DOCSLIB.ORG

Introduction to Differential Equations

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Introduction to Differential Equations Introduction to Differential Equations J. M. Veal, Ph. D. version 13.08.30 Contents 4 Series Solutions of Linear Equations 4 4.1 Solutions About Ordinary Points . 4 1 Introduction to Differential Equations 2 4.2 Solutions About Singular Points . 4 1.1 Definitions and Terminology . 2 4.3 Special Functions (in Brief) . 5 1.2 Initial-Value Problems . 2 1.3 Differential Equations as Mathematical Models . 2 5 Systems of Linear First-Order Differential Equations 5 5.1 Preliminary Theory . 5 2 First-Order Differential Equations 2 5.2 Homogeneous Linear Systems with Constant Coefficients . 5 2.1 Separable Variables . 2 2.2 Linear Equations . 2 6 The Laplace Transform 5 2.3 Exact Equations . 2 6.1 Definition of the Laplace Transform . 5 2.4 Solutions by Substitutions . 2 6.2 Inverse Transform and Transforms of Derivatives . 6 6.3 Translation Theorems . 6 3 Higher-Order Differential Equations 3 6.4 tn Factors and Convolution . 6 3.1 Preliminary Theory: Linear Equations . 3 6.5 Dirac Delta Function . 6 3.2 Reduction of Order . 3 3.3 Homogeneous Linear Equations with Constant Coefficients . 3 7 Modeling with Differential Equations 7 3.4 Undetermined Coefficients { Annihilator Approach . 3 7.1 Linear Models . 7 3.5 Variation of Parameters . 4 7.2 Nonlinear Models . 7 3.6 Cauchy-Euler Equation . 4 7.3 Modeling with Systems of Differential Equations . 7 A Transforms & Inverse Transforms 8 1 J. M. Veal, Introduction to Differential Equations 2 1 Introduction to Differential Equations • singular points. explanation 1.1 Definitions and Terminology • reciprocal. example • differential equations, type, order, linearity. explanation 2.3 Exact Equations • solution, interval, trivial, explicit/implicit, families, singular. explanation • differential, exact equation. explanation 1.2 Initial-Value Problems • criterion for an exact differential. theorem, proof • existence of a unique solution for first-order. theorem • METHOD { Exact Equation: 1.3 Differential Equations as Mathematical Models BM BN Mpx; yq dx Npx; yq dy 0; with • physics, chemistry, biology, engineering. examples By Bx { integrate M wrto x, take derivative wrto y, set equal to N, find gpyq 2 First-Order Differential Equations 2.1 Separable Variables 2.4 Solutions by Substitutions • METHOD { Separable Equation: • homogeneous function, homogeneous differential equation. explanation dy • METHOD { Homogeneous Equation: gpxq hpyq dx Mpx; yq dx Npx; yq dy 0; { separate variables p q α p q • losing a solution. example with M tx; ty t M x; y α • dissimilar expressions. example and Nptx; tyq t Npx; yq { substitute y ux and dy u dx x du (or substitute x vy and 2.2 Linear Equations dx v dy y dv) • linear, homogeneous, nonhomogeneous, standard form. explanation • METHOD { Bernoulli's Equation: • property, variation of parameters, integrating factor. explanation, deriva- dy tions P pxqy fpxqyn dx • METHOD { Linear Equation: { for n 0; 1, substitute u y1¡n dy a1pxq a0pxqy gpxq dx • METHOD { Equation Can Be Reduced To Separable: { find standard form, multiply by integrating factor, l.h.s. is ³ dy d p q fpAx By Cq; with B 0 re P x dxys, integrate