Weakly Differentiable Functions Sobolev Spaces and Functions of Bounded Variation
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- Binding: Hardcover
- Publisher: Springer Verlag
- Publish date: 08/01/1989
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1 Preliminaries.- 1.1 Notation.- Inner product of vectors.- Support of a function.- Boundary of a set.- Distance from a point to a set.- Characteristic function of a set.- Multi-indices.- Partial derivative operators.- Function spaces--continuous, Hlder continuous, Hlder continuous derivatives.- 1.2 Measures on Rn.- Lebesgue measurable sets.- Lebesgue measurability of Borel sets.- Suslin sets.- 1.3 Covering Theorems.- Hausdorff maximal principle.- General covering theorem.- Vitali covering theorem.- Covering lemma, with n-balls whose radii vary in Lipschitzian way.- Besicovitch covering lemma.- Besicovitch differentiation theorem.- 1.4 Hausdorff Measure.- Equivalence of Hausdorff and Lebesgue measures.- Hausdorff dimension.- 1.5 Lp-Spaces.- Integration of a function via its distribution function.- Young''s inequality.- Hlder''s and Jensen''s inequality.- 1.6 Regularization.- Lp-spaces and regularization.- 1.7 Distributions.- Functions and measures, as distributions.- Positive distributions.- Distributions determined by their local behavior.- Convolution of distributions.- Differentiation of distributions.- 1.8 Lorentz Spaces.- Non-increasing rearrangement of a function.- Elementary properties of rearranged functions.- Lorentz spaces.- O''Neil''s inequality, for rearranged functions.- Equivalence of Lp-norm and (p, p)-norm.- Hardy''s inequality.- Inclusion relations of Lorentz spaces.- Exercises.- Historical Notes.- 2 Sobolev Spaces and Their Basic Properties.- 2.1 Weak Derivatives.- Sobolev spaces.- Absolute continuity on lines.- Lp-norm of difference quotients.- Truncation of Sobolev functions.- Composition of Sobolev functions.- 2.2 Change of Variables for Sobolev Functions.- Rademacher''s theorem.- Bi-Lipschitzian change of variables.- 2.3 Approximation of Sobolev Functions by Smooth Functions.- Partition of unity.- Smooth functions are dense in Wk,p.- 2.4 Sobolev Inequalities.- Sobolev''s inequality.- 2.5 The Rellich-Kondrachov Compactness Theorem.- Extension domains.- 2.6 Bessel Potentials and Capacity.- Riesz and Bessel kernels.- Bessel potentials.- Bessel capacity.- Basic properties of Bessel capacity.- Capacitability of Suslin sets.- Minimax theorem and alternate formulation of Bessel capacity.- Metric properties of Bessel capacity.- 2.7 The Best Constant in the Sobolev Inequality.- Co-area formula.- Sobolev''s inequality and isoperimetric inequality.- 2.8 Alternate Proofs of the Fundamental Inequalities.- Hardy-Littlewood-Wiener maximal theorem.- Sobolev''s inequality for Riesz potentials.- 2.9 Limiting Cases of the Sobolev Inequality.- The case kp=n by infinite series.- The best constant in the case kp = n.- An L?-bound in the limiting case.- 2.10 Lorentz Spaces, A Slight Improvement.- Young''s inequality in the context of Lorentz spaces.- Sobolev''s inequality in Lorentz spaces.- The limiting case.- Exercises.- Historical Notes.- 3 Pointwise Behavior of Sobolev Functions.- 3.1 Limits of Integral Averages of Sobolev Functions.- Limiting values of integral averages except for capacity null set.- 3.2 Densities of Measures.- 3.3 Lebesgue Points for Sobolev Functions.- Existence of Lebesgue points except for capacity null set.- Approximate continuity.- Fine continuity everywhere except for capacity null set.- 3.4 LP-Derivatives for Sobolev Functions.- Existence of Taylor expansions Lp.- 3.5 Properties of Lp-Derivatives.- The Spaces TktkTk,ptk,p.- The implication of a function being in Tk,pat all points of a closed set.- 3.6 An Lp-Version of the Whitney Extension Theorem.- Existence of a C? function comparable to the.- distance function to a closed set.- The Whitney extension theorem for functions in Tk,p and tk,p.- 3.7 An Observation on Differentiation.- 3.8 Rademacher''s Theorem in the Lp-Context.- A function in Tk,peverywhere implies it is in tk,palmost everywhere.- 3.9 The Implications of Pointwise Differentiability.