Sufficient Generalities About Topological Vector Spaces

Total Page:16

File Type:pdf, Size:1020Kb

Sufficient Generalities About Topological Vector Spaces (November 28, 2016) Topological vector spaces Paul Garrett [email protected] http:=/www.math.umn.edu/egarrett/ [This document is http://www.math.umn.edu/~garrett/m/fun/notes 2016-17/tvss.pdf] 1. Banach spaces Ck[a; b] 2. Non-Banach limit C1[a; b] of Banach spaces Ck[a; b] 3. Sufficient notion of topological vector space 4. Unique vectorspace topology on Cn 5. Non-Fr´echet colimit C1 of Cn, quasi-completeness 6. Seminorms and locally convex topologies 7. Quasi-completeness theorem 1. Banach spaces Ck[a; b] We give the vector space Ck[a; b] of k-times continuously differentiable functions on an interval [a; b] a metric which makes it complete. Mere pointwise limits of continuous functions easily fail to be continuous. First recall the standard [1.1] Claim: The set Co(K) of complex-valued continuous functions on a compact set K is complete with o the metric jf − gjCo , with the C -norm jfjCo = supx2K jf(x)j. Proof: This is a typical three-epsilon argument. To show that a Cauchy sequence ffig of continuous functions has a pointwise limit which is a continuous function, first argue that fi has a pointwise limit at every x 2 K. Given " > 0, choose N large enough such that jfi − fjj < " for all i; j ≥ N. Then jfi(x) − fj(x)j < " for any x in K. Thus, the sequence of values fi(x) is a Cauchy sequence of complex numbers, so has a limit 0 0 f(x). Further, given " > 0 choose j ≥ N sufficiently large such that jfj(x) − f(x)j < " . For i ≥ N 0 jfi(x) − f(x)j ≤ jfi(x) − fj(x)j + jfj(x) − f(x)j < " + " 0 This is true for every positive " , so jfi(x) − f(x)j ≤ " for every x in K. That is, the pointwise limit is approached uniformly in x 2 [a; b]. To prove that f(x) is continuous, for " > 0, take N be large enough so that jfi − fjj < " for all i; j ≥ N. From the previous paragraph jfi(x) − f(x)j ≤ " for every x and for i ≥ N. Fix i ≥ N and x 2 K, and choose a small enough neigborhood U of x such that jfi(x) − fi(y)j < " for any y in U. Then jf(x) − f(y)j ≤ jf(x) − fi(x)j + jfi(x) − fi(y)j + jf(y) − fi(y)j ≤ " + jfi(x) − fi(y)j + " < " + " + " Thus, the pointwise limit f is continuous at every x in U. === Unsurprisingly, but significantly: [1.2] Claim: For x 2 [a; b], the evaluation map f ! f(x) is a continuous linear functional on Co[a; b]. Proof: For jf − gjCo < ", we have jf(x) − g(x)j ≤ jf − gjCo < " proving the continuity. === 1 Paul Garrett: Topological vector spaces (November 28, 2016) As usual, a real-valued or complex-valued function f on a closed interval [a; b] ⊂ R is continuously differentiable when it has a derivative which is itself a continuous function. That is, the limit f(x + h) − f(x) f 0(x) = lim h!0 h exists for all x 2 [a; b], and the function f 0(x) is in Co[a; b]. Let Ck[a; b] be the collection of k-times continuously differentiable functions on [a; b], with the Ck-norm X (i) X (i) jfjCk = sup jf (x)j = jf j1 0≤i≤k x2[a;b] 0≤i≤k (i) th k where f is the i derivative of f. The associated metric on C [a; b] is jf − gjCk . Similar to the assertion about evaluation on Co[a; b], [1.3] Claim: For x 2 [a; b] and 0 ≤ j ≤ k, the evaluation map f ! f (j)(x) is a continuous linear functional on Ck[a; b]. Proof: For jf − gjCk < ", (j) (j) jf (x) − g (x)j ≤ jf − gjCk < " proving the continuity. === We see that Ck[a; b] is a Banach space: [1.4] Theorem: The normed metric space Ck[a; b] is complete. k (j) Proof: For a Cauchy sequence ffig in C [a; b], all the pointwise limits limi fi (x) of j-fold derivatives exist (j) for 0 ≤ j ≤ k, and are uniformly continuous. The issue is to show that limi f is differentiable, with (j+1) 1 derivative limi f . It suffices to show that, for a Cauchy sequence fn in C [a; b], with pointwise limits 0 0 f(x) = limn fn(x) and g(x) = limn fn(x) we have g = f . By the fundamental theorem of calculus, for any index i, Z x 0 fi(x) − fi(a) = fi (t) dt a 0 0 Since the fi uniformly approach g, given " > 0 there is io such that jfi (t) − g(t)j < " for i ≥ io and for all t in the interval, so for such i Z x Z x Z x 0 0 fi (t) dt − g(t) dt ≤ jfi (t) − g(t)j dt ≤ " · jx − aj −! 