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The Excel BESSELJ Function
Basic Description
The Excel Besselj function returns the Bessel function, J_{n}(x), for a specified order and a given value of x.
The syntax of the function is :
BESSELJ( x, n )
where the function arguments are:
x    The value at which the function is to be evaluated 
n    The order of the Bessel function (must be a positive integer) (If the supplied value of n is a decimal, Excel truncates this value to an integer) 
Besselj Function Example
Order 1, 2 & 3 Bessel Functions, J
_{n}(x)
The above chart on the right shows the Bessel functions, J_{n}(x), of order 1, 2 and 3.
The value of any of these functions at a given value of x, can be evaluated using the Excel Besselj function.
For example, the order 1 Bessel function, at x=2.5 is calculated by the following:
=BESSELJ( 2.5, 1 )
This gives the result 0.497094103.
Further examples of the Excel Besselj function can be found on the Microsoft Office website.
Besselj Function Errors
If you get an error from the Excel Besselj function, this is likely to be one of the following :
Common Errors
#NUM!    Occurs if the supplied value of n is < 0 
#VALUE!    Occurs if any of the supplied arguments are nonnumeric 
#NAME?    Occurs when Analysis ToolPak addin is not enabled in your Excel. You will need to enable the addin if you want to use the Excel engineering functions.
+ Show How to Do This in Excel 2003:
 From the Tools dropdown menu, select the option AddIns ...
 An 'AddIns' window will pop up. From this, select the option Analysis ToolPak and click OK
+ Show How to Do This in Excel 2007:
 Click the Microsoft button on the top left of your spreadsheet and select
the Excel Options button
 From the menu on the left hand side, select AddIns
 In the 'Manage:' box, select Excel Addins and click Go...
 An 'AddIns' window will pop up. From this, select the option Analysis ToolPak and click OK
+ Show How to Do This in Excel 2010 or Excel 2013:
 Click the File tab (top left of your spreadsheet) and select Options
 From the menu on the left hand side, select AddIns
 If the window that pops up doesn't show the 'Addins' list, use the 'Manage:'
dropdown menu (at the bottom of the window) to select Excel Addins. Click Go...
 From the 'AddIns' window, select the option Analysis ToolPak and click OK
