More PREV Stuff

["C.S." <csaxe@xxxxxxxxxxx>]

Just when I thought that I was beginning to figure out Metastock formula
language, the following was listed in Apr 01 TASC Traders' Tips as the
solution to Ehler's nonlinear filter article. The first one is easy to
figure out from the article.

{Ehlers Filters}
ti:=15;
pr:=MP();
coef:=Abs(pr-Ref(pr,-5));
Sum(coef*pr,ti)/Sum(coef,ti)


This one works, but has me stumped as to how it works according to the
article. You really have to read the article to understand what is being
calculated here.

{Distant Coefficient Ehlers Filter}
ti:=15;
pr:=MP();
coef:=Sum(Power(Ref(LastValue(pr+PREV-PREV)-pr,-1),2),ti);
Sum(coef*pr,ti)/Sum(coef,ti)

The two PREV would appear to be just adding a number and then subtracting a
number, leaving "pr" but that isn't the case. The formulas were written by
Cheryl Abram of Equis. It would be nice if someone at Equis would consider
having her give a us a quick class on how this works and other formula
construction tips.

I came up with:

ti:=15;
pr:=MP();
coef:=Sum(Power(LastValue(pr)-Ref(pr,-1),2),ti);
Sum(coef*pr,ti)/Sum(coef,ti)

This works too, but doesn't follow rapid price changes as quickly as
Cheryl's formula.

Any ideas on how the two PREV act together?

-Corey