Scale Calculus and M-Polyfold Theory
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Uniform Boundedness Principle for Unbounded Operators
UNIFORM BOUNDEDNESS PRINCIPLE FOR UNBOUNDED OPERATORS C. GANESA MOORTHY and CT. RAMASAMY Abstract. A uniform boundedness principle for unbounded operators is derived. A particular case is: Suppose fTigi2I is a family of linear mappings of a Banach space X into a normed space Y such that fTix : i 2 Ig is bounded for each x 2 X; then there exists a dense subset A of the open unit ball in X such that fTix : i 2 I; x 2 Ag is bounded. A closed graph theorem and a bounded inverse theorem are obtained for families of linear mappings as consequences of this principle. Some applications of this principle are also obtained. 1. Introduction There are many forms for uniform boundedness principle. There is no known evidence for this principle for unbounded operators which generalizes classical uniform boundedness principle for bounded operators. The second section presents a uniform boundedness principle for unbounded operators. An application to derive Hellinger-Toeplitz theorem is also obtained in this section. A JJ J I II closed graph theorem and a bounded inverse theorem are obtained for families of linear mappings in the third section as consequences of this principle. Go back Let us assume the following: Every vector space X is over R or C. An α-seminorm (0 < α ≤ 1) is a mapping p: X ! [0; 1) such that p(x + y) ≤ p(x) + p(y), p(ax) ≤ jajαp(x) for all x; y 2 X Full Screen Close Received November 7, 2013. 2010 Mathematics Subject Classification. Primary 46A32, 47L60. Key words and phrases. -
The Index of Normal Fredholm Elements of C* -Algebras
proceedings of the american mathematical society Volume 113, Number 1, September 1991 THE INDEX OF NORMAL FREDHOLM ELEMENTS OF C*-ALGEBRAS J. A. MINGO AND J. S. SPIELBERG (Communicated by Palle E. T. Jorgensen) Abstract. Examples are given of normal elements of C*-algebras that are invertible modulo an ideal and have nonzero index, in contrast to the case of Fredholm operators on Hubert space. It is shown that this phenomenon occurs only along the lines of these examples. Let T be a bounded operator on a Hubert space. If the range of T is closed and both T and T* have a finite dimensional kernel then T is Fredholm, and the index of T is dim(kerT) - dim(kerT*). If T is normal then kerT = ker T*, so a normal Fredholm operator has index 0. Let us consider a generalization of the notion of Fredholm operator intro- duced by Atiyah. Let X be a compact Hausdorff space and consider continuous functions T: X —>B(H), where B(H) is the set of bounded linear operators on a separable infinite dimensional Hubert space with the norm topology. The set of such functions forms a C*- algebra C(X) <g>B(H). A function T is Fredholm if T(x) is Fredholm for each x . Atiyah [1, Appendix] showed how such an element has an index which is an element of K°(X). Suppose that T is Fredholm and T(x) is normal for each x. Is the index of T necessarily 0? There is a generalization of this question that we would like to consider. -
Bibliography
Bibliography [1] E. Abe, Hopf algebras. Cambridge University Press, 1980. [2] M. Abramowitz and I.A. Stegun, Handbook of mathematical functions. United States Department of Commerce, 1965. [3] M.S. Agranovich, Spectral properties of elliptic pseudodifferential operators on a closed curve. (Russian) Funktsional. Anal. i Prilozhen. 13 (1979), no. 4, 54–56. (English translation in Functional Analysis and Its Applications. 13, p. 279–281.) [4] M.S. Agranovich, Elliptic pseudodifferential operators on a closed curve. (Russian) Trudy Moskov. Mat. Obshch. 47 (1984), 22–67, 246. (English translation in Transactions of Moscow Mathematical Society. 