- Comparison of Lp-derivatives and distributional derivatives.- If u ? tk,p(x)for everyxand if the.- LP-derivatives are in Lpthen u ? Wk,p.- 3.10 A Lusin-Type Approximation for Sobolev Functions.- Integral averages of Sobolev functions are uniformly close to their limits on the complement of sets of small capacity.- Existence of smooth functions that agree with Sobolev functions on the complement of sets of small capacity.- 3.11 The Main Approximation.- Existence of smooth functions that agree with Sobolev functions on the complement of sets of small capacity and are close in norm.- Exercises.- Historical Notes.- 4 Poincar Inequalities--A Unified Approach.- 4.1 Inequalities in a General Setting.- An abstract version of the Poincar inequality.- 4.2 Applications to Sobolev Spaces.- An interpolation inequality.- 4.3 The Dual of WM,p(?).- The representation of (W0M,p(?) )*.- 4.4 Some Measures in (W0M,p(?))*.- Poincar inequalities derived from the abstract version by identifying Lebesgue and Hausdorff measure with elements in (WM,p(?))*.- The trace of Sobolev functions on the boundary of Lipschitz domains.- Poincar inequalities involving the trace of a Sobolev function.- 4.5 Poincar Inequalities.- Inequalities involving the capacity of the set on which a function vanishes.- 4.6 Another Version of Poincar''s Inequality.- An inequality involving dependence on the set on which the function vanishes, not merely on its capacity.- 4.7 More Measures in (WM,p(?))*.- Sobolev''s inequality for Riesz potentials involving measures other than Lebesgue measure.- Characterization of measures in (WM,p(?))*.- 4.8 Other Inequalities Involving Measures in (WM,p)*.- Inequalities involving the restriction of Hausdorff measure to lower dimensional manifolds.- 4.9 The Case p= 1.- Inequalities involving the L1-norm of the gradient.- Exercises.- Historical Notes.- 5 Functions of Bounded Variation.- 5.1 Definitions.- Definition of BV functions.- The total variation measure ? Du'.- 5.2 Elementary Properties of BV Functions.- Lower semicontinuity of the total variation measure.- A condition ensuring continuity of the total variation measure.- 5.3 Regularization of BV Functions.- Regularization does not increase the BV norm.- Approximation of BV functions by smooth functions Compactness in L1of the unit ball in BV.- 5.4 Sets of Finite Perimeter.- Definition of sets of finite perimeter.- The perimeter of domains with smooth boundaries.- Isoperimetric and relative isoperimetric inequality for sets of finite perimeter.- 5.5 The Generalized Exterior Normal.- A preliminary version of the Gauss-Green theorem.- Density results at points of the reduced boundary.- 5.6 Tangential Properties of the Reduced Boundary and the Measure-Theoretic Normal.- Blow-up at a point of the reduced boundary.- The measure-theoretic normal.- The reduced boundary is contained in the measure-theoretic boundary.- A lower bound for the density of ?DXE'.- Hausdorff measure restricted to the reduced boundary is bounded above by ?DXE'.- 5.7 Rectifiability of the Reduced Boundary.- Countably (n -- 1)-rectifiable sets.- Countable (n -- 1)-rectifiability of the measure-theoretic boundary.- 5.8 The Gauss-Green Theorem.- The equivalence of the restriction of Hausdorff measure to the measure-theoretic boundary and ?DXE'.- The Gauss-Green theorem for sets of finite perimeter.- 5.9 Pointwise Behavior of BV Functions.- Upper and lower approximate limits.- The Boxing inequality.- The set of approximate jump discontinuities.- 5.10 The Trace of a BV Function.- The bounded extension of BV functions.- Trace of a BV function defined in terms of the upper and lower approximate limits of the extended function.- The integrability of the trace over the.- measure-theoretic boundary.- 5.11 Sobolev-Type Inequalities for BV Functions.- Inequalities involving elements in (BV(?))*.- 5.12 Inequalities Involving Capacity.- Characterization of measure in (BV(?))*.- Poincar inequality for BV functions.- 5.13 Generalizations to the Case p> 1.- 5.14 Trace Defined in Terms of Integral Averages.- Exercises.- Historical Notes.- List of Symbols.
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