0 a a a Thus, Z x Z x 0 lim fi(x) − fi(a) = lim fi (t) dt = g(t) dt i i a a from which f 0 = g. === By design, we have d k k−1 [1.5] Theorem: The map dx : C [a; b] ! C [a; b] is continuous. Proof: As usual, for a linear map T : V ! W , by linearity T v − T v0 = T (v − v0) it suffices to check continuity at 0. For Banach spaces the homogeneity jσ · vjV = jαj · jvjV shows that continuity is equivalent to existence of a constant B such that jT vjW ≤ B · jvjV for v 2 V . Then d X df (i) X (i) j fj k−1 = sup j( ) (x)j = sup jf (x)j ≤ 1 · jfj k dx C dx C 0≤i≤k−1 x2[a;b] 1≤i≤k x2[a;b] 2 Paul Garrett: Topological vector spaces (November 28, 2016) as desired. === 2. Non-Banach limit C1[a; b] of Banach spaces Ck[a; b] The space C1[a; b] of infinitely differentiable complex-valued functions on a (finite) interval [a; b] in R is not a Banach space. [1] Nevertheless, the topology is completely determined by its relation to the Banach spaces Ck[a; b]. That is, there is a unique reasonable topology on C1[a; b]. After explaining and proving this uniqueness, we also show that this topology is complete metric. This function space can be presented as \ C1[a; b] = Ck[a; b] k≥0 and we reasonably require that whatever topology C1[a; b] should have, each inclusion C1[a; b] −! Ck[a; b] is continuous. At the same time, given a family of continuous linear maps Z ! Ck[a; b] from a vector space Z in some reasonable class (specified in the next section), with the compatibility condition of giving commutative diagrams ⊂ Ck[a; b] / Ck−1[a; b] fMM O MMM MMM MMM Z the image of Z actually lies in the intersection C1[a; b]. Thus, diagrammatically, for every family of compatible maps Z ! Ck[a; b], there is a unique Z ! C1[a; b] fitting into a commutative diagram * ( C1[a; b] ::: / C1[a; b] / Co[a; b] c w; j j4 w 8 j j 9! w j j w j j Z jw j We require that this induced map Z ! C1[a; b] is continuous. When we know that these conditions are met, we would say that C1[a; b] is the (projective) limit of the spaces Ck[a; b], written C1[a; b] = lim Ck[a; b] k with implicit reference to the inclusions Ck+1[a; b] ! Ck[a; b] and C1[a; b] ! Ck[a; b]. [2.1] Claim: Up to unique isomorphism, there exists at most one topology on C1[a; b] such that to every compatible family of continuous linear maps Z ! Ck[a; b] from a topological vector space Z there is a unique continuous linear Z ! C1[a; b] fitting into a commutative diagram as just above. Proof: Let X; Y be C1[a; b] with two topologies fitting into such diagrams, and show X ≈ Y , and for a unique isomorphism. First, claim that the identity map idX : X ! X is the only map ' : X ! X fitting into a commutative diagram [1] It is not essential to prove that there is no reasonable Banach space structure on C1[a; b], but this can be readily proven in a suitable context. 3 Paul Garrett: Topological vector spaces (November 28, 2016) * ' X ::: / C1[a; b] / Co[a; b] O ' X ::: / C1[a; b] / Co[a; b] 4 7 Indeed, given a compatible family of maps X ! Ck[a; b], there is unique ' fitting into * ' X ::: / C1[a; b] / Co[a; b] ` w; j j4 w 8 j j ' w j j w j j X jw j Since the identity map idX fits, necessarily ' = idX . Similarly, given the compatible family of inclusions Y ! Ck[a; b], there is unique f : Y ! X fitting into * ' X ::: / C1[a; b] / Co[a; b] ` ; j4 ww jjjj ww jjjj f ww jjj ww jjjj Y jwjj Similarly, given the compatible family of inclusions X ! Ck[a; b], there is unique g : X ! Y fitting into * ' Y ::: / C1[a; b] / Co[a; b] _ ; j4 ww jjj ww jjjj g ww jjjj ww jjjj X jwjj Then f ◦ g : X ! X fits into a diagram * ' X ::: / C1[a; b] / Co[a; b] ` ; j4 ww jjjj ww jjjj f◦g ww jjj ww jjjj X jwjj Therefore, f ◦ g = idX .
