Inequalities for Maximum Modulus of Rational Functions with Prescribed Poles


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Authors: S. L. WALI

DOI: 10.46793/KgJMat2306.865W

Abstract:

In this paper we prove some results concerning the rational functions with prescribed poles and restricted zeros. These results in fact generalize or strengthen some known inequalities for rational functions with prescribed poles and in turn produce new results besides the refinements of some known polynomial inequalities. Our method of proof may be useful for proving other inequalities for polynomials and rational functions.



Keywords:

Rational functions, polynomials, Schwarz lemma, inequalities, polar derivative.



References:

[1]   N. C. Ankeny and T. J. Rivlin, On a theorem of S. Bernstein, Pacific J. Math. 5(2) (1955), 849–852.

[2]   A. Aziz and Q. G. Mohammad, Growth of polynomials, with zeros outside a circle, Proc. Amer. Math. Soc. 81(4) (1981), 549–553. https://doi.org/10.2307/2044157

[3]   A. Aziz and N. A. Rather, Growth of maximum modulus of rational functions with prescribed poles, Math. Inequal. Appl. 2 (1999), 165–173.

[4]   A. Aziz and W. M. Shah, Some properties of rational functions with prescribed poles and restricted zeros, Math. Balkanica (N.S) 18 (2004), 33–40.

[5]   S. Bernstein, Sur la limitation des dérivées des polynomes, C. R. Math. Acad. Sci. Paris 190 (1930), 338–340.

[6]   V. N. Dubinin, Applications of the Schwarz lemma to inequalities for entire functions with constraints on zeros, J. Math. Sci. (N.Y) 143(3) (2007), 3069–3076. https://doi.org/10.1007/s10958-007-0192-4

[7]   N. K. Govil and R. N. Mohapatra, Inequalities for Maximum Modulus of Rational Functions with Prescribed Poles, Dekker, New York, 1998.

[8]   S. G. Krantz, The Schwarz bemma at the boundary, Complex Var. Elliptic Equ. 56(5) (2011), 455–468. https://doi.org/10.1080/17476931003728438

[9]   P. D. Lax, Proof of a conjecture of P. Erdös on the derivative of a polynomial, Bull. Amer. Math. Soc. 50 (1944), 509–513. https://doi.org/10.1090/s0002-9904-1944-08177-9

[10]   X. Li, R. N. Mohapatra and R. S. Rodriguez, Bernstien-type inequalities for rational functions with prescribed poles, J. London. Math. Soc. 1 (1995), 523–531. https://doi.org/10.1112/jlms/51.3.523

[11]   M. A. Malik, On the derivative of a polynomial, J. London. Math. Soc. 1 (1969), 57–60. https://doi.org/10.1112/jlms/s2-1.1.57

[12]   R. Osserman, A sharp Schwarz inequality on the boundary for functions regular in the disk, Proc. Amer. Math. Soc. 12 (2000), 3513–3517. https://doi.org/10.1090/s0002-9939-1988.0928994-0

[13]   W. M. Shah, A generalisation of a theorem of Paul Túran, J. Ramanujan Math. Soc. 11(1) (1996), 67–72.

[14]   P. Turán, Über die ableitung von polynomen, Compos. Math. 7 (1939), 89–95.

[15]   S. L. Wali and W. M. Shah, Applications of the Schwarz lemma to inequalities for rational functions with prescribed poles. J. Anal. 25 (2017), 43–53. https://doi:10.1007/s41478-016-0025-2