information on HPCF and the Projects using its resources.
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Appendices
Appendix
Derivation of gradient
Since (15) is a real-valued function of complex variables, it suffices to compute the gradient with respect to \({\mathbf {w}}_n^{[k]*}\) using Wirtinger calculus. First, by applying the chain rule we can write:
Due to (12), the first term in (28) is equal to 0 leaving only the second term. Next, we subdivide the IVA-CMGGD cost function in (15) into two terms:
where
and
Differentiating \(J_1({\mathbf {W}})\) yields:
where \({\mathbf {e}}_k\) is defined as in (16) and \(\frac{\partial {\mathbf {y}}_n^{*}}{\partial {\mathbf {w}}_n^{[k]*}}={\mathbf {x}}^{[k]*}\).
In order to differentiate \(J_2({\mathbf {W}})\), we utilize a decoupling procedure (Anderson et al. 2012a), originally established in Li and Zhang (2007). The purpose is to factorize each summand in (31) into the product of two terms: one dependent on \({\mathbf {w}}_n^{[k]}\) and the other independent of it. By defining \(\tilde{{\mathbf {W}}}_n^{[k]}\) to be the \((N-1)\times N\) matrix containing rows of \({\mathbf {W}}^{[k]}\) other than the nth, and by defining
the decoupling procedure admits the following representation for \(J_2({\mathbf {W}})\):
where \({\mathbf {h}}_n^{[k]}\) is a unit-length vector orthogonal to each of \(\left\{ {\mathbf {w}}_n^{[m]}\right\} _{m\ne k}\). Then, the gradient of \(J_2({\mathbf {W}})\) can be computed as:
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Mowakeaa, R., Boukouvalas, Z., Long, Q. et al. IVA using complex multivariate GGD: application to fMRI analysis. Multidim Syst Sign Process 31, 725–744 (2020). https://doi.org/10.1007/s11045-019-00685-0
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DOI: https://doi.org/10.1007/s11045-019-00685-0