Hardy transform

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The integral transform

$$F(x)=\int\limits_0^\infty C_\nu(xt)tf(t)dt,$$


$$C_\nu(z)=\cos p\pi J_\nu(z)+\sin p\pi Y_\nu(z),$$

and $J_\nu(z)$ and $Y_\nu(z)$ are the Bessel functions of the first and second kinds, respectively. For $p=0$ the Hardy transform coincides with one of the forms of the Hankel transform, and for $p=1/2$ with the $Y$-transform. The Hardy transform was proposed by G.H. Hardy in [1].

The inversion formula is




The Hardy transform is also defined for certain classes of generalized functions.


[1] G.H. Hardy, "Some formulae in the theory of Bessel functions" Proc. London. Math. Soc. (2) , 23 (1925) pp. 61–63
[2] Y.A. Brychkov, A.P. Prudnikov, "Integral transforms of generalized functions" , Gordon & Breach (1989) (Translated from Russian)
How to Cite This Entry:
Hardy transform. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by Yu.A. BrychkovA.P. Prudnikov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article