Recommended publications
  • Completeness in Quasi-Pseudometric Spaces—A Survey
    mathematics Article Completeness in Quasi-Pseudometric Spaces—A Survey ¸StefanCobzas Faculty of Mathematics and Computer Science, Babe¸s-BolyaiUniversity, 400 084 Cluj-Napoca, Romania; [email protected] Received:17 June 2020; Accepted: 24 July 2020; Published: 3 August 2020 Abstract: The aim of this paper is to discuss the relations between various notions of sequential completeness and the corresponding notions of completeness by nets or by filters in the setting of quasi-metric spaces. We propose a new definition of right K-Cauchy net in a quasi-metric space for which the corresponding completeness is equivalent to the sequential completeness. In this way we complete some results of R. A. Stoltenberg, Proc. London Math. Soc. 17 (1967), 226–240, and V. Gregori and J. Ferrer, Proc. Lond. Math. Soc., III Ser., 49 (1984), 36. A discussion on nets defined over ordered or pre-ordered directed sets is also included. Keywords: metric space; quasi-metric space; uniform space; quasi-uniform space; Cauchy sequence; Cauchy net; Cauchy filter; completeness MSC: 54E15; 54E25; 54E50; 46S99 1. Introduction It is well known that completeness is an essential tool in the study of metric spaces, particularly for fixed points results in such spaces. The study of completeness in quasi-metric spaces is considerably more involved, due to the lack of symmetry of the distance—there are several notions of completeness all agreing with the usual one in the metric case (see [1] or [2]). Again these notions are essential in proving fixed point results in quasi-metric spaces as it is shown by some papers on this topic as, for instance, [3–6] (see also the book [7]).
    [Show full text]
  • On Quasi Norm Attaining Operators Between Banach Spaces
    ON QUASI NORM ATTAINING OPERATORS BETWEEN BANACH SPACES GEUNSU CHOI, YUN SUNG CHOI, MINGU JUNG, AND MIGUEL MART´IN Abstract. We provide a characterization of the Radon-Nikod´ymproperty in terms of the denseness of bounded linear operators which attain their norm in a weak sense, which complement the one given by Bourgain and Huff in the 1970's. To this end, we introduce the following notion: an operator T : X ÝÑ Y between the Banach spaces X and Y is quasi norm attaining if there is a sequence pxnq of norm one elements in X such that pT xnq converges to some u P Y with }u}“}T }. Norm attaining operators in the usual (or strong) sense (i.e. operators for which there is a point in the unit ball where the norm of its image equals the norm of the operator) and also compact operators satisfy this definition. We prove that strong Radon-Nikod´ymoperators can be approximated by quasi norm attaining operators, a result which does not hold for norm attaining operators in the strong sense. This shows that this new notion of quasi norm attainment allows to characterize the Radon-Nikod´ymproperty in terms of denseness of quasi norm attaining operators for both domain and range spaces, completing thus a characterization by Bourgain and Huff in terms of norm attaining operators which is only valid for domain spaces and it is actually false for range spaces (due to a celebrated example by Gowers of 1990). A number of other related results are also included in the paper: we give some positive results on the denseness of norm attaining Lipschitz maps, norm attaining multilinear maps and norm attaining polynomials, characterize both finite dimensionality and reflexivity in terms of quasi norm attaining operators, discuss conditions to obtain that quasi norm attaining operators are actually norm attaining, study the relationship with the norm attainment of the adjoint operator and, finally, present some stability results.
