I'd like to write this function (LowPass) in Mql4 in order to plot on MT4 but I found that I don't understand the "series" function.

var smoothF(int period) { return 2./(period+1); }

var LowPass(var *Data,int Period)
{
var* LP = series(*Data,3);
var a = smoothF(Period);
var a2 = a*a;
return LP[0] = (a-0.25*a2)*Data[0]
+ 0.5*a2*Data[1]
- (a-0.75*a2)*Data[2]
+ 2*(1.-a)*LP[1]
- (1.-a)*(1.-a)*LP[2];
}

What does exactly do this line ?
var* LP = series(*Data,3);
LP is a 3 element array filled with "what" of "*Data" ?
I thought that was filled with the first 3 elements of "*Data" but it seems to be that it's not true.

Could someone help me with this ?
Thanks.