How to call a controller from another controller ?

[eluser]Vivigeos[/eluser]
Hi everyone,
Here's my problem... I would like to create a controller which could call other controllers.
For example, I've a controller called "index" used to provide the index page (a blog page here) and I would like too call the "category" controller and one of its methods which displays a list of the categories in a view. Then I would like to add this category view to my index view.
Is it possible ?

Thanks for your time.