dx dx • constant of integration. discussion { substitute u Ax By C J. M. Veal, Introduction to Differential Equations 3 3 Higher-Order Differential Equations 3.3 Homogeneous Linear Equations with Constant Coefficients 3.1 Preliminary Theory: Linear Equations • second-order with constant coefficients, exponential solution. explanation • auxiliary equation, three cases of roots, Euler's formula. explanation • existence of a unique solution. theorem • METHOD { Homogeneous Linear Second-Order Equation with Constant • boundary value problem. discussion Coefficients: 2 1 a2y a1y a0y 0 • homogeneous, nonhomogeneous. explanation { ay2 by1 cy 0, leads to auxiliary equation am2 bm c 0, • nth-order differential operator, linear operator. explanation three cases for m1 & m2 m x m x { distinct real roots: y c1e 1 c2e 2 , repeated real roots: y m x m x αx • superposition principle { homogeneous equations. theorem, proof, corol- c1e 1 c2xe 1 , conjugate complex roots: y e pc1 cos βx laries c2 sin βxq • linear dependence/independence, Wronskian. definitions • METHOD { Homogeneous Linear Higher-Order Equation with Constant Coefficients: pnq pn¡1q 2 1 • criterion for linearly independent solutions. theorem any an¡1y ¤ ¤ ¤ a2y a1y a0y 0 • fundamental set of solutions. definition { find at least one root of auxiliary equation via algebraic guess { long division, guess again, repeat until arrive at second-order • general solution { homogeneous equations. theorem, proof • multiplicity. explanation 3.4 Undetermined Coefficients { Annihilator Approach Exam 1 covers material up to here. • nth-order differential operator, linear operator. review • factoring operators, annihilator operator. explanation 3.2 Reduction of Order • METHOD { Nonhomogeneous Linear Second-Order or Higher-Order Equation with Constant Coefficients: • linear second-order homogeneous equation, standard form. explanation pnq pn¡1q 2 1 any an¡1y ¤ ¤ ¤ a2y a1y a0y gpxq • general case, formula, check. derivation { find complementary function, yc [i.e., solve corresponding homoge- neous equation Lpyq 0] • METHOD { Homogeneous Linear Second-Order Equation { Second Solu- p ¡ qn n¡1 αx tion: { D α annihilates x e ¡ 2 1 { rD2 ¡ 2αD pα2 β2qsn annihilates xn 1eαx cos βx and/or a2pxqy a1pxqy a0pxqy 0 xn¡1eαx sin βx 1 p q p q { find standard form, substitute y upxqy1pxq and corresponding y { operate with L1 on both sides of L y g x 2 1 and y , substitute w u { find general solution, y, to L1Lpyq 0 » ³ ¡ p q ¡ p q e P x dx { given yp y yc, solve for coefficients in yp by substituting yp into { y2 y1 x 2p q dx yx x Lpyq gpxq J. M. Veal, Introduction to Differential Equations 4 3.5 Variation of Parameters 4 Series Solutions of Linear Equations • assumptions. explanation 4.1 Solutions About Ordinary Points • METHOD { Nonhomogeneous Linear Second-Order Equation: • power series. review 2 1 a2pxqy a1pxqy a0pxqy gpxq • ordinary point, singular point. definition { find standard form, find yc (must be given yc if nonconstant coeffi- cients), substitute yp u1pxqy1pxq u2pxqy2pxq and corresponding • existence of power series solution. theorem 1 2 1 1 y and y , assume u1 & u2 are such that u1y1 u2y2 0, arrive at 1 1 1 1 p q u1y1 u2y2 f x • METHOD { Homogeneous Linear Second-Order Equation