    [Show full text]
  • 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.
    [Show full text]
  • Topological Vector Spaces and Algebras
    Joseph Muscat 2015 1 Topological Vector Spaces and Algebras [email protected] 1 June 2016 1 Topological Vector Spaces over R or C Recall that a topological vector space is a vector space with a T0 topology such that addition and the field action are continuous. When the field is F := R or C, the field action is called scalar multiplication. Examples: A N • R , such as sequences R , with pointwise convergence. p • Sequence spaces ℓ (real or complex) with topology generated by Br = (a ): p a p < r , where p> 0. { n n | n| } p p p p • LebesgueP spaces L (A) with Br = f : A F, measurable, f < r (p> 0). { → | | } R p • Products and quotients by closed subspaces are again topological vector spaces. If π : Y X are linear maps, then the vector space Y with the ini- i → i tial topology is a topological vector space, which is T0 when the πi are collectively 1-1. The set of (continuous linear) morphisms is denoted by B(X, Y ). The mor- phisms B(X, F) are called ‘functionals’. +, , Finitely- Locally Bounded First ∗ → Generated Separable countable Top. Vec. Spaces ///// Lp 0 <p< 1 ℓp[0, 1] (ℓp)N (ℓp)R p ∞ N n R 2 Locally Convex ///// L p > 1 L R , C(R ) R pointwise, ℓweak Inner Product ///// L2 ℓ2[0, 1] ///// ///// Locally Compact Rn ///// ///// ///// ///// 1. A set is balanced when λ 6 1 λA A. | | ⇒ ⊆ (a) The image and pre-image of balanced sets are balanced. ◦ (b) The closure and interior are again balanced (if A 0; since λA = (λA)◦ A◦); as are the union, intersection, sum,∈ scaling, T and prod- uct A ⊆B of balanced sets.
    [Show full text]
  • 171 Composition Operator on the Space of Functions
    Acta Math. Univ. Comenianae 171 Vol. LXXXI, 2 (2012), pp. 171{183 COMPOSITION OPERATOR ON THE SPACE OF FUNCTIONS TRIEBEL-LIZORKIN AND BOUNDED VARIATION TYPE M. MOUSSAI Abstract. For a Borel-measurable function f : R ! R satisfying f(0) = 0 and Z sup t−1 sup jf 0(x + h) − f 0(x)jp dx < +1; (0 < p < +1); t>0 R jh|≤t s n we study the composition operator Tf (g) := f◦g on Triebel-Lizorkin spaces Fp;q(R ) in the case 0 < s < 1 + (1=p). 1. Introduction and the main result The study of the composition operator Tf : g ! f ◦ g associated to a Borel- s n measurable function f : R ! R on Triebel-Lizorkin spaces Fp;q(R ), consists in finding a characterization of the functions f such that s n s n (1.1) Tf (Fp;q(R )) ⊆ Fp;q(R ): The investigation to establish (1.1) was improved by several works, for example the papers of Adams and Frazier [1,2 ], Brezis and Mironescu [6], Maz'ya and Shaposnikova [9], Runst and Sickel [12] and [10]. There were obtained some necessary conditions on f; from which we recall the following results. For s > 0, 1 < p < +1 and 1 ≤ q ≤ +1 n s n s n • if Tf takes L1(R ) \ Fp;q(R ) to Fp;q(R ), then f is locally Lipschitz con- tinuous. n s n • if Tf takes the Schwartz space S(R ) to Fp;q(R ), then f belongs locally to s Fp;q(R). The first assertion is proved in [3, Theorem 3.1].
