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1.
Let f be a transcendental meromorphic function. We propose a number of results concerning zeros and fixed points of the difference
g(z) = f(z + c) − f(z) and the divided difference g(z)/f(z). 相似文献
2.
For an analytic function f (z) on the unit disk |z| < 1 with f (0) = f′(0) − 1 = 0 and f (z) ≠ 0, 0 < |z| < 1, we consider the power deformation f c (z) = z(f (z)/z) c for a complex number c. We determine those values c for which the operator maps a specified class of univalent functions into the class of univalent functions. A little surprisingly, we will see that the set is described by the variability region of the quantity zf′(z)/ f (z), |z| < 1, for most of the classes that we consider in the present paper. As an unexpected by-product, we show boundedness of strongly spirallike functions. 相似文献
3.
E. G. Goluzina 《Journal of Mathematical Sciences》2010,166(2):222-224
The paper studies the region of values of the system {f(z
1), f(z
2), c
2},where z
j
, j=1, 2, are arbitrary fixed points of the disk |z|<1; f ∈ T, and the class T consists of all functions f(z) = z + c
2
z
2 + ··· regular in the disk |z| < 1 and satisfying the condition Im f(z)·Im z>0 for Im z > 0 for Im z ≠ 0. The region of values of f(z
1) in the subclass of functions f (z) ∈ T with prescribed values c
2 and f(z
2) is determined. Bibliography: 8 titles. 相似文献
4.
Yehoram Gordon 《Israel Journal of Mathematics》1966,4(3):177-188
GivenF(z),f
1(z), ..,f
n(z) defined on a finite point setE, and givenB — the set of generalised polynomials Σ
k
=1/n
a
kfk(z) — the definition of a juxtapolynomial is extended in the following manner: for a fixedλ(0<λ≦1),f(z) εB is called a generalizedλ-weak juxtapolynomial toF(z) onE if and only if there exists nog(z) εB for whichg(z)=F(z) wheneverf(z)=F(z) and |g(z)−F(z) |<λ|f(z)−F(z)| wheneverf(z)≠F(z). The properties of suchf(z) are investigated with particular attention given to the real case.
This note is an extension of a part of the author’s M.Sc. Thesis under the supervision of Prof. B. Grünbaum to whom the author
wishes to express his sincerest appreciation. The author also wishes to thank Dr. J. Lindenstrauss for his valuable remarks
in the preparation of this paper. 相似文献
5.
Zongming Guo 《Mathematische Nachrichten》2004,267(1):12-36
The structure of nontrivial nonnegative solutions to singularly perturbed quasilinear Dirichlet problems of the form –?Δpu = f(u) in Ω, u = 0 on ?Ω, Ω ? R N a bounded smooth domain, is studied as ? → 0+, for a class of nonlinearities f(u) satisfying f(0) = f(z1) = f(z2) = 0 with 0 < z1 < z2, f < 0 in (0, z1), f > 0 in (z1, z2) and f(u)/up–1 = –∞. It is shown that there are many nontrivial nonnegative solutions with spike‐layers. Moreover, the measure of each spike‐layer is estimated as ? → 0+. These results are applied to the study of the structure of positive solutions of the same problems with f changing sign many times in (0,∞). Uniqueness of a solution with a boundary‐layer and many positive intermediate solutions with spike‐layers are obtained for ? sufficiently small. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
S Ponnusamy 《Proceedings Mathematical Sciences》1994,104(2):397-411
Denote byS
* (⌕), (0≤⌕<1), the family consisting of functionsf(z)=z+a
2z2+...+anzn+... that are analytic and starlike of order ⌕, in the unit disc ⋎z⋎<1. In the present article among other things, with very
simple conditions on μ, ⌕ andh(z) we prove the f’(z) (f(z)/z)μ−1<h(z) implies f∈S*(⌕). Our results in this direction then admit new applications in the study of univalent functions. In many cases these results
considerably extend the earlier works of Miller and Mocanu [6] and others. 相似文献
7.
For an analytic function f (z) on the unit disk |z| < 1 with f (0) = f′(0) ? 1 = 0 and f (z) ≠ 0, 0 < |z| < 1, we consider the power deformation f c (z) = z(f (z)/z) c for a complex number c. We determine those values c for which the operator \({f \mapsto f_c}\) maps a specified class of univalent functions into the class of univalent functions. A little surprisingly, we will see that the set is described by the variability region of the quantity zf′(z)/ f (z), |z| < 1, for most of the classes that we consider in the present paper. As an unexpected by-product, we show boundedness of strongly spirallike functions. 相似文献
8.