About an Or- { Cramer's rule gives u1 W {W and u1 W {W , where W (the dinary Point: 1 1 2 2 2 1 Wronskian), W , and W are given by a2pxqy a1pxqy a0pxqy 0 § 1 § 2 § § § § § y y § § 0 y § § y 0 § § 1 2 § § 2 § § 1 § { If P pxq and Qpxq of standard form are analytic at x0, then x0 is an W § 1 1 § W1 § p q 1 § W2 § 1 p q § y1 y2 f x y2 y1 f x ordinary point ° { integrate to find u & u and hence y and then have y y y 8 p ¡ qn 1 2 1 2 p c p { substitute y n0 cn x x0 and corresponding y and y • higher-order equations. explanation { add all series: ensure powers of x are in phase and ensure summation indices start with same number ° 3.6 Cauchy-Euler Equation 8 p ¡ qk { use identity property (if k0 ck x a 0, then ck 0 for all k) • second-order, xm solution. explanation to establish recurrence relation, find ck for increasing k until patterns are recognizable • auxiliary equation, three cases of roots, note before using Euler's formula. { group all c terms and c terms to find y c y pxq c y pxq explanation 0 1 0 1 1 2 { for three-term recurrence relation, first let c1 0 to find y1pxq and • METHOD { Homogeneous Second-Order Cauchy-Euler Equation: second let c0 0 to find y2pxq ax2y2 bxy1 cy 0 { ax2y2 bxy1 cy 0, leads to auxiliary equation am2 pb¡aqm c 4.2 Solutions About Singular Points 0, three cases for m1 & m2 • regular and irregular singular points. definition m m { distinct real roots: y c1x 1 c2x 2 , repeated real roots: y m m α c1x 1 c2x 1 ln x, conjugate complex roots: y x rc1 cos pβ ln xq • Frobenius' Theorem. c2 sin pβ ln xqs • indicial equation, indicial roots. explanation • reduction to constant coefficients. explanation • METHOD { Homogeneous Linear Second-Order Equation About a Regu- • METHOD (alternate): lar Singular Point (Method of Frobenius): { substitute x et, solve, resubstitute t ln x. 2 1 a2pxqy a1pxqy a0pxqy 0 2 Exam 2 covers material between Exam 1 and here. { If ppxq px ¡ x0qP pxq and qpxq px ¡ x0q Qpxq (where P & Q are from standard form) are analytic at x0, then x0 is an regular singular point J. M. Veal, Introduction to Differential Equations 5 { substitute • general solution { homogeneous systems. theorem ¸8 ¸8 r n n r • general solution { nonhomogeneous systems. theorem y px ¡ x0q cnpx ¡ x0q cnpx ¡ x0q n0 n0 5.2 Homogeneous Linear Systems with Constant Coefficients and corresponding y1 and y2 • eigenvalue, eigenvector. explanation { add all series: ensure powers of x are in phase and ensure summation indices start with same number • general solution { homogeneous systems. theorem, example { equate to 0 the total coefficient of the lowest power of x, solve (indicial • Gauss-Jordan elimination. explanation equation) for roots (two values of r) ° 8 p ¡ qk • METHOD { Homogeneous Linear First-Order System: { use identity property (if k0 ck x a 0, then ck 0 for all k) to ¤ ¤ ¤ establish two recurrence relations using (one for each root of indicial x1ptq a11ptq a12ptq ¤ ¤ ¤ a1nptq x1ptq ¦ ¦ ¦ equation), find ck for increasing k until patterns are recognizable ¦ x2ptq ¦ a21ptq a22ptq ¤ ¤ ¤ a2nptq ¦ x2ptq d p q p q ¦ . ¦ . ¦ . { omit c0 since y C1y1 x C2y2 x dt ¥ . ¥ . ¥ . xnptq an1ptq an2ptq ¤ ¤ ¤ annptq xnptq 4.3 Special Functions (in Brief) (or, equivalently, X1 AX) • Bessel's equation of order ν.
