KELVIN_KER0 Function

Evaluates the Kelvin function of the second kind, ker, of order zero.

Usage

result = KELVIN_KER0(x)

Input Parameters

x—Argument for which the function value is desired.

Returned Value

result—The value of the Kelvin function of the second kind, ker, of order zero evaluated at x.

Input Keywords

Double—If present and nonzero, double precision is used.

Derivative—If present and nonzero, then the derivative of the Kelvin function of the second kind, ker, of order zero evaluated at x is computed.

Discussion

The modified Kelvin function ker₀(x) is defined to be . The Bessel function K₀(x) is defined:

 

If the keyword Derivative is set, the function ker₀'(x) is defined to be:

 

If x < 0, NaN (Not a Number) is returned. If x ³ 119, then zero is returned.

The function KELVIN_KER0 is based on the work of Burgoyne (1963).

Example

In this example, ker₀(0.4) and ker₀'(0.6) are evaluated.

PRINT, KELVIN_KER0(0.4)

; PV-WAVE prints: 1.06262

PRINT, KELVIN_KER0(0.6, /DERIVATIVE)

; PV-WAVE prints: -1.45654