# The Excel BESSELK Function

## Basic Description

The Excel Besselk function calculates the modified Bessel functions, Kn(x), which are also known as the hyperbolic Bessel Functions. These are the equivalent of the Bessel functions, evaluated for purely imaginary arguments.

The syntax of the function is :

BESSELK( x, n )

where the function arguments are:

 x - The value at which the function is to be evaluated n - A positive integer, denoting the order of the modified Bessel function(If the supplied value of n is a decimal, it is truncated to an integer by Excel)

## Besselk Function Example

Order 1 Modified Bessel Function, Kn(x)

The above chart on the right shows the modified Bessel function, Kn(x), of order 1.

If you want to calculate the value of this function at x = 0.05, this can be done using the following formula:

=BESSELK( 0.05, 1 )

which gives the result 19.90967433.

Further examples of the Excel Besselk function can be found on the Microsoft Office website.

## Besselk Function Errors

If you get an error from the Excel Besselk function this is likely to be one of the following :

Common Errors
 #NUM! - Occurs if either:the supplied value of x is ≤ 0the supplied value of n is < 0 #VALUE! - Occurs if any of the supplied arguments are non-numeric #NAME? - Occurs when Analysis ToolPak add-in is not enabled in your Excel. You will need to enable the add-in if you want to use the Excel engineering functions.