47, p. 23–74.) [5] M.S. Agranovich, Elliptic operators on closed manifolds (in Russian). Itogi Nauki i Tehniki, Ser. Sovrem. Probl. Mat. Fund. Napravl. 63 (1990), 5–129. (English translation in Encyclopaedia Math. Sci. 63 (1994), 1–130.) [6] B.A. Amosov, On the theory of pseudodifferential operators on the circle. (Russian) Uspekhi Mat. Nauk 43 (1988), 169–170; translation in Russian Math. Surveys 43 (1988), 197–198. [7] B.A. Amosov, Approximate solution of elliptic pseudodifferential equations on a smooth closed curve. (Russian) Z. Anal. Anwendungen 9 (1990), 545– 563. [8] P. Antosik, J. Mikusi´nski and R. Sikorski, Theory of distributions. The se- quential approach. Warszawa. PWN – Polish Scientific Publishers, 1973. [9] A. Baker, Matrix Groups. An Introduction to Lie Group Theory. Springer- Verlag, 2002. [10] J. Barros-Neto, An introduction to the theory of distributions . Marcel Dekker, Inc., 1973. [11] R. Beals, Advanced mathematical analysis. Springer-Verlag, 1973. [12] R. Beals, Characterization of pseudodifferential operators and applications. Duke Mathematical Journal. 44 (1977), 45–57. -
Basic Theory of Fredholm Operators Annali Della Scuola Normale Superiore Di Pisa, Classe Di Scienze 3E Série, Tome 21, No 2 (1967), P
ANNALI DELLA SCUOLA NORMALE SUPERIORE DI PISA Classe di Scienze MARTIN SCHECHTER Basic theory of Fredholm operators Annali della Scuola Normale Superiore di Pisa, Classe di Scienze 3e série, tome 21, no 2 (1967), p. 261-280 <http://www.numdam.org/item?id=ASNSP_1967_3_21_2_261_0> © Scuola Normale Superiore, Pisa, 1967, tous droits réservés. L’accès aux archives de la revue « Annali della Scuola Normale Superiore di Pisa, Classe di Scienze » (http://www.sns.it/it/edizioni/riviste/annaliscienze/) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/conditions). Toute utilisa- tion commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ BASIC THEORY OF FREDHOLM OPERATORS (*) MARTIN SOHECHTER 1. Introduction. " A linear operator A from a Banach space X to a Banach space Y is called a Fredholm operator if 1. A is closed 2. the domain D (A) of A is dense in X 3. a (A), the dimension of the null space N (A) of A, is finite 4. .R (A), the range of A, is closed in Y 5. ~ (A), the codimension of R (A) in Y, is finite. The terminology stems from the classical Fredholm theory of integral equations. Special types of Fredholm operators were considered by many authors since that time, but systematic treatments were not given until the work of Atkinson [1]~ Gohberg [2, 3, 4] and Yood [5]. These papers conside- red bounded operators. -
Homework 3 1. If the Inverse T−1 of a Closed Linear Operator Exists, Show
Homework 3 1. If the inverse T −1 of a closed linear operator exists, show that T −1 is a closed linear operator. Solution: Assuming that the inverse of T were defined, then we will have to have that −1 −1 D(T ) = Ran(T ). Suppose that fung 2 D(T ) is a sequence such that un ! u and −1 −1 −1 T un ! x. We need so that that u 2 D(T ) and T u = x. Then by the simple criteria, we would have that T −1 is closed. −1 Since un 2 D(T ) we have that un = T xn, where xn 2 D(T ). Also, note we have that −1 T un = xn ! x. So, we have a sequence of vectors fxng 2 D(T ) with xn ! x and T xn ! u. Since T is closed, we have that x 2 D(T ) and T x = u. But, this last equality implies that u 2 D(T −1) and that x = T −1u, which is what we wanted. 2. Let T be a closed linear operator. If two sequences fxng and fx~ng in the domain of T both converge to the same limit x, and if fT xng and fT x~ng both converge, show that fT xng and fT x~ng both have the same limit. Solution: Suppose that fxng; fx~ng 2 D(T ) are such that xn ! x andx ~n ! x. Let T xn ! y and T x~n ! y~. We need to show that y =y ~. Since T is closed, then we know that for xn ! x and T xn ! y implies that x 2 D(T ) and T x = y. -
