Norm Inequalities for Derivatives and Differences

Norm inequalities relating (i) a function and two of its derivatives and (ii) a sequence and two of its differences are studied. Detailed elementary proofs of basic inequalities are given. These are accessible to anyone with a background of advanced calcu

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1536

Lecture Notes in Mathematics Editors: A. Dold, Heidelberg B. Eckmann, Ziirich F. Takens, Groningen

1536

Man Kam Kwong Anton Zettl

N arm Inequalities for Derivatives and Differences

Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest

Authors Man Kam Kwong Mathematics and Computer Science Division Argonne National Laboratory Argonne, IL 60439 USA Anton Zettl Department of Mathematical Sciences Northern Illinois University DeKalb, IL 60115 USA

Mathematics Subject Classification (1991): 2602, 26D I5, 3902, 39A 12, 39A70, 39B72, 47A30, 47B39

ISBN 3-540-56387-3 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-56387-3 Springer-Verlag New York Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1992 Printed in Germany Typesetting: Camera ready by author Printing and binding: Druckhaus Beltz, Hemsbach/Bergstr. 46/3140-543210 - Printed on acid-free paper

Contents

Introd uction

1

1

3

2

Unit Weight Functions 1.1

The Norms of

y

and

1.2

The Norms of

y, y(k),

1.3

Inequalities of Product Form

12

1.4

Growth at Infinity .

26

1.5

Notes and Problems

29

3

y(n)

and

y(n)

6

The Norms of y, y',v"

35

2.1

Introduction.

35

2.2

The Loo Case

35

2.3

The L2 Case

36

2.4

Equivalent Bounded Interval Problems for R

38

2.5

Equivalent Bounded Interval Problems for R+ .

43

2.6

The L1 Case

...................

45

2.7

Upper and Lower Bounds for k(p, R) and k(p, R+)

47

2.8

Extremals . . . . . . . . . . .

55

2.9

Continuity as a Function of p

77

2.10 Landau's Inequality for Nondifferentiable Functions.

80

VI

3

4

2.11 Notes and Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

81

Weights

84

3.1 Inequalities of the Sum Form

84

3.2 Inequalities of Product Form

95

3.3 Monotone Weight Functions .

97

3.4 Positive Weight Functions

104

3.5 Weights with Zeros .

109

3.6 Notes and Problems

115

The Difference Operator

117

4.1 The Discrete Product Inequality

117

4.2 The Second Order Case

120

4.3 Extremals . . . . . .

123

4.4 Notes and Problems

137

References

144

Subject Index

149

Preface Edmund Landau's 1913 paper "Einige Ungleichungen fiir zweimal differenzierbare Funktionen", based on earlier work of Hardy and Littlewood, initiated a vast and fruitful research activity involving the study of the relationship between the norms of (i) a function and its derivatives and (ii) a sequence and its differences. These