Translations of MATHEMATICAL MONOGRAPHS
Volume 239
Wavelet Theory
I. Ya. Novikov V. Yu. Protasov M. A. Skopina
American Mathematical Society 10.1090/mmono/239
Translations of MATHEMATICAL MONOGRAPHS
Volume 239
Wavelet Theory I. Ya. Novikov V. Yu. Protasov M. A. Skopina
Translated by Evgenia Sorokina
M THE ATI A CA M L ΤΡΗΤΟΣ ΜΗ N Ω Τ Ι Σ Ι Ε S A O
C C I
I American Mathematical Society
R E
E T
ΑΓΕΩΜΕ
Y
M A Providence, Rhode Island
F O 8 U 88 NDED 1 EDITORIAL COMMITTEE AMS Subcommittee Robert D. MacPherson Grigorii A. Margulis James D. Stasheff (Chair) ASL Subcommittee Steffen Lempp (Chair) IMS Subcommittee Mark I. Freidlin (Chair) I. . Novikov, V. . Protasov, M. A. Skopina TEORI VSPLESKOV M.: Fizmatlit, 2005 This work was originally published in Russian by Fizmatlit under the title “Teori vspleskov” c 2005. The present translation was created under license for the American Mathematical Society and is published by permission. Translated by Evgenia Sorokina
2010 Mathematics Subject Classification. Primary 42C40.
For additional information and updates on this book, visit www.ams.org/bookpages/mmono-239
Library of Congress Cataloging-in-Publication Data Novikov, I. IA. (Igor IAkovlevich), 1958– [Teoriia vspleskov. English] Wavelet theory / I. Ya. Novikov, V. Yu. Protasov, M.A. Skopina ; translated by Evgenia Sorokina. p. cm. — (Translations of mathematical monographs ; v. 239) Includes bibliographical references and index. ISBN 978-0-8218-4984-2 (alk. paper) 1. Wavelets (Mathematics) 2. Harmonic analysis. I. Protasov, V. IU. (Vladimir IUrevich), 1970– II. Skopina, M. A. (Mariia Aleksandrovna), 1958– III. Title. QA403.3.N6813 2010 515.2433—dc22 2010035110
Copying and reprinting. Individual readers of this publication, and nonprofit libraries acting for them, are permitted to make fair use of the material, such as to copy a chapter for use in teaching or research. Permission is granted to quote brief passages from this publication in reviews, provided the customary acknowledgment of the source is given. Republication, systematic copying, or multiple reproduction of any material in this publication is permitted only under license from the American Mathematical Society. Requests for such permission should be addressed to the Acquisitions Department, American Mathematical Society, 201 Charles Street, Providence, Rhode Island 02904-2294 USA. Requests can also be made by e-mail to [email protected]. c 2011 by the American Mathematical Society. All rights reserved. The American Mathematical Society retains all rights except those granted to the United States Government. Printed in the United States of America. ∞ The paper used in this book is acid-free and falls within the guidelines established to ensure permanence and durability. Visit the AMS home page at http://www.ams.org/ 10987654321 161514131211 To my beloved wife and children. I. Ya. Novikov
To my father Yurii Ivanovich Protasov who taught me to love hard sciences. V. Yu. Protasov
My mathematical dynasty was founded by my grandfather I. A. Skopin. It was further continued by my father A. I. Skopin. I dedicate this book to them. M. A. Skopina i Contents
Preface ix Chapter 1. Wavelets on the Line 1 1.1. Riesz bases 1 1.2. MRA and scaling functions 7 1.3. Wavelet spaces 15 1.4. Haar, Battle-Lemarie, Str¨omberg, and Meyer systems 23 1.5. Uncertainty constants 30 1.6. Computational algorithms 40 1.7. Convergence of wavelet expansions 42 1.8. Wavelet frames 52 Chapter 2. Multivariate Wavelets 63 2.1. Separable MRA 63 2.2. Matrix dilation 66 2.3. Nonseparable MRAs 69 2.4. Construction of refinable functions 74 2.5. Conditions of biorthogonality 79 2.6. Construction of wavelet functions 90 2.7. Wavelet bases 98 2.8. Haar MRAs 105 Chapter 3. Compactly Supported Refinable Functions 115 3.1. Existence, uniqueness, and weak convergence 115 3.2. Strang-Fix conditions 117 3.3. Approximation by shifts of refinable functions 125 3.4. Linear independence, stability, and orthogonality of integer shifts 130 3.5. Examples and applications 140 Chapter 4. Wavelets with Compact Support 143 4.1. Construction of orthogonal wavelets 143 4.2. Wavelets generated by a compactly supported scaling function 152 4.3. Time-frequency localization 156 4.4. Asymptotics of zeros of Bernstein’s polynomials 175 Chapter 5. Fractal Properties of Wavelets 191 5.1. Refinable functions and fractal curves 191 5.2. Fractal curves in the space Lp 198 r r 5.3. Smoothness of fractal curves in the spaces Wp and C 200 5.4. Local smoothness of fractal curves 204 5.5. Examples 216
v vi CONTENTS
Chapter 6. Factorization of Refinement Equations 219 6.1. Operators corresponding to the clean mask 219 6.2. Mask cleaning procedure 222 6.3. Space A˜n and the general form of the operators T0,T1 on it 226 6.4. Factorization theorems 231
Chapter 7. Smoothness of Compactly Supported Wavelets 233 7.1. Matrix method 233 7.2. Local smoothness of wavelets 236 7.3. Special cases and examples 241 7.4. Method of pointwise estimation of the Fourier transform 256 7.5. Estimation by invariant cycles 262