1. Introduction
A STRONG OPEN MAPPING THEOREM FOR SURJECTIONS FROM CONES ONTO BANACH SPACES MARCEL DE JEU AND MIEK MESSERSCHMIDT Abstract. We show that a continuous additive positively homogeneous map from a closed not necessarily proper cone in a Banach space onto a Banach space is an open map precisely when it is surjective. This generalization of the usual Open Mapping Theorem for Banach spaces is then combined with Michael's Selection Theorem to yield the existence of a continuous bounded positively homogeneous right inverse of such a surjective map; a strong version of the usual Open Mapping Theorem is then a special case. As another conse- quence, an improved version of the analogue of Andô's Theorem for an ordered Banach space is obtained for a Banach space that is, more generally than in Andô's Theorem, a sum of possibly uncountably many closed not necessarily proper cones. Applications are given for a (pre)-ordered Banach space and for various spaces of continuous functions taking values in such a Banach space or, more generally, taking values in an arbitrary Banach space that is a nite sum of closed not necessarily proper cones. 1. Introduction Consider the following question, that arose in other research of the authors: Let X be a real Banach space, ordered by a closed generating proper cone X+, and let Ω be a topological space. Then the Banach space C0(Ω;X), consisting of the continuous X-valued functions on Ω vanishing at innity, is ordered by the natural + closed proper cone C0(Ω;X ). Is this cone also generating? If X is a Banach + − lattice, then the answer is armative. -
Notex on Fredholm (And Compact) Operators
Notex on Fredholm (and compact) operators October 5, 2009 Abstract In these separate notes, we give an exposition on Fredholm operators between Banach spaces. In particular, we prove the theorems stated in the last section of the first lecture 1. Contents 1 Fredholm operators: basic properties 2 2 Compact operators: basic properties 3 3 Compact operators: the Fredholm alternative 4 4 The relation between Fredholm and compact operators 7 1emphasize that some of the extra-material is just for your curiosity and is not needed for the promised proofs. It is a good exercise for you to cross out the parts which are not needed 1 1 Fredholm operators: basic properties Let E and F be two Banach spaces. We denote by L(E, F) the space of bounded linear operators from E to F. Definition 1.1 A bounded operator T : E −→ F is called Fredholm if Ker(A) and Coker(A) are finite dimensional. We denote by F(E, F) the space of all Fredholm operators from E to F. The index of a Fredholm operator A is defined by Index(A) := dim(Ker(A)) − dim(Coker(A)). Note that a consequence of the Fredholmness is the fact that R(A) = Im(A) is closed. Here are the first properties of Fredholm operators. Theorem 1.2 Let E, F, G be Banach spaces. (i) If B : E −→ F and A : F −→ G are bounded, and two out of the three operators A, B and AB are Fredholm, then so is the third, and Index(A ◦ B) = Index(A) + Index(B). -
Fredholm Operators and Spectral Flow, Canad
Fredholm Operators and Spectral Flow Nils Waterstraat arXiv:1603.02009v1 [math.FA] 7 Mar 2016 2 Contents 1 Linear Operators 7 1.1 BoundedOperatorsandSubspaces . ...... 7 1.2 ClosedOperators................................. ... 10 1.3 SpectralTheory.................................. ... 15 2 Selfadjoint Operators 21 2.1 DefinitionsandBasicProperties . ....... 21 2.2 Spectral Theoryof Selfadjoint Operators . ........... 26 3 The Gap Topology 29 3.1 DefinitionandProperties . ..... 29 3.2 StabilityofSpectra.............................. ..... 34 3.3 Spaces ofSelfadjoint FredholmOperators . .......... 36 4 The Spectral Flow 39 4.1 DefinitionoftheSpectralFlow . ...... 39 4.2 PropertiesandUniqueness. ...... 