Load more

Recommended publications
  • FUNCTIONAL ANALYSIS 1. Banach and Hilbert Spaces in What
    FUNCTIONAL ANALYSIS PIOTR HAJLASZ 1. Banach and Hilbert spaces In what follows K will denote R of C. Definition. A normed space is a pair (X, k · k), where X is a linear space over K and k · k : X → [0, ∞) is a function, called a norm, such that (1) kx + yk ≤ kxk + kyk for all x, y ∈ X; (2) kαxk = |α|kxk for all x ∈ X and α ∈ K; (3) kxk = 0 if and only if x = 0. Since kx − yk ≤ kx − zk + kz − yk for all x, y, z ∈ X, d(x, y) = kx − yk defines a metric in a normed space. In what follows normed paces will always be regarded as metric spaces with respect to the metric d. A normed space is called a Banach space if it is complete with respect to the metric d. Definition. Let X be a linear space over K (=R or C). The inner product (scalar product) is a function h·, ·i : X × X → K such that (1) hx, xi ≥ 0; (2) hx, xi = 0 if and only if x = 0; (3) hαx, yi = αhx, yi; (4) hx1 + x2, yi = hx1, yi + hx2, yi; (5) hx, yi = hy, xi, for all x, x1, x2, y ∈ X and all α ∈ K. As an obvious corollary we obtain hx, y1 + y2i = hx, y1i + hx, y2i, hx, αyi = αhx, yi , Date: February 12, 2009. 1 2 PIOTR HAJLASZ for all x, y1, y2 ∈ X and α ∈ K. For a space with an inner product we define kxk = phx, xi . Lemma 1.1 (Schwarz inequality).
    [Show full text]
  • Semi-Indefinite-Inner-Product and Generalized Minkowski Spaces
    Semi-indefinite-inner-product and generalized Minkowski spaces A.G.Horv´ath´ Department of Geometry, Budapest University of Technology and Economics, H-1521 Budapest, Hungary Nov. 3, 2008 Abstract In this paper we parallelly build up the theories of normed linear spaces and of linear spaces with indefinite metric, called also Minkowski spaces for finite dimensions in the literature. In the first part of this paper we collect the common properties of the semi- and indefinite-inner-products and define the semi-indefinite- inner-product and the corresponding structure, the semi-indefinite-inner- product space. We give a generalized concept of Minkowski space embed- ded in a semi-indefinite-inner-product space using the concept of a new product, that contains the classical cases as special ones. In the second part of this paper we investigate the real, finite dimen- sional generalized Minkowski space and its sphere of radius i. We prove that it can be regarded as a so-called Minkowski-Finsler space and if it is homogeneous one with respect to linear isometries, then the Minkowski- Finsler distance its points can be determined by the Minkowski-product. MSC(2000):46C50, 46C20, 53B40 Keywords: normed linear space, indefinite and semi-definite inner product, arXiv:0901.4872v1 [math.MG] 30 Jan 2009 orthogonality, Finsler space, group of isometries 1 Introduction 1.1 Notation and Terminology concepts without definition: real and complex vector spaces, basis, dimen- sion, direct sum of subspaces, linear and bilinear mapping, quadratic forms, inner (scalar) product, hyperboloid, ellipsoid, hyperbolic space and hyperbolic metric, kernel and rank of a linear mapping.
    [Show full text]
  • On the Continuity of Fourier Multipliers on the Homogeneous Sobolev Spaces
    R AN IE N R A U L E O S F D T E U L T I ’ I T N S ANNALES DE L’INSTITUT FOURIER Krystian KAZANIECKI & Michał WOJCIECHOWSKI On the continuity of Fourier multipliers on the homogeneous Sobolev spaces . 1 d W1 (R ) Tome 66, no 3 (2016), p. 1247-1260. <http://aif.cedram.org/item?id=AIF_2016__66_3_1247_0> © Association des Annales de l’institut Fourier, 2016, Certains droits réservés. Cet article est mis à disposition selon les termes de la licence CREATIVE COMMONS ATTRIBUTION – PAS DE MODIFICATION 3.0 FRANCE. http://creativecommons.org/licenses/by-nd/3.0/fr/ L’accès aux articles de la revue « Annales de l’institut Fourier » (http://aif.cedram.org/), implique l’accord avec les conditions générales d’utilisation (http://aif.cedram.org/legal/). cedram Article mis en ligne dans le cadre du Centre de diffusion des revues académiques de mathématiques http://www.cedram.org/ Ann. Inst. Fourier, Grenoble 66, 3 (2016) 1247-1260 ON THE CONTINUITY OF FOURIER MULTIPLIERS . 1 d ON THE HOMOGENEOUS SOBOLEV SPACES W1 (R ) by Krystian KAZANIECKI & Michał WOJCIECHOWSKI (*) Abstract. — In this paper we prove that every Fourier multiplier on the ˙ 1 d homogeneous Sobolev space W1 (R ) is a continuous function. This theorem is a generalization of the result of A. Bonami and S. Poornima for Fourier multipliers, which are homogeneous functions of degree zero. Résumé. — Dans cet article, nous prouvons que chaque multiplicateur de Fou- ˙ 1 d rier sur l’espace homogène W1 (R ) de Sobolev est une fonction continue. Notre théorème est une généralisation du résultat de A.
