Need help understanding what this filter does

Hi All,

I'm in the process of expanding a Matlab application that someone else has written (don't worry, I have their permission). However, I'm stuck. I can't work out what the following filter is doing?

Fil = filter(1-am, [1 -am], daten, init)

Some more info, am = 0.8, daten = a range of numbers in an array, and init = 0.027.

I've scoured the help docs but am none the wiser, so help is greatly appreciated.

Answer 1

[Honglei Chen]

It is just an auto regressive filter, in your case, your filter coefficients are

b = 0.2
a = [1 -0.8]

So if you write it into difference equation, it is basically

y[n] = 0.8*y[n-1] + 0.2*x[n]

i.e., the output is determined by both the previous output and the current input, and the previous output is weighted more.