# Hardy transform

From Encyclopedia of Mathematics

The integral transform

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

where

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

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

$$f(t)=\int\limits_0^\infty\Phi(tx)xF(x)dx,$$

where

$$\Phi(x)=\sum_{n=0}^\infty\frac{(-1)^n(x/2)^{\nu+2p+2n}}{\Gamma(p+n+1)\Gamma(\nu+p+n+1)}.$$

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

#### References

[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: http://www.encyclopediaofmath.org/index.php?title=Hardy_transform&oldid=32672

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