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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2021 Volume 503, Pages 57–71 (Mi znsl7099)

This article is cited in 1 paper

Logarithmically absolutely monotone trigonometric functions

O. L. Vinogradov

St. Petersburg State University, Mathematics and Mechanics Faculty

Abstract: We study absolute monotonicity and logarithmic absolute monotonicity for functions
$$ f(z)=\dfrac{\cos{\alpha_1z}\cdot\ldots\cdot\cos{\alpha_Mz} \cdot\sin{\beta_1z}\cdot\ldots\cdot\sin{\beta_Nz}} {\cos{\alpha'_1z}\cdot\ldots\cdot\cos{\alpha'_{M'}z} \cdot\sin{\beta'_1z}\cdot\ldots\cdot\sin{\beta'_{N'}z}}z^{N'-N}. $$
Here $N,M,N',M'\in\Bbb Z_+$, $\alpha_j,\alpha_j',\beta_j,\beta_j'\geqslant 0$; if $\beta=0$, then the factor $\sin{\beta z}$ is replaced by $z$; if $N,M,N'$, or $M'$ equals zero, then the corresponding factors are absent. A criterion of logarithmic absolute monotonicity for $f$ is obtained.
We give some applications of absolute monotonicity to sharp inequalities for derivatives and differences of trigonometric polynomials and entire functions of exponential type.

Key words and phrases: absolutely monotone functions, Bernstein inequality.

UDC: 517.5

Received: 14.06.2021



© Steklov Math. Inst. of RAS, 2025