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I suspect the answer lies in the "Operator Precedence" in conjunction with
the PREV function. If Operator Precedence is not involved, you must
recognize that the PREV constant cannot be treated in a conventional
algebraic context like any other constant or variable. That is, you cannot
multiply or divide through an expression to eliminate a PREV. For instance
(PREV(C+PREV) is not the same as C*PREV + PREV^2 or (Pr+PREV-PREV) is not
the same as Pr.
Jim Barone
----- Original Message -----
From: C.S. <csaxe@xxxxxxxxxxx>
To: MetaStock List <metastock@xxxxxxxxxxxxx>
Sent: Friday, March 23, 2001 1:11 PM
Subject: More PREV Stuff
> 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
>
>
>
>
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