    [Show full text]
  • View of This, the Following Observation Should Be of Some Interest to Vector Space Pathologists
    Can. J. Math., Vol. XXV, No. 3, 1973, pp. 511-524 INCLUSION THEOREMS FOR Z-SPACES G. BENNETT AND N. J. KALTON 1. Notation and preliminary ideas. A sequence space is a vector subspace of the space co of all real (or complex) sequences. A sequence space E with a locally convex topology r is called a K- space if the inclusion map E —* co is continuous, when co is endowed with the product topology (co = II^Li (R)*). A i£-space E with a Frechet (i.e., complete, metrizable and locally convex) topology is called an FK-space; if the topology is a Banach topology, then E is called a BK-space. The following familiar BK-spaces will be important in the sequel: ni, the space of all bounded sequences; c, the space of all convergent sequences; Co, the space of all null sequences; lp, 1 ^ p < °°, the space of all absolutely ^-summable sequences. We shall also consider the space <j> of all finite sequences and the linear span, Wo, of all sequences of zeros and ones; these provide examples of spaces having no FK-topology. A sequence space is solid (respectively monotone) provided that xy £ E whenever x 6 m (respectively m0) and y £ E. For x £ co, we denote by Pn(x) the sequence (xi, x2, . xn, 0, . .) ; if a i£-space (E, r) has the property that Pn(x) —» x in r for each x G E, then we say that (£, r) is an AK-space. We also write WE = \x Ç £: P„.(x) —>x weakly} and ^ = jx Ç E: Pn{x) —>x in r}.
    [Show full text]
  • Functional Analysis Lecture Notes Chapter 3. Banach
    FUNCTIONAL ANALYSIS LECTURE NOTES CHAPTER 3. BANACH SPACES CHRISTOPHER HEIL 1. Elementary Properties and Examples Notation 1.1. Throughout, F will denote either the real line R or the complex plane C. All vector spaces are assumed to be over the field F. Definition 1.2. Let X be a vector space over the field F. Then a semi-norm on X is a function k · k: X ! R such that (a) kxk ≥ 0 for all x 2 X, (b) kαxk = jαj kxk for all x 2 X and α 2 F, (c) Triangle Inequality: kx + yk ≤ kxk + kyk for all x, y 2 X. A norm on X is a semi-norm which also satisfies: (d) kxk = 0 =) x = 0. A vector space X together with a norm k · k is called a normed linear space, a normed vector space, or simply a normed space. Definition 1.3. Let I be a finite or countable index set (for example, I = f1; : : : ; Ng if finite, or I = N or Z if infinite). Let w : I ! [0; 1). Given a sequence of scalars x = (xi)i2I , set 1=p jx jp w(i)p ; 0 < p < 1; 8 i kxkp;w = > Xi2I <> sup jxij w(i); p = 1; i2I > where these quantities could be infinite.:> Then we set p `w(I) = x = (xi)i2I : kxkp < 1 : n o p p p We call `w(I) a weighted ` space, and often denote it just by `w (especially if I = N). If p p w(i) = 1 for all i, then we simply call this space ` (I) or ` and write k · kp instead of k · kp;w.
