[amibroker] Please help me with this regression channel code

["tradinghumble" <sharp2be@xxxxxxxxx>]

Hi, the code below is part of an afl written by Patrick Hargus and is
on the AFL Library:
== partial code
P = ParamField("Price field",-1);
Daysback = Param("Period for Liner Regression Line",21,1,240,1);
shift = Param("Look back period",0,0,240,1); 

//  =============================== Math Formula
x = Cum(1);
lastx = LastValue( x ) - shift; 
aa = LastValue( Ref(LinRegIntercept( p, Daysback), -shift) ); 
bb = LastValue( Ref(LinRegSlope( p, Daysback ), -shift) ); 
y = Aa + bb * ( x - (Lastx - DaysBack +1 ) ); 

LRColor = ParamColor("LR Color", colorCycle ); 
LRStyle = ParamStyle("LR Style");
LRLine =  IIf( x > (lastx - Daysback) AND BarIndex() < Lastx, y, Null );
Plot( LRLine , "LinReg", LRCOLOR, LRSTYLE ); //  styleDots ); 

// ==========================  Plot 1st SD Channel
SDP = Param("Standard Deviation", 1.5, 0, 6, 0.1);
SD = SDP/2;

width = LastValue( Ref(SD*StDev(p, Daysback),-shift) );   // THIS IS
WHERE THE
WIDTH OF THE CHANELS IS SET  
SDU = IIf( x > (lastx - Daysback) AND BarIndex() < Lastx, y+width ,
Null ) ;
SDL = IIf( x > (lastx - Daysback) AND BarIndex() < Lastx, y-width ,
Null