Hadamard three-circle theorem
Let be a holomorphic function on the annulus
The conclusion of the theorem can be restated as
for any three concentric circles of radii
A statement and proof for the theorem was given by J.E. Littlewood in 1912, but he attributes it to no one in particular, stating it as a known theorem. Harald Bohr and Edmund Landau attribute the theorem to Jacques Hadamard, writing in 1896; Hadamard published no proof.
The three circles theorem follows from the fact that for any real a, the function Re log(zaf(z)) is harmonic between two circles, and therefore takes its maximum value on one of the circles. The theorem follows by choosing the constant a so that this harmonic function has the same maximum value on both circles.
The theorem can also be deduced directly from Hadamard's three-lines theorem.
- Maximum principle
- Logarithmically convex function
- Hardy's theorem
- Hadamard three-lines theorem
- Borel–Carathéodory theorem
- Phragmén–Lindelöf principle
- Edwards, H.M. (1974), Riemann's Zeta Function, Dover Publications, ISBN 0-486-41740-9
- Littlewood, J. E. (1912), "Quelques consequences de l'hypothese que la function ζ(s) de Riemann n'a pas de zeros dans le demi-plan Re(s) > 1/2.", Les Comptes rendus de l'Académie des sciences, 154: 263–266
- E. C. Titchmarsh, The theory of the Riemann Zeta-Function, (1951) Oxford at the Clarendon Press, Oxford. (See chapter 14)
- Ullrich, David C. (2008), Complex made simple, Graduate Studies in Mathematics, 97, American Mathematical Society, pp. 386–387, ISBN 0821844792