Chapter 8. Nonstationary Wavelets 271 8.1. General theory of nonstationary wavelets 271 8.2. Nonstationary infinitely differentiable orthonormal wavelets with compact support 280 8.3. Decay rate of the Fourier transforms of elements of a nonstationary scaling sequence 288 8.4. Uncertainty constants for Ψ 294 8.5. Nonstationary wavelets with modified Daubechies masks 299 8.6. Uncertainty constants for Ψa 302 8.7. Nonstationary wavelets bases in Sobolev spaces 305
Chapter 9. Periodic Wavelets 315 9.1. PMRA and scaling sequence 315 9.2. Construction of wavelet functions 325 9.3. Wavelet packets 330 9.4. Generating function 332 9.5. Kotelnikov-Shannon system 338
Chapter 10. Approximation by Periodic Wavelets 345 10.1. Convergence of wavelet expansions in norm 345 10.2. Convergence of wavelet expansions almost everywhere 349 10.3. Direct and inverse theorems 358 10.4. Convergence of wavelet expansions at a point 370
Chapter 11. Remarkable Properties of Wavelet Bases 381 11.1. Unconditional wavelet bases 381 11.2. Optimal polynomial bases in the space C(T) 390 11.3. Optimal polynomial bases in the space C[−1, 1] 393 11.4. Wavelet bases in Besov and Lizorkin-Triebel spaces 407 11.5. Linear operators in the Lizorkin-Triebel spaces 431
Appendix A. Auxiliary Facts of the Theory of Functions and Functional Analysis 453 A.1. Bases 453 A.2. Linear functionals in normed spaces 454 A.3. Distributions 455 A.4. Marcinkiewicz interpolation theorem 458 CONTENTS vii
A.5. Spectral radius 458 A.6. Joint spectral radius and the Lyapunov exponent 459 A.7. Smoothness and the decay rate of the Fourier transform 462 A.8. Wiener theorem for L2 464 A.9. Lebesgue sets 465 A.10. Absolutely continuous functions 469 A.11. Nonnegative trigonometric polynomials, Riesz’s lemma 469 A.12. The Enestrem-Kakey theorem about zeros of polynomials 470 A.13. Sobolev spaces 471 A.14. Moduli of continuity 471 A.15. Approximation by trigonometric polynomials 472 A.16. Multidimensional Fejer means 473 A.17. Self-similar sets 474 A.18. Difference equations 475 A.19. Landau-Kolmogorov inequality 478 A.20. Legendre polynomials 478 Appendix B. Historical Comments 481 Bibliography 493 Index 505
Preface
Wavelet theory lies at the intersection of pure mathematics and computational mathematics, as well as audio and graphic signal processing and compression and transmission of information. The English word wavelet is a translation of the French “ondelette” originally introduced by A. Grossman and J. Morlet. Under the wavelet system is usually understood dilations and shifts of a single function that form a system of represen- tation in some sense (for example, orthogonal basis in L2(R)). In some situations the wavelet systems consist of shifts and dilations of several functions or an entire sequence. In our monograph the notion of “wavelet” as such is not introduced; a specific meaning is given to such phrases as “wavelet function”, “wavelet space”, “wavelet expansion”, etc. Interest in the study of wavelet systems emerged long before the appearance of the terminology and the laying of the foundation of the theory and was primarily attributable to the need of using them for signal process- ing. In connection with these tasks wavelet analysis was formed (in some sense as an alternative to classical Fourier analysis) in the late 1980s–early 1990s in the works of S. Mallat, Y. Meyer, P. J. Lemarie, I. Daubechies, A. Cohen, R. De- Vore, W. Lawton, C. K. Chui, and others. Wavelet bases have several advantages compared to other bases which are used as tools of approximation. They have the so-called time-frequency localization; i.e., these basis functions as well as their Fourier transforms rapidly decrease at infinity. Due to this property, when we ex- pand in such bases signals whose frequency characteristics vary over time and space (such as speech, music, and seismic signals as well as images) many coefficients of harmonics that are not essential for a space or time region turn out to be small and can be neglected, which leads to a data compression. Permissibility of this deletion is explained by another important property: wavelet expansions are uncondition- ally convergent series. In addition, there are efficient algorithms that allow the fast calculation of coefficients of wavelet expansions. All this attracts numerous special- ists in various fields of applied and engineering mathematics to the use of wavelets. On the other hand, wavelet systems have proved useful for solving some problems of approximation theory and functional analysis. So, the wavelets provide a rare example of where the theory and its practical implementation develop in parallel. The impact on the development of mathematical wavelet theory was made by basic works of Y. Meyer and S. Mallat that introduced the notion of multiresolu- tion analysis, described a method of its construction based on a given (suitable) function, and found explicit formulas for finding an appropriate wavelet function whose shifts and dilations form an orthonormal basis. Due to this theory many ex- amples of wavelet systems have been found whose basic functions are smooth and