    [Show full text]
  • Weak Convergence of Asymptotically Homogeneous Functions of Measures
    h’on,inec,r ~ndysrr, Theory. Methods & App/;cmonr. Vol. IS. No. I. pp. I-16. 1990. 0362-546X/90 13.M)+ .OO Printed in Great Britain. 0 1990 Pergamon Press plc WEAK CONVERGENCE OF ASYMPTOTICALLY HOMOGENEOUS FUNCTIONS OF MEASURES FRANGOISE DEMENGEL Laboratoire d’Analyse Numerique, Universite Paris-Sud, 91405 Orsay, France and JEFFREY RAUCH* University of Michigan, Ann Arbor, Michigan 48109, U.S.A. (Received 28 April 1989; received for publication 15 September 1989) Key words and phruses: Functions of measures, weak convergence, measures. INTRODUCTION FUNCTIONS of measures have already been introduced and studied by Goffman and Serrin [8], Reschetnyak [lo] and Demengel and Temam [5]: especially for the convex case, some lower continuity results for the weak tolopology (see [5]) permit us to clarify and solve, from a mathematical viewpoint, some mechanical problems, namely in the theory of elastic plastic materials. More recently, in order to study weak convergence of solutions of semilinear hyperbolic systems, which arise from mechanical fluids, we have been led to answer the following ques- tion: on what conditions on a sequence pn of bounded measures have we f(~,) --*f(p) where P is a bounded measure and f is any “function of a measure” (not necessarily convex)? We answer this question in Section 1 when the functions f are homogeneous, and in Section 2 for sublinear functions; the general case of asymptotically homogeneous function is then a direct consequence of the two previous cases! An extension to x dependent functions is described in Section 4. In the one dimensional case, we give in proposition 3.3 a criteria which is very useful in practice, namely for the weak continuity of solutions measures of hyperbolic semilinear systems with respect to weakly convergent Cauchy data.
    [Show full text]
  • G = U Ytv2
    PROCEEDINGS of the AMERICAN MATHEMATICAL SOCIETY Volume 81, Number 1, January 1981 A CHARACTERIZATION OF MINIMAL HOMOGENEOUS BANACH SPACES HANS G. FEICHTINGER Abstract. Let G be a locally compact group. It is shown that for a homogeneous Banach space B on G satisfying a slight additional condition there exists a minimal space fimm in the family of all homogeneous Banach spaces which contain all elements of B with compact support. Two characterizations of Bm¡1¡aie given, the first one in terms of "atomic" representations. The equivalence of these two characterizations is derived by means of certain (bounded) partitions of unity which are of interest for themselves. Notations. In the sequel G denotes a locally compact group. \M\ denotes the (Haar) measure of a measurable subset M G G, or the cardinality of a finite set. ®(G) denotes the space of continuous, complex-valued functions on G with compact support (supp). For y G G the (teft) translation operator ly is given by Lyf(x) = f(y ~ xx). A translation invariant Banach space B is called a homogeneous Banach space (in the sense of Katznelson [9]) if it is continuously embedded into the topological vector space /^(G) of all locally integrable functions on G, satisfies \\Lyf\\B= 11/11,for all y G G, and lim^iy-- f\\B - 0 for all / G B (hence, as usual, two measurable functions coinciding l.a.e. are identified). If, furthermore, B is a dense subspace of LX(G) it is called a Segal algebra (in the sense of Reiter [15], [16]). Any homogeneous Banach space is a left L'((7)-Banach- module with respect to convolution, i.e./ G B, h G LX(G) implies h */ G B, and \\h */\\b < ll*Uill/IJi» m particular any Segal algebra is a Banach ideal of LX(G).
