TOPICS
Search

Cylinder Function


CylinderFunction

The cylinder function is defined as

 C(x,y)={1   for sqrt(x^2+y^2)<=a; 0   for sqrt(x^2+y^2)>a.
(1)

The Bessel functions are sometimes also called cylinder functions.

To find the Fourier transform of the cylinder function, let

k_x=kcosalpha
(2)
k_y=ksinalpha
(3)

and

x=rcostheta
(4)
y=rsintheta.
(5)

Then

F(k,a)=F_(x,y)[C(x,y)](k,a)
(6)
=int_0^(2pi)int_0^ae^(i(krcosalphacostheta+krsinalphasintheta))rdrdtheta
(7)
=int_0^(2pi)int_0^ae^(ikrcos(theta-alpha))rdrdtheta.
(8)

Let b=theta-alpha, so db=dtheta. Then

F(k,a)=int_(-alpha)^(2pi-alpha)int_0^ae^(ikrcosb)rdrdb
(9)
=int_0^(2pi)int_0^ae^(ikrcosb)rdrdb
(10)
=2piint_0^aJ_0(kr)rdr
(11)
=(2pia)/kJ_1(ka)
(12)
=2pia^2(J_1(ka))/(ka).
(13)

where J_n(x) is a Bessel function of the first kind.

As defined by Watson (1966), a "cylinder function" is any function which satisfies the recurrence relations

 C_(nu-1)(z)+C_(nu+1)(z)=(2nu)/zC_nu(z)
(14)
 C_(nu-1)(z)-C_(nu+1)(z)=2C_nu^'(z).
(15)

This class of functions can be expressed in terms of Bessel functions.


See also

Bessel Function of the First Kind, Cylindrical Function, Hemispherical Function, Parabolic Cylinder Function

Explore with Wolfram|Alpha

WolframAlpha

More things to try:

References

Watson, G. N. A Treatise on the Theory of Bessel Functions, 2nd ed. Cambridge, England: Cambridge University Press, 1966.

Referenced on Wolfram|Alpha

Cylinder Function

Cite this as:

Weisstein, Eric W. "Cylinder Function." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CylinderFunction.html

Subject classifications