    [Show full text]
  • Bornologically Isomorphic Representations of Tensor Distributions
    Bornologically isomorphic representations of distributions on manifolds E. Nigsch Thursday 15th November, 2018 Abstract Distributional tensor fields can be regarded as multilinear mappings with distributional values or as (classical) tensor fields with distribu- tional coefficients. We show that the corresponding isomorphisms hold also in the bornological setting. 1 Introduction ′ ′ ′r s ′ Let D (M) := Γc(M, Vol(M)) and Ds (M) := Γc(M, Tr(M) ⊗ Vol(M)) be the strong duals of the space of compactly supported sections of the volume s bundle Vol(M) and of its tensor product with the tensor bundle Tr(M) over a manifold; these are the spaces of scalar and tensor distributions on M as defined in [?, ?]. A property of the space of tensor distributions which is fundamental in distributional geometry is given by the C∞(M)-module isomorphisms ′r ∼ s ′ ∼ r ′ Ds (M) = LC∞(M)(Tr (M), D (M)) = Ts (M) ⊗C∞(M) D (M) (1) (cf. [?, Theorem 3.1.12 and Corollary 3.1.15]) where C∞(M) is the space of smooth functions on M. In[?] a space of Colombeau-type nonlinear generalized tensor fields was constructed. This involved handling smooth functions (in the sense of convenient calculus as developed in [?]) in par- arXiv:1105.1642v1 [math.FA] 9 May 2011 ∞ r ′ ticular on the C (M)-module tensor products Ts (M) ⊗C∞(M) D (M) and Γ(E) ⊗C∞(M) Γ(F ), where Γ(E) denotes the space of smooth sections of a vector bundle E over M. In[?], however, only minor attention was paid to questions of topology on these tensor products.
    [Show full text]
  • The Nonstandard Theory of Topological Vector Spaces
    TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 172, October 1972 THE NONSTANDARDTHEORY OF TOPOLOGICAL VECTOR SPACES BY C. WARD HENSON AND L. C. MOORE, JR. ABSTRACT. In this paper the nonstandard theory of topological vector spaces is developed, with three main objectives: (1) creation of the basic nonstandard concepts and tools; (2) use of these tools to give nonstandard treatments of some major standard theorems ; (3) construction of the nonstandard hull of an arbitrary topological vector space, and the beginning of the study of the class of spaces which tesults. Introduction. Let Ml be a set theoretical structure and let *JR be an enlarge- ment of M. Let (E, 0) be a topological vector space in M. §§1 and 2 of this paper are devoted to the elementary nonstandard theory of (F, 0). In particular, in §1 the concept of 0-finiteness for elements of *E is introduced and the nonstandard hull of (E, 0) (relative to *3R) is defined. §2 introduces the concept of 0-bounded- ness for elements of *E. In §5 the elementary nonstandard theory of locally convex spaces is developed by investigating the mapping in *JK which corresponds to a given pairing. In §§6 and 7 we make use of this theory by providing nonstandard treatments of two aspects of the existing standard theory. In §6, Luxemburg's characterization of the pre-nearstandard elements of *E for a normed space (E, p) is extended to Hausdorff locally convex spaces (E, 8). This characterization is used to prove the theorem of Grothendieck which gives a criterion for the completeness of a Hausdorff locally convex space.
    [Show full text]
  • On Domain of Nörlund Matrix
    mathematics Article On Domain of Nörlund Matrix Kuddusi Kayaduman 1,* and Fevzi Ya¸sar 2 1 Faculty of Arts and Sciences, Department of Mathematics, Gaziantep University, Gaziantep 27310, Turkey 2 ¸SehitlerMah. Cambazlar Sok. No:9, Kilis 79000, Turkey; [email protected] * Correspondence: [email protected] Received: 24 October 2018; Accepted: 16 November 2018; Published: 20 November 2018 Abstract: In 1978, the domain of the Nörlund matrix on the classical sequence spaces lp and l¥ was introduced by Wang, where 1 ≤ p < ¥. Tu˘gand Ba¸sarstudied the matrix domain of Nörlund mean on the sequence spaces f 0 and f in 2016. Additionally, Tu˘gdefined and investigated a new sequence space as the domain of the Nörlund matrix on the space of bounded variation sequences in 2017. In this article, we defined new space bs(Nt) and cs(Nt) and examined the domain of the Nörlund mean on the bs and cs, which are bounded and convergent series, respectively. We also examined their inclusion relations. We defined the norms over them and investigated whether these new spaces provide conditions of Banach space. Finally, we determined their a-, b-, g-duals, and characterized their matrix transformations on this space and into this space. Keywords: nörlund mean; nörlund transforms; difference matrix; a-, b-, g-duals; matrix transformations 1. Introduction 1.1. Background In the studies on the sequence space, creating a new sequence space and research on its properties have been important. Some researchers examined the algebraic properties of the sequence space while others investigated its place among other known spaces and its duals, and characterized the matrix transformations on this space.