    [Show full text]
  • Homogeneous Length Functions on Groups
    HOMOGENEOUS LENGTH FUNCTIONS ON GROUPS D.H.J. POLYMATH Abstract. A pseudo-length function defined on an arbitrary group G “ pG; ¨; e; p q´1q is a map ` : G Ñ r0; `8q obeying `peq “ 0, the symmetry property `px´1q “ `pxq, and the triangle inequality `pxyq ¤ `pxq ` `pyq for all x; y P G. We consider pseudo-length functions which saturate the triangle inequality whenever x “ y, or equivalently those n that are homogeneous in the sense that `px q “ n `pxq for all n P N. We show that this implies that `prx; ysq “ 0 for all x; y P G. This leads to a classification of such pseudo-length functions as pullbacks from em- beddings into a Banach space. We also obtain a quantitative version of our main result which allows for defects in the triangle inequality or the homogeneity property. 1. Introduction Let G “ pG; ¨; e; p q´1q be a group (written multiplicatively, with identity element e). A pseudo-length function on G is a map ` : G Ñ r0; `8q that obeys the properties ‚ `peq “ 0, ‚ `px´1q “ `pxq, ‚ `pxyq ¤ `pxq ` `pyq for all x; y P G. If in addition we have `pxq ¡ 0 for all x P Gzteu, we say that ` is a length function. By setting dpx; yq :“ `px´1yq, it is easy to see that pseudo-length functions (resp. length functions) are in bijection with left-invariant pseudometrics (resp. left-invariant metrics) on G. From the axioms of a pseudo-length function it is clear that one has the upper bound `pxnq ¤ |n| `pxq for all x P G and n P Z.
    [Show full text]
  • Homogeneous Functions
    Optimization. A first course of mathematics for economists Xavier Martinez-Giralt Universitat Autonoma` de Barcelona [email protected] I.3.- Differentiability OPT – p.1/91 Differentiation and derivative Definitions A function f : A IR IR is differentiable at a point x0 A if the limit ⊂ → ∈ f(xo+h) f(x0) f ′(x0) = limh 0 h− exists. Equivalently, → ′ f(x0+h) f(x0) f (x0)h limh 0 − h − = 0 or → ′ f(x) f(x ) f (x )(x x ) | − 0 − 0 − 0 | limx x0 x x = 0. → | − 0| n m A function f : A IR IR is differentiable at a point x0 A if we can find a linear⊂ function→ Df(x ) : IRn IRm (that we∈ 0 → refer to as the derivative of f at x0) such that f(x) [f(x )+ Df(x )(x x )] lim k − 0 0 − 0 k = 0 x x0 x x → k − 0k If f is differentiable x A, we say that f is differentiable inA. ∀ ∈ Derivative is the slope of the linear approximation of f at x0. OPT – p.2/91 Differentiability- Illustration y = f(x0) + Df (x0)( x − x0) ′ y = f(x0) + f (x0)( x − x0) x2 f f(x) x2 x 0 x1 x0 x1 OPT – p.3/91 Differentiation and derivative (2) Some theorems m Theorem 1: Let f : A IR be differentiable at x0 A. Assume A IRn is an→ open set. Then, there is a unique∈ linear ⊂ approximation Df(x0) to f at x0. Recall some one-dimensional results Theorem 2 (Fermat): Let f : (a,b) IR be differentiable at → c (a,b).
