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Introduction

Module by: C. Sidney Burrus. E-mail the author

Summary: Overview of the use of a matrix times a vector for the description of signal and systems operations. The vectors are descriptions of the signals and the matrix operator is a description of the system.

Introduction

The tools, ideas, and insights from linear algebra, abstract algebra, and functional analysis can be extremely useful to signal processing and system theory in various areas of engineering, science, and social science. Indeed, many important ideas can be developed from the simple operator equation

A x = b A x = b
(1)

by considering it in a variety of ways. If xx and bb are vectors from the same or, perhaps, different vector spaces and AA is an operator, there are three interesting questions that can be asked which provide a setting for a broad study.

  1. Given AA and xx , find bb . The analysis or operator problem or transform.
  2. Given AA and bb , find xx . The inverse or control problem or deconvolution or design.
  3. Given xx and bb , find AA . The synthesis or design problem or parameter identification.

Much can be learned by studying each of these problems in some detail. We will generally look at the finite dimensional problem where Equation 1 can more easily be studied as a finite matrix multiplication [19], [20], [16], [21]

a 11 a 12 a 13 a 1 N a 21 a 22 a 23 a 31 a 32 a 33 a M 1 a M N x 1 x 2 x 3 x N = b 1 b 2 b 3 b M a 11 a 12 a 13 a 1 N a 21 a 22 a 23 a 31 a 32 a 33 a M 1 a M N x 1 x 2 x 3 x N = b 1 b 2 b 3 b M
(2)

but will also try to indicate what the infinite dimensional case might be [11], [22], [18], [17].

An application to signal theory is in [10], to optimization [15], and multiscale system theory [6]. The inverse problem (number 2 above) is the basis for a large study of pseudoinverses, approximation, optimization, filter design, and many applications. When used with the l2l2 norm [14], [5] powerful results can be optained analytically but used with other norms such as ll, l1l1, l0l0 (a pseudonorm), an even larger set of problems can be posed and solved [1], [3].

A development of vector space ideas for the purpose of presenting wavelet representations is given in [7], [2]. An interesting idea of unconditional bases is given by Donoho [8].

Linear regression analysis can be posed in the form of Equation 1 and Equation 2 where the MM rows of AA are the vectors of input data from MM experiments, entries of xx are the NN weights for the NN components of the inputs, and the MM values of bb are the outputs [1]. This can be used in machine learning problems [4], [12]. A problem similar to the design or synthesis problem is that of parameter identification where a model of some system is posed with unknown parameters. Then experiments with known inputs and measured outputs are run to identify these parameters. Linear regression is also an example of this [1], [4].

Dynamic systems are often modelled by ordinary differential equation where bb is set to be the time derivative of xx to give what are called the linear state equations:

x ˙ = A x x ˙ = A x
(3)

or for difference equations and discrete-time or digital signals,

x ( n + 1 ) = A x ( n ) x ( n + 1 ) = A x ( n )
(4)

which are used in digital signal processing and the analysis of certain algorithms. State equations are useful in feedback control as well as in simulation of many dynamical systems and the eigenvalues and other properties of the square matix AA are important indicators of the performance [23], [9].

The ideas of similarity transformations, diagonalization, the eigenvalue problem, Jordon normal form, singular value decomposition, etc. from linear algebra [19], [20], [13] are applicable to this problem.

Various areas in optimization and approximation use vector space math to great advantage [15], [14].

This booklet is intended to point out relationships, interpretations, and tools in linear algebra, matrix theory, and vector spaces that scientists and engineers might find useful. It is not a stand-alone linear algebra book. Details, definitions, and formal proofs can be found in the references. A very helpful source is Wikipedia.

There is a variety software systems to both pose and solve linear algebra problems. A particularly powerful one is Matlab [16] which is, in some ways, the gold standard since it started years ago a purely numerical matrix package. But there are others such as Octave, SciLab, LabVIEW, Mathematica, Maple, etc.

References

  1. Albert, Arthur. (1972). Regression and the Moore-Penrose Pseudoinverse. New York: Academic Press.
  2. Burrus, C. Sidney and Gopinath, Ramesh A. and Guo, Haitao. (1998). Introduction to Wavelets and the Wavelet Transform. [to appear on the web in Connexions: cnx.org]. Upper Saddle River, NJ: Prentice Hall.
  3. Ben-Israel, Adi and Greville, T. N. E. (1974). Generalized Inverses: Theory and Applications. [Second edition, Springer, 2003]. New York: Wiley and Sons.
  4. Bishop, Christopher M. (2006). Pattern Recognition and Machine Learning. Springer.
  5. Björck, Åke. (1996). Numerical Methods for Least Squares Problems. Philadelphia: Blaisdell, Dover, SIAM.
  6. Benveniste, A. and Nikoukhah, R. and Willsky, A. S. (1994, January). Multiscale System Theory. IEEE Transactions on Circuits and Systems, I, 41(1), 2–15.
  7. Daubechies, Ingrid. (1992). Ten Lectures on Wavelets. [Notes from the 1990 CBMS-NSF Conference on Wavelets and Applications at Lowell, MA]. Philadelphia, PA: SIAM.
  8. Donoho, David L. (1993, December). Unconditional Bases are Optimal Bases for Data Compression and for Statistical Estimation. [Also Stanford Statistics Dept. Report TR-410, Nov. 1992]. Applied and Computational Harmonic Analysis, 1(1), 100–115.
  9. DeRusso, Paul M. and Roy, Rob J. and Close, Charles M. (1965). State Variables for Engineers. [Second edition 1997]. Wiley.
  10. Franks, Lewis. (1969). Signal Theory. Englewood Cliffs, NJ: Prentice–Hall.
  11. Halmos, Paul R. (1958). Finite-Dimensional Vector Spaces. [Springer 1974]. Princeton, NJ: Van Nostrand.
  12. Haykin, Simon O. (2008). Neural Networks and Learning Machines. Prentice Hall.
  13. Hefferon, Jim. (2011). Linear Algebra. [Copyright: cc-by-sa, URL:joshua.smcvt.edu]. Virginia Commonwealth Univeristy Mathematics Textbook Series.
  14. Lawson, C. L. and Hanson, R. J. (1974). Solving Least Squares Problems. [Second edition by SIAM in 1987]. Inglewood Cliffs, NJ: Prentice-Hall.
  15. Luenberger, D. G. (1969, 1997). Optimization by Vector Space Methods. New York: John Wiley & Sons.
  16. Moler, Cleve. (2008). Numerical Computing with MATLAB. [available: http://www.mathworks.com/moler/]. South Natick, MA: The MathWorks, Inc.
  17. Moon, Todd K. and Stirling, Wynn C. (2000). Mathematical Methods and Algorithms for Signal Processing. Upper Saddle River, NJ: Prentice-Hall.
  18. Oden, J. Tinsley and Demkowicz, Leszek F. (1996). Applied Functional Analysis. Boca Raton: CRC Press.
  19. Strang, Gilbert. (1976). Linear Algebra and Its Applications. [4th Edition, Brooks Cole, 2005]. New York: Academic Press.
  20. Strang, Gilbert. (1986). Introduction to Linear Algebra. [4th Edition, 2009]. New York: Wellesley Cambridge.
  21. Trefethen, Lloyd N. and III, David Bau. (1997). Numerical Linear Algebra. SIAM.
  22. Young, R. M. (1980). An Introduction to Nonharmonic Fourier Series. New York: Academic Press.
  23. Zadeh, Lotfi A. and Desoer, Charles A. (1963, 2008). Linear System Theory: The State Space Approach. Dover.

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