    [Show full text]
  • Comparative Programming Languages
    CSc 372 Comparative Programming Languages 10 : Haskell — Curried Functions Department of Computer Science University of Arizona [email protected] Copyright c 2013 Christian Collberg 1/22 Infix Functions Declaring Infix Functions Sometimes it is more natural to use an infix notation for a function application, rather than the normal prefix one: 5+6 (infix) (+) 5 6 (prefix) Haskell predeclares some infix operators in the standard prelude, such as those for arithmetic. For each operator we need to specify its precedence and associativity. The higher precedence of an operator, the stronger it binds (attracts) its arguments: hence: 3 + 5*4 ≡ 3 + (5*4) 3 + 5*4 6≡ (3 + 5) * 4 3/22 Declaring Infix Functions. The associativity of an operator describes how it binds when combined with operators of equal precedence. So, is 5-3+9 ≡ (5-3)+9 = 11 OR 5-3+9 ≡ 5-(3+9) = -7 The answer is that + and - associate to the left, i.e. parentheses are inserted from the left. Some operators are right associative: 5^3^2 ≡ 5^(3^2) Some operators have free (or no) associativity. Combining operators with free associativity is an error: 5==4<3 ⇒ ERROR 4/22 Declaring Infix Functions. The syntax for declaring operators: infixr prec oper -- right assoc. infixl prec oper -- left assoc. infix prec oper -- free assoc. From the standard prelude: infixl 7 * infix 7 /, ‘div‘, ‘rem‘, ‘mod‘ infix 4 ==, /=, <, <=, >=, > An infix function can be used in a prefix function application, by including it in parenthesis. Example: ? (+) 5 ((*) 6 4) 29 5/22 Multi-Argument Functions Multi-Argument Functions Haskell only supports one-argument functions.
    [Show full text]
  • "Mathematics for Computer Science" (MCS)
    “mcs” — 2016/9/28 — 23:07 — page i — #1 Mathematics for Computer Science revised Wednesday 28th September, 2016, 23:07 Eric Lehman Google Inc. F Thomson Leighton Department of Mathematics and the Computer Science and AI Laboratory, Massachussetts Institute of Technology; Akamai Technologies Albert R Meyer Department of Electrical Engineering and Computer Science and the Computer Science and AI Laboratory, Massachussetts Institute of Technology 2016, Eric Lehman, F Tom Leighton, Albert R Meyer. This work is available under the terms of the Creative Commons Attribution-ShareAlike 3.0 license. “mcs” — 2016/9/28 — 23:07 — page ii — #2 “mcs” — 2016/9/28 — 23:07 — page iii — #3 Contents I Proofs Introduction 3 0.1 References4 1 What is a Proof? 5 1.1 Propositions5 1.2 Predicates8 1.3 The Axiomatic Method8 1.4 Our Axioms9 1.5 Proving an Implication 11 1.6 Proving an “If and Only If” 13 1.7 Proof by Cases 15 1.8 Proof by Contradiction 16 1.9 Good Proofs in Practice 17 1.10 References 19 2 The Well Ordering Principle 29 2.1 Well Ordering Proofs 29 2.2 Template for Well Ordering Proofs 30 2.3 Factoring into Primes 32 2.4 Well Ordered Sets 33 3 Logical Formulas 47 3.1 Propositions from Propositions 48 3.2 Propositional Logic in Computer Programs 51 3.3 Equivalence and Validity 54 3.4 The Algebra of Propositions 56 3.5 The SAT Problem 61 3.6 Predicate Formulas 62 3.7 References 67 4 Mathematical Data Types 93 4.1 Sets 93 4.2 Sequences 98 4.3 Functions 99 4.4 Binary Relations 101 4.5 Finite Cardinality 105 “mcs” — 2016/9/28 — 23:07 — page iv — #4 Contentsiv 5 Induction 125 5.1 Ordinary Induction 125 5.2 Strong Induction 134 5.3 Strong Induction vs.
    [Show full text]