    [Show full text]
  • Singular Integrals on Homogeneous Spaces and Some Problems Of
    ANNALI DELLA SCUOLA NORMALE SUPERIORE DI PISA Classe di Scienze A. KORÁNYI S. VÁGI Singular integrals on homogeneous spaces and some problems of classical analysis Annali della Scuola Normale Superiore di Pisa, Classe di Scienze 3e série, tome 25, no 4 (1971), p. 575-648 <http://www.numdam.org/item?id=ASNSP_1971_3_25_4_575_0> © Scuola Normale Superiore, Pisa, 1971, 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/ SINGULAR INTEGRALS ON HOMOGENEOUS SPACES AND SOME PROBLEMS OF CLASSICAL ANALYSIS A. KORÁNYI and S. VÁGI CONTENTS Introduction. Part I. General theory. 1. Definitions and basic facts. 2. The main result on LP -continuity. 3. An L2-theorem. 4. Preservation of Lipschitz classes. 5. Homogeneous gauges and kernel Part 11. Applications. 6. The Canohy-Szego integral for the generalized halfplane D. 7. The Canchy-Szego integral for the complex unit ball. 8. The functions of Littlewood-Paley and Lusin on D. 9. The Riesz transform on Introduction. In this paper we generalize some classical results of Calderon and Zygmund to the context of homogeneous spaces of locally compact groups and use these results to solve certain problems of classical type which can not be dealt with by the presently existing versions of the theory of sin- gular integrals.
    [Show full text]
  • On the Degree of Homogeneous Bent Functions
    On the degree of homogeneous bent functions Qing-shu Meng, Huan-guo Zhang, Min Yang, and Jing-song Cui School of Computer, Wuhan University, Wuhan 430072, Hubei, China [email protected] Abstract. It is well known that the degree of a 2m-variable bent func- tion is at most m: However, the case in homogeneous bent functions is not clear. In this paper, it is proved that there is no homogeneous bent functions of degree m in 2m variables when m > 3; there is no homogenous bent function of degree m ¡ 1 in 2m variables when m > 4; Generally, for any nonnegative integer k, there exists a positive integer N such that when m > N, there is no homogeneous bent functions of de- gree m¡k in 2m variables. In other words, we get a tighter upper bound on the degree of homogeneous bent functions. A conjecture is proposed that for any positive integer k > 1, there exists a positive integer N such that when m > N, there exists homogeneous bent function of degree k in 2m variables. Keywords: cryptography, homogeneous bent functions, Walsh transform. 1 Introduction Boolean functions have been of great interest in many fields of engineering and science, especially in cryptography. Boolean functions with highest possible non- linearity are called bent functions, which was first proposed in [11] by Rothaus. As bent function has equal Hamming distance to all affine functions, it plays an important role in cryptography (in stream-ciphers, for instance), error cor- recting coding, and communication (modified into sequence used in CDMA[6]). Many works[5, 11, 1, 2, 13, 14] have been done in construction of bent functions and classification of bent functions.
    [Show full text]
  • A Note on Actions of Some Monoids 3
    A note on actions of some monoids∗ Michał Jó´zwikowski† and Mikołaj Rotkiewicz‡, June 21, 2021 Abstract Smooth actions of the multiplicative monoid (R, ) of real numbers on manifolds lead to an alternative, and for some reasons simpler, definitions· of a vector bundle, a double vector bundle and related structures like a graded bundle (Grabowski and Rotkiewicz (2011) [GR11]). For these reasons it is natural to study smooth actions of certain monoids closely related with the monoid (R, ). Namely, we discuss geometric structures naturally related with: smooth and holomorphic actions· of the monoid of multiplicative complex numbers, smooth actions of the monoid of second jets of punctured maps (R, 0) (R, 0), smooth actions of the monoid of real 2 by 2 matrices and smooth actions of the multiplicative→ reals on a supermanifold. In particular cases we recover the notions of a holomorphic vector bundle, a complex vector bundle and a non-negatively graded manifold. MSC 2010: 57S25 (primary), 32L05, 58A20, 58A50 (secondary) Keywords: Monoid action,Graded bundle, Graded manifold, Homogeneity structure, Holomorphic bundle, Supermanifold 1 Introduction Motivation Our main motivation to undertake this study were the results of Grabowski and Rotkie- wicz [GR09, GR11] concerning action of the multiplicative monoid of real numbers (R, ) on smooth · manifolds. In the first of the cited papers the authors effectively characterized these smooth actions of (R, ) on a manifold M which come from homotheties of a vector bundle structure on M. In particular, · it turned out that the addition on a vector bundle is completely determined by the multiplication by reals (yet the smoothness of this multiplication at 0 R is essential).