A. M. Vershik 《Journal of Mathematical Sciences》2011,176(1):1-6
The paper studies the region of values of the system {c
2, c
3, f(z
1), f′(z
1)},where z
1 is an arbitrary fixed point of the disk |z| < 1; f ∈ T,and the class T consists of all the functions f(z) = z + c
2
z
2 + c
3z3 + ⋯ regular in the disk |z| < 1 that satisfy the condition Im z · Im f(z) > 0 for Im z ≠ 0. The region of values of f′(z
1) in the subclass of functions f ∈ T with prescribed values c
2, c
3, and f(z
1) is determined. Bibliography: 10 titles. 相似文献
9.
Mark L. Agranovsky 《Journal d'Analyse Mathématique》2011,113(1):305-329
Let C
t
= {z ∈ ℂ: |z − c(t)| = r(t), t ∈ (0, 1)} be a C
1-family of circles in the plane such that lim
t→0+
C
t
= {a}, lim
t→1−
C
t
= {b}, a ≠ b, and |c′(t)|2 + |r′(t)|2 ≠ 0. The discriminant set S of the family is defined as the closure of the set {c(t) + r(t)w(t), t ∈ [0, 1]}, where w = w(t) is the root of the quadratic equation ̅c′(t)w
2 + 2r′(t)w + c′(t) = 0 with |w| < 1, if such a root exists. 相似文献
10.
In this paper, we study orthogonal polynomials with respect to the bilinear form (f, g)
S
= V(f) A
V(g)
T
+ <u, f
(N)
g
(N)V(f) =(f(c
0), f "(c
0), ..., f
(n – 1)
0(c
0), ..., f(c
p
), f "(c
p
), ..., f
(n – 1)
p(c
p
))
u is a regular linear functional on the linear space P of real polynomials, c
0, c
1, ..., c
p
are distinct real numbers, n
0, n
1, ..., n
p
are positive integer numbers, N=n
0+n
1+...+n
p
, and A is a N × N real matrix with all its principal submatrices nonsingular. We establish relations with the theory of interpolation and approximation. 相似文献
11.
Austin Anderson 《Integral Equations and Operator Theory》2011,69(1):87-99
Our main result is a characterization of g for which the operator Sg(f)(z) = ò0z f¢(w)g(w) dw{S_g(f)(z) = \int_0^z f'(w)g(w)\, dw} is bounded below on the Bloch space. We point out analogous results for the Hardy space H
2 and the Bergman spaces A
p
for 1 ≤ p < ∞. We also show the companion operator Tg(f)(z) = ò0z f(w)g¢(w) dw{T_g(f)(z) = \int_0^z f(w)g'(w) \, dw} is never bounded below on H
2, Bloch, nor BMOA, but may be bounded below on A
p
. 相似文献
12.
Florian Luca 《Monatshefte für Mathematik》2005,233(2):239-256
In [2], it was shown that if a and b are multiplicatively independent integers and ɛ > 0, then the inequality gcd (an − 1,bn − 1) < exp(ɛn) holds for all but finitely many positive integers n. Here, we generalize the above result. In particular, we show that if f(x),f1(x),g(x),g1(x) are non-zero polynomials with integer coefficients, then for every ɛ > 0, the inequality
gcd (f(n)an+g(n), f1(n)bn+g1(n)) < exp(ne){\rm gcd}\, (f(n)a^n+g(n), f_1(n)b^n+g_1(n)) < \exp(n\varepsilon)
holds for all but finitely many positive integers n. 相似文献
13.
Amine El Sahili 《Journal of Graph Theory》2003,44(4):296-303
Consider two maps f and g from a set E into a set F such that f(x) ≠ g(x) for every x in E. Suppose that there exists a positive integer n such that for any element z in F either f?1(z) or g?1(z) has at most n elements. Then, E can be partitioned into 2n + 1 subsets E1, E2,…,E2n + 1 such that f(Ei)∩ g(Ei) = ?, 1 ≤ i ≤ 2n + 1. © 2003 Wiley Periodicals, Inc. J Graph Theory 44: 296–303, 2003 相似文献
14.
P. K. SAHO 《数学学报(英文版)》2005,21(5):1159-1166
In this paper, we determine the general solution of the functional equation f1 (2x + y) + f2(2x - y) = f3(x + y) + f4(x - y) + f5(x) without assuming any regularity condition on the unknown functions f1,f2,f3, f4, f5 : R→R. The general solution of this equation is obtained by finding the general solution of the functional equations f(2x + y) + f(2x - y) = g(x + y) + g(x - y) + h(x) and f(2x + y) - f(2x - y) = g(x + y) - g(x - y). The method used for solving these functional equations is elementary but exploits an important result due to Hosszfi. The solution of this functional equation can also be determined in certain type of groups using two important results due to Szekelyhidi. 相似文献
15.
In this paper, we prove the following result: Let f(z) and g(z) be two nonconstant meromorphic(entire) functions, n ≥ 11(n ≥ 6) a positive integer. If fn(z)f′(z) and gn(z)g′(z) have the same fixed-points, then either f(z) = c1ecz2, g(z) = c2e− cz2, where c1, c2, and c are three constants satisfying 4(c1c2)n + 1c2 = −1, or f(z) ≡ tg(z) for a constant t such that tn + 1 = 1. 相似文献
16.
