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Plenary Lecture
High Dimensional Model Representation(s) as Multilinear Array Decomposition
Method(s)

Professor Metin Demiralp
Informatics Institute
Istanbul Technical University
ITU Bilisim Enstitusu Ayazaga Yerleskesi
Maslak, 34469, Istanbul, Turkey
E-mail: metin.demiralp@gmail.com
Abstract:
The multilinear array decomposition is an intensely investigated area today.
Although it is mostly used for three index arrays some other higher
dimensional applications are also encountered. There are different
approaches to this end although the most preferable one is the singular
value decomposition’s multilinear counterpart. It aims to decompose the
multilinear array under consideration to a sum over outer products composed
of more than two factors. The construction is based on the suppression of
the Euclidean distance between the approximant and the target array by
finding optimal values for the proposed unknown entities. The decomposition
attempts to additively represent the target array in terms of lower rank
arrays. This type methods present quite nonlinear problems as long as the
products appearing in additive representation contain more than two unknown
factors. This happens when the multilinear dimensionality (the number of the
indexes) is at least three. However, by keeping the number of each product’s
unknown factors in the representation equal to two one can use the standard
linear algebraic spectral tools to determine the unknowns. The author and
Emre Demiralp (author’s son, PhD student in cognitive neuroscience program
of the Psychology Department in University of Michigan at Ann Arbor) started
to deal with the development of such decomposition methods in last two
years. The purpose was and still is to find some ways which bypasses certain
technical and sometimes conceptual difficulties encountered in the
employment of the standing methods. Their inspiration resources were
basically high dimensional model representation which was developed in last
two decades and the fluctuation free matrix representation as a recently
developed efficient approximation tool. Their efforts take the fruits in
certain applications and now new openings seem to be appearing in the
horizon.
High dimensional model representation (HDMR) and its quite new extension,
Enhanced Multivariance Product Representation (EMPR) developed by the author
can also be used as a decomposition method if the target function is
considered as a data set given on the nodes of an orthonormal hyperprismatic
grid and discrete geometry is utilized.
HDMR can be considered as a particular case of an additive representation
over the single factor products. The terms are ordered in ascending
multivariance. EMPR, on the other hand, uses products, each of which
contains same number of univariate factors within a one-to-one relation to
the independent variables (indexes in the discrete case). However, this
increasing number of factors is balanced by keeping the number of unknowns
in each product just as 1 for easy determination. The given factors have
certain common properties also and we call them “supports” since one can
control the approximation quality even in the very crude cases of constant
or univariate level truncations.
Speech focuses on certain details of these issues by referring the original
findings of the author and his group.
Brief Biography of the Speaker:
Metin Demiralp was born in Turkey on 4 May 1948. His education from
elementary school to university was entirely in Turkey. He got his BS, MS,
and PhD from the same institution, Istanbul Technical University. He was
originally chemical engineer, however, through theoretical chemistry,
applied mathematics, and computational science years he was mostly working
on methodology for computational sciences and he is continuing to do so. He
has a group (Group for Science and Methods of Computing) in Informatics
Institute of Istanbul Technical University (he is the founder of this
institute). He collaborated with the Prof. Herschel A. Rabitz’s group at
Princeton University (NJ, USA) at summer and winter semester breaks during
the period 1985–2003 after his 14 months long postdoctoral visit to the same
group in 1979–1980.
Metin Demiralp has more than 70 papers in well known and prestigious
scientific journals, and, more than 110 contributions to the proceedings of
various international conferences. He has given many invited talks in
various prestigious scientific meetings and academic institutions. He has a
good scientific reputation in his country and he is the full member of
Turkish Academy of Sciences since 1994. He is also a member of European
Mathematical Society and the chief–editor of WSEAS Transactions on
Mathematics currently. He has also two important awards of Turkish
scientific establishments.
The important recent focii in research areas of Metin Demiralp can be
roughly listed as follows: Fluctuation Free Matrix Representations, High
Dimensional Model Representations, Space Extension Methods, Data Processing
via Multivariate Analytical Tools, Multivariate Numerical Integration via
New Efficient Approaches, Matrix Decompositions, Quantum Optimal Control.
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