42 4.3 CrossingForms ................................... .. 46 5 A Simple Example and a Glimpse at the Literature 49 5.1 ASimpleExample .................................. 49 5.2 AGlimpseattheLiterature. ..... 51 3 4 CONTENTS Introduction Fredholm operators are one of the most important classes of linear operators in mathematics. They were introduced around 1900 in the study of integral operators and by definition they share many properties with linear operators between finite dimensional spaces. They appear naturally in global analysis which is a branch of pure mathematics concerned with the global and topological properties of systems of differential equations on manifolds. One of the basic important facts says that every linear elliptic differential operator acting on sections of a vector bundle over a closed manifold induces a Fredholm operator on a suitable Banach space comple- tion of bundle sections. Every Fredholm operator has an integer-valued index, which is invariant under deformations of the operator, and the most fundamental theorem in global analysis is the Atiyah-Singer index theorem [AS68] which gives an explicit formula for the Fredholm index of an elliptic operator on a closed manifold in terms of topological data. -
Fredholm Operators and Atkinson's Theorem
1 A One Lecture Introduction to Fredholm Operators Craig Sinnamon 250380771 December, 2009 1. Introduction This is an elementary introdution to Fredholm operators on a Hilbert space H. Fredholm operators are named after a Swedish mathematician, Ivar Fredholm(1866-1927), who studied integral equations. We will introduce two definitions of a Fredholm operator and prove their equivalance. We will also discuss briefly the index map defined on the set of Fredholm operators. Note that results proved in 4154A Functional Analysis by Prof. Khalkhali may be used without proof. Definition 1.1: A bounded, linear operator T : H ! H is said to be Fredholm if 1) rangeT ⊆ H is closed 2) dimkerT < 1 3) dimketT ∗ < 1 Notice that for a bounded linear operator T on a Hilbert space H, kerT ∗ = (ImageT )?. Indeed: x 2 kerT ∗ , T ∗x = 0 ,< T ∗x; y >= 0 for all y 2 H ,< x:T y >= 0 , x 2 (ImageT )? A good way to think about these Fredholm operators is as operators that are "almost invertible". This notion of "almost invertible" will be made pre- cise later. For now, notice that that operator is almost injective as it has only a finite dimensional kernal, and almost surjective as kerT ∗ = (ImageT )? is also finite dimensional. We will now introduce some algebraic structure on the set of all bounded linear functionals, L(H) and from here make the above discussion precise. 2 2. Bounded Linear Operators as a Banach Algebra Definition 2.1:A C algebra is a ring A with identity along with a ring homomorphism f : C ! A such that 1 7! 1A and f(C) ⊆ Z(A). -
Linear Maps on Hilbert Spaces
Chapter 10 Linear Maps on Hilbert Spaces A special tool called the adjoint helps provide insight into the behavior of linear maps on Hilbert spaces. This chapter begins with a study of the adjoint and its connection to the null space and range of a linear map. Then we discuss various issues connected with the invertibility of operators on Hilbert spaces. These issues lead to the spectrum, which is a set of numbers that gives important information about an operator. This chapter then looks at special classes of operators on Hilbert spaces: self- adjoint operators, normal operators, isometries, unitary operators, integral operators, and compact operators. Even on infinite-dimensional Hilbert spaces, compact operators display many characteristics expected from finite-dimensional linear algebra. We will see that the powerful Spectral Theorem for compact operators greatly resembles the finite- dimensional version. Also, we