Access global function in Model

Hi Everyone,
Can anyone pls tell me how to access a Common Function in
"application.rb" controller in a Model.
For example, i am having a function to find the Factorial of a number.
Where should i place this function, so that i can access through out the
application (in all controllers and models)? For now i have placed in
"application.rb" controller.

If you need it in both controllers AND models then you probably want
to wrap it in a plain Ruby class and include it in your models.

For example...

class MathLib
  def self.factorial(n)

Then you can call MathLib.factorial n anywhere in your code.

If this is code that you'd like to carry from project to project you
might also consider making this a module, rather than a class, so that
you can include the module in the classes that need to make use of the