Paul,
I believe we can indeed give you some answers.
A little history behind the indicator. Originally it was part of
some work done by Thomas Stridsman for Futures Magazine...I believe
that was in 1998. It 2004 it appeared in Traders Mag. Here is a
summary:
"Dynamic Breakout System" (Trading System Lab, Feb. 2003)
Author: Thomas Stridsman
Summary: This system enters a long (short) trade if the last closing
price is above (below) the highest high (lowest low) of the lookback
period. The lookback period changes based on market volatility.
The Tradestation folks have written a very good discussion(PDF) on
the indicator which I will upload into our files section for you.
Years ago, before this forum and many others were around the folks
at Equis hosted a forum that I was simply known as Metastock. A
fellow by the name of Walter Lake introduced Stridsman's work to the
group back in '98. There was also a bit of discussion about the use
of +prev-prev. Turns out that it is the key to making the
indicator "dynamic" or what we call variable in today's terminology.
Luckily we can still go back and review some of those earlier posts
and the site listed below will get you there.
http://www.purebytes.com/cgi-local/swish/swish-cgi.pl
Search for DBS
Metastock
1998
This will pull up all the old discussions about the system.
Also
http://www.purebytes.com/archives/metastock/1998/msg06413.html
>From Walter:
-----snip-------
The "+Prev-Prev" comments in the article should be researched when
using "DBS Lookback" in other Metastock indicators.
Here's one writer's experience ... "I tested both versions on several
indices and found them to be different too:
This +PREV-PREV causes a shift to the left of the indicator, a trick
to center an indicator?"
"after some testing, I found that without +PREV-PREV LastValue will
deliver a constant value (the last value for LookBack in Your chart).
So in writing Tema(C,LastValue(Fml("LookBack"))) You get a TEMA with
a constant period, as required by Metastock.
By using Tema(C,LastValue(Fml("LookBack")+PREV-PREV))
You get what You want, a TEMA with a variable period. Nice trick!"
Walter
----snip-----
Realize that back then we didn't have DLL's so our only recourse was
to get a little creative with indicators. Today we have DLL's and it
is for just such a purpose that they should be used.
The answer then to removing the prevs is to use a DLL.
Lnc:=Ref(HHV(H,LastValue(Fml("DBS-LookBack")+PREV-PREV)),-1);
using the equis forum DLL available in our files, EquisForum, or
Traders Consortium the formula would then become:
LNC:=Ref(ExtFml("ForumDLL.VarHHV",H,Fml("DBS-LookBack")),-1);
You will notice that LastValue is no longer used as well.
That takes care of the majority of prev statements and should speed
up your work quite a bit. If you would like I will continue to look
at DBS-Lookback indicator and see if that prev can be removed as
well if you like.
After reading the Tradestation PDF entitled Dynamic Breakout II
Strategy I think you will find that this system certainly has some
merit although it does need some work.
Glad we could help,
Preston
--- In equismetastock@xxxxxxxxxxxxxxx,
ppappppapp <no_reply@xxx>
wrote:
>
> Greetings all,
>
> A 'little bird' suggested that I should post my querry here and
> hopefully someone might offer some advice.
>
> O.k. here goes;
>
> The following indicators are based on the Dynamic Breakout system
> (DBS) as found in Thomas Stridsman's book "Trading systems that
work"
>
> It's simply a variation on the Turtle channel breakout method
where
> you buy a breakout above the highest high of `x' number of days
ago.
> (i.e. a HHV channel)
> This DBS system varies the channel width dynamically according to
> price volatility (as measured by standard deviation)
>
> The following indicator finds the VALUE of the varying channel
width
> (in this case the HHV channel will vary between 20 and 100 bars
ago)
> and is then referenced into the second indicator
>
> ******************************
>
> {DBS-Lookback}
>
> {-----User Inputs-----}
>
> VolPer:=Input("Enter StdDev periods",1,100,30);
> LBmin:=Input("Enter Min. lookback periods for entry",5,100,20);
> LBmax:=Input("Enter Max. lookback periods for entry",20,200,100);
>
>
> HV:= Stdev(C, VolPer);
> YestHV := Ref(HV, -1);
> DeltaHV := 1+((HV-YestHV)/HV);
> If(Cum(1)=1,LBmin,Min(Max(PREV*DeltaHV,LBmin),LBmax));
>
> ********************************
>
> This following second indicator then references the above first
> indicator to plot entry and exit signals
> (i.e. not `clean' signals but ALL valid signals where they occur)
>
> ********************************
>
> {DBS-Lsigs}
>
> {Dynamic Breakout system - Long signals}
>
> { User inputs }
> Mess1:=Input("Change defaults in DBS-Lookback Indicator",0,0,0);
>
> {Long entry & Long exit Channel}
> Lnc:=Ref(HHV(H,LastValue(Fml("DBS-LookBack")+PREV-PREV)),-1);
>
> Lxc:=Ref(LLV(L,LastValue(Fml("DBS-LookBack")+PREV-PREV)),-1);
>
> { Entry/Exit Long breakouts }
> entry:=H>Lnc;
> exit:= L<Lxc;
>
> entry;
> -exit
>
> *******************************
>
> o.k., now for the question;
>
> You will note from the above, the use of one(1) PREV command in
the
> first indicator and four(4) PREV commands in the second indicator
(as
> well as the PREV command associated with the referenced formula
> within this indicator)
>
> Although the indicators work fine and dandy, they take a long,
Long,
> L—--O--—N—--G time to plot on screen. Obviously due to
the large
> amount of computer resource demanded by the PREV command.
> If I attempt to run an exploration on numerous stocks/futures
using
> these indicators, I generally have to do it at night just before
bed.
> The results are available for me in the morning. (lucky I sleep
for
> 8+ hours)
>
> Is there anything I can do to the indicator code to speed up the
> execution?
> Or is this simply a Metastock limitation that I will have to live
> with?
> In short how can i replace the PREV commands?
>
> Any tips would be much appreciated.
>
>
> Thanks kindly,
>
> Paul
>
