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GENERALIZED LOGARITHMIC DERIVATIVE ESTIMATES OF GOL'DBERG–GRINSHTEIN TYPE

Published online by Cambridge University Press:  23 December 2003

J. HEITTOKANGAS
Affiliation:
University of Joensuu, Department of Mathematics, P. O. Box 111, FIN-80101 Joensuu, Finland, rattya@cc.joensuu.fi (Current address) University of Illinois at Urbana-Champaign, Department of Mathematics, 1409 W. Green Street, Urbana, IL 61801, USAjanne@math.uiuc.edu
R. KORHONEN
Affiliation:
University of Joensuu, Department of Mathematics, P. O. Box 111, FIN-80101 Joensuu, Finland, rattya@cc.joensuu.fi (Current address) Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, LE11 3TU r.j.korhonen@lboro.ac.uk
J. RÄTTYÄ
Affiliation:
University of Joensuu, Department of Mathematics, P. O. Box 111, FIN-80101 Joensuu, Finland, rattya@cc.joensuu.fi
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Abstract

For $f$ meromorphic in the complex plane and $\varphi$ meromorphic in the unit disc, sharp upper bounds are obtained for $$m\left(r,\frac{f^{(k)}}{f^{(j)}}\right)=\frac{1}{2\pi}\int_0^{2\pi} \log^{+}\left|\frac{f^{(k)}(re^{i\theta})}{f^{(j)}(re^{i\theta})}\right |\, d\theta,\qquad r<\infty,$$ and $$m\left(r,\frac{\vp^{(k)}}{\vp^{(j)}}\right)=\frac{1}{2\pi}\int_0^{2\pi} \log^{+}\left|\frac{\vp^{(k)}(re^{i\theta})}{\vp^{(j)}(re^{i\theta})}\right |\, d\theta,\qquad r<1,$$ where $k$ and $j$ are integers satisfying $k>j\geq 0$. The results generalize the logarithmic derivative estimate due to Gol'dberg and Grinshtein to derivatives of higher order.

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Papers
Copyright
© The London Mathematical Society 2004

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