ix xPREFACE have good time-frequency localization, in particular, smooth wavelets with compact support. Just such examples were required for applications. In the fifteen-year pe- riod thousands of papers have been written on the development of wavelet theory. Major monographs include books by Y. Meyer [5], I. Daubechies [2], C. K. Chui [6], P. Wojtaszczyk [8], and E. Hernandez and G. A. Weiss [9]. In the Russian literature there are translations of the monographs [2]and[6], a textbook by A. P. Petukhov [10], chapters in monographs by B. S. Kashin and A. A. Sahakian [1], V. I. Berdy- shevandL.V.Petrak[11], as well as surveys by I. Ya. Novikov and S. B. Stechkin [43], [44] and N. M. Astaf eva [45]. The above list is not exhaustive; in particular, we are not citing books dedicated to narrow special issues and books in the engi- neering field. The book which we offer to the reader is the first monograph in the Russian literature which is devoted entirely to a systematic exposition of modern wavelet theory. It details the construction of orthogonal and biorthogonal systems of wavelets and it studies their structural and approximation properties, begin- ning with basic theory and ending with special issues and problems. We present some largely theoretical applications of wavelets. In the first two chapters there are the basic facts of the theory for the one-dimensional and multidimensional cases, respectively. Their presentation, however, does not duplicate any of the above- mentioned books. Many of the known fundamental assertions are represented in the most general form or have new proofs. The majority of the material presented in subsequent chapters was not given in earlier monographs. In particular, for the first time we provide a general theory of periodic multiresolution analysis for the multidimensional case with matrix dilation, the theory of nonstationary wavelets, and offer the results of the local smoothness of wavelet functions. The theory of compactly supported wavelets is offered in detail; the relevant refinement equations are investigated; the fractal properties of the wavelets and their relationship to the classical fractal curves are examined. We discuss different ways of measuring the smoothness of wavelets with compact support. In particular, in an explicit way the moduli of continuity of such wavelets are found, as well as orders of their ap- proximation. A separate chapter is devoted to the time-frequency localization of wavelets. A new construction of modified Daubechies wavelets is given, which pre- serves the localization with a growth of their smoothness. Much attention is paid to convergence of wavelet expansions in various senses, as well as to the evaluation of the order of approximation by wavelets in various functional spaces. Note, however, that this monograph cannot claim to be a complete presenta- tion of all aspects of modern wavelet theory. For example, we did not touch upon the subject of continuous wavelet transform, applications of wavelets to differen- tial equations, as well as many practical applications. All the facts presented in the book are provided with complete proofs except for a small number of inserts, printed in small type. Especially detailed are the proofs given in the basic chapters. Auxiliary facts are contained in the appendix also with proofs (with the exception of only those facts that can be found in widely available monographs). Histori- cal commentary is provided for all chapters, and most chapters have exercises for the reader. This book is intended for readers who are familiar with the basics of classical and functional analysis on the level of a standard university course. Much of the material is available to engineers and, perhaps, could attract their interest. In conclusion, we would like to note that the authors are very grateful to PREFACE xi
S. B. Stechkin—one of the first in Russia who has shown interest in wavelet theory and has in various ways contributed to the involvement of all three authors in this subject matter. The authors also express their gratitude to A. P. Petukhov, who read the manuscript fragments and made some helpful observations.
Basic notation N is the set of positive integers. Rd is the d-dimensional Euclidean space, x =(x1,...,xd), y =(y1,...,yd ) are its d elements (vectors), 0 =(0,...,0) ∈ R ,(x, y)=x1y1 + ···+ xdyd, |x| = (x, x). R = R1. Zd is the integer lattice in Rd. Z = Z1. Zd { ∈ Zd ≥ } + = x : xk 0,k=1,...,d . Z Z1 + = +. Td =[0, 1)d is the d-dimensional torus. μ is the Lebesgue measure in Rd. d χe is the characteristic function of a set e ⊂ R ; it takes the value 1 at the points t ∈ e and 0 at all other points.
δlk is the Kronecker delta, which is equal to 1 for l = k;otherwise,itisequalto0. If a ∈ R,then[a]:=max{n ∈ Z : n ≤ a}. span M is the linear span of a set M, i.e., the set of all finite linear combinations of elements from M. supp f is the support of a function f, i.e., the minimal (with respect to inclusion) closed set such that f is equal to zero almost everywhere on the complement of this set. f (k)= f(t)e−2πi(k,t) dt is the k-th Fourier coefficient, k ∈ Zd, of a function Td f ∈ L(Td) with respect to the trigonometric system. f (x)= f(t)e−2πi(x,t) dt is the Fourier transform of a function f from L(Rd); f Rd d denotes also the Fourier transform of a function f from L2(R )orfromthespace of temperate distributions. F and F −1 are the operators taking a function to its direct and inverse Fourier transforms, respectively. L log L(Td)istheclassoffunctionsf ∈ L(Td) such that