    [Show full text]
  • Differential Equations and Linear Algebra
    Differential Equations and Linear Algebra Jason Underdown December 8, 2014 Contents Chapter 1. First Order Equations1 1. Differential Equations and Modeling1 2. Integrals as General and Particular Solutions5 3. Slope Fields and Solution Curves9 4. Separable Equations and Applications 13 5. Linear First{Order Equations 20 6. Application: Salmon Smolt Migration Model 26 7. Homogeneous Equations 28 Chapter 2. Models and Numerical Methods 31 1. Population Models 31 2. Equilibrium Solutions and Stability 34 3. Acceleration{Velocity Models 39 4. Numerical Solutions 41 Chapter 3. Linear Systems and Matrices 45 1. Linear and Homogeneous Equations 45 2. Introduction to Linear Systems 47 3. Matrices and Gaussian Elimination 50 4. Reduced Row{Echelon Matrices 53 5. Matrix Arithmetic and Matrix Equations 53 6. Matrices are Functions 53 7. Inverses of Matrices 57 8. Determinants 58 Chapter 4. Vector Spaces 61 i ii Contents 1. Basics 61 2. Linear Independence 64 3. Vector Subspaces 65 4. Affine Spaces 65 5. Bases and Dimension 66 6. Abstract Vector Spaces 67 Chapter 5. Higher Order Linear Differential Equations 69 1. Homogeneous Differential Equations 69 2. Linear Equations with Constant Coefficients 70 3. Mechanical Vibrations 74 4. The Method of Undetermined Coefficients 76 5. The Method of Variation of Parameters 78 6. Forced Oscillators and Resonance 80 7. Damped Driven Oscillators 84 Chapter 6. Laplace Transforms 87 1. The Laplace Transform 87 2. The Inverse Laplace Transform 92 3. Laplace Transform Method of Solving IVPs 94 4. Switching 101 5. Convolution 102 Chapter 7. Eigenvalues and Eigenvectors 105 1. Introduction to Eigenvalues and Eigenvectors 105 2.
    [Show full text]
  • An Explicit Formula of Hessian Determinants of Composite Functions and Its Applications
    Kragujevac Journal of Mathematics Volume 36 Number 1 (2012), Pages 27{39. AN EXPLICIT FORMULA OF HESSIAN DETERMINANTS OF COMPOSITE FUNCTIONS AND ITS APPLICATIONS BANG-YEN CHEN Abstract. The determinants of Hessian matrices of di®erentiable functions play important roles in many areas in mathematics. In practice it can be di±cult to compute the Hessian determinants for functions with many variables. In this article we derive a very simple explicit formula for the Hessian determi- nants of composite functions of the form: f(x) = F (h1(x1) + ¢ ¢ ¢ + hn(xn)): Several applications of the Hessian determinant formula to production functions in microeconomics are also given in this article. 1. Introduction The Hessian matrix H(f) (or simply the Hessian) is the square matrix (fij) of second-order partial derivatives of a function f. If the second derivatives of f are all continuous in a neighborhood D, then the Hessian of f is a symmetric matrix throughout D. Because f is often clear from context, H(f)(x) is frequently shortened to simply H(x). Hessian matrices of functions play important roles in many areas in mathematics. For instance, Hessian matrices are used in large-scale optimization problems within Newton-type methods because they are the coe±cient of the quadratic term of a local Taylor expansion of a function, i.e., 1 f(x + ¢x) ¼ f(x) + J(x)¢x + ¢xT H(x)¢x; 2 where J is the Jacobian matrix, which is a vector (the gradient for scalar-valued functions). Another example is the application of Hessian matrices to Morse theory Key words and phrases.
    [Show full text]