Recently, C.-C. Yang and I. Laine have investigated finite order entire solutions f of nonlinear differential-difference equations of the form fn + L(z, f ) = h, where n ≥ 2 is an integer. In particular, it is known that the equation f(z)2 + q(z)f (z + 1) = p(z), where p(z), q(z) are polynomials, has no transcendental entire solutions of finite order. Assuming that Q(z) is also a polynomial and c ∈ C, equations of the form f(z)n + q(z)e Q(z) f(z + c) = p(z) do posses finite order entire solutions. A classification of these solutions in terms of growth and zero distribution will be given. In particular, it is shown that any exponential polynomial solution must reduce to a rather specific form. This reasoning relies on an earlier paper due to N. Steinmetz. 相似文献
17.
V. Mityushev 《Aequationes Mathematicae》1999,57(1):37-44
Summary. Local solutions of the functional equation¶¶zk f( z) = ?k=1nGk( z) f( skz ) +g( z) z{^\kappa} \phi \left( z\right) =\sum_{k=1}^nG_k\left( z\right) \phi \left( s_kz \right) +g\left( z\right) ¶with k > 0 \kappa > 0 and | sk| \gt 1 \left| s_k\right| \gt 1 are considered. We prove that the equation is solvable if and only if a certain system of k \kappa conditions on Gk (k = 1, 2, ... , n) and g is fulfilled. 相似文献
18.
Oscillation of Solutions of Linear Differential Equations 总被引:1,自引:0,他引:1
Ye Zhou LI Jun WANG 《数学学报(英文版)》2008,24(1):167-176
This paper is devoted to studying the growth problem, the zeros and fixed points distribution of the solutions of linear differential equations f″+e^-zf′+Q(z)f=F(z),whereQ(z)≡h(z)e^cz and c∈R. 相似文献
19.
彭志刚 《数学物理学报(B辑英文版)》1999,19(4):457-462
1Intr0ducti0nLetAden0tethesetofallfunctionsanalyticinA={z:Izl<1}.LetB={W:WEAandIW(z)l51}.Aisalocallyconvexlineaztop0l0gicalspacewithrespecttothetopologyofuniformconvergenceon`c0mpact8ubsetsofA-LetTh(c1,'tc.-1)={p(z):p(z)EA,Rop(z)>0,p(z)=1 clz czzz ' c.-lz"-l 4z" ',wherecl,',cn-1areforedcomplexconstants}.LetTh,.(b,,-..,b,-,)={p(z):P(z)'EAwithReP(z)>Oandp(z)=1 blz ' b.-lz"-l 4z" '-,wherebl,-'-jbu-1areffeedrealconstantsanddkarerealnumbersf0rk=n,n 1,'--}-LetTu(l1,'i'tI.-1)={… 相似文献
20.
Laurent Padé-Chebyshev rational approximants,A
m
(z,z
−1)/B
n
(z, z
−1), whose Laurent series expansions match that of a given functionf(z,z
−1) up to as high a degree inz, z
−1 as possible, were introduced for first kind Chebyshev polynomials by Clenshaw and Lord [2] and, using Laurent series, by
Gragg and Johnson [4]. Further real and complex extensions, based mainly on trigonometric expansions, were discussed by Chisholm
and Common [1]. All of these methods require knowledge of Chebyshev coefficients off up to degreem+n. Earlier, Maehly [5] introduced Padé approximants of the same form, which matched expansions betweenf(z,z
−1)B
n
(z, z
−1)). The derivation was relatively simple but required knowledge of Chebyshev coefficients off up to degreem+2n. In the present paper, Padé-Chebyshev approximants are developed not only to first, but also to second, third and fourth
kind Chebyshev polynomial series, based throughout on Laurent series representations of the Maehly type. The procedures for
developing the Padé-Chebyshev coefficients are similar to that for a traditional Padé approximant based on power series [8]
but with essential modifications. By equating series coefficients and combining equations appropriately, a linear system of
equations is successfully developed into two sub-systems, one for determining the denominator coefficients only and one for
explicitly defining the numerator coefficients in terms of the denominator coefficients. In all cases, a type (m, n) Padé-Chebyshev approximant, of degreem in the numerator andn in the denominator, is matched to the Chebyshev series up to terms of degreem+n, based on knowledge of the Chebyshev coefficients up to degreem+2n. Numerical tests are carried out on all four Padé-Chebyshev approximants, and results are outstanding, with some formidable
improvements being achieved over partial sums of Laurent-Chebyshev series on a variety of functions. In part II of this paper
[7] Padé-Chebyshev approximants of Clenshaw-Lord type will be developed for the four kinds of Chebyshev series and compared
with those of the Maehly type. 相似文献