Re: decimation
The general definition of decimation is decreasing the sampling frequency of the signal. These operation is usually done in the integer amount of times. Matlab has the special function decimate(), available in Command Window for getting further instructions of its use.
So it won't take much of your time, if you open Matlab and search this function in it's vast and rich Help. No doubt, you'll find many useful facts on your question.
With respect,
Dmitrij