develop the Singular Value Decomposition for an arbitrary compact operator, again quite similar to the finite-dimensional result. The Botanical Garden at Uppsala University (the oldest university in Sweden, founded in 1477), where Erik Fredholm (1866–1927) was a student. The theorem called the Fredholm Alternative, which we prove in this chapter, states that a compact operator minus a nonzero scalar multiple of the identity operator is injective if and only if it is surjective. CC-BY-SA Per Enström © Sheldon Axler 2020 S. Axler, Measure, Integration & Real Analysis, Graduate Texts 280 in Mathematics 282, https://doi.org/10.1007/978-3-030-33143-6_10 Section 10A Adjoints and Invertibility 281 10A Adjoints and Invertibility Adjoints of Linear Maps on Hilbert Spaces The next definition provides a key tool for studying linear maps on Hilbert spaces. -
A → B Between Banach Spaces Is a Fredholm Operator If Ker L and Coker L Are finite Dimensional
LECTURE 6. PART III, MORSE HOMOLOGY, 2011 HTTP://MORSEHOMOLOGY.WIKISPACES.COM 2.3. Fredholm theory. Def. A bounded linear map L : A → B between Banach spaces is a Fredholm operator if ker L and coker L are finite dimensional. Def. A map f : M → N between Banach mfds is a Fredholm map if dpf : TpM → Tf(p)N is a Fredholm operator. Basic Facts about Fredholm operators (1) K = ker L has a closed complement A0 ⊂ A. (so the implicit function theorem applies to Fredholm maps). 1 ∗ ∗ ∗ ∗ Pf. pick basis v1,...,vk of K, pick dual v1 ,...,vk ∈ A . A0 = ∩ ker vi . (2) im(L)= image(L) ⊂ B is closed. (so coker L = B/im(L) is Banach) Pf. pick complement C to im(L). C is finite dim’l, so closed, so Banach. ⇒ L : A/K ⊕ C → B,L(a,c)= La + c is a bounded linear bijection, hence an iso (open mapping theorem). So L(A/K) = Im(L) is closed. (3) A = A0 ⊕K, B = B0 ⊕C where B0 = im(L), C = complement (=∼ coker L). iso 0 ⇒ L = 0 0 : A0 ⊕ K → B0 ⊕ C Def. index(L) = dim ker L − dim coker L. (4) Perturbing L preserves the Fredholm condition and the index: Claim.2 s : A → B bdd linear with small norm ⇒ ∃ “change of basis” isos i : A ∼ B ⊕ K = 0 such that j ◦ (L + s) ◦ i = I 0 j : B =∼ B0 ⊕ C 0 ℓ for some linear map ℓ : K → C. Note: dim ker drops by rank(ℓ), but also dim coker drops by rank(ℓ). -
Fredholm Operators and the Generalized Index
FREDHOLM OPERATORS AND THE GENERALIZED INDEX JOSEPH BREEN CONTENTS 1. Introduction 1 1.1. Index Theory in Finite Dimensions 2 2. The Space of Fredholm Operators 3 3. Vector Bundles and K-Theory 6 3.1. Vector Bundles 6 3.2. K-Theory 8 4. The Atiyah-Janich¨ Theorem 9 4.1. The Generalized Index Map 10 5. Index Theory Examples 12 5.1. Toeplitz Operators and the Toeplitz Index Theorem 12 5.2. The Atiyah-Singer Index Theorem 14 6. Conclusion 16 References 17 1. INTRODUCTION One of the most fundamental problems in mathematics is to solve linear equations of the form T f = g, where T is a linear transformation, g is known, and f is some unknown quantity. The simplest example of this comes from elementary linear algebra, which deals with solutions to matrix-vector equations of the form Ax = b. More generally, if V; W are vector spaces (or, in particular, Hilbert or Banach spaces), we might be interested in solving equations of the form T v = w where v 2 V , w 2 W , and T is a linear map from V ! W . A more explicit source of examples is that of differential equations. For instance, one can seek solutions to a system of differential equations of the form Ax(t) = x0(t), where, again, A is a matrix. From physics, we get important partial differential equations such as Poisson’s equation: ∆f = g, Pn @2 n where ∆ = i=1 2 and f and g are functions on R . In general, we can take certain partial @xi differential equations and repackage them in the form Df = g for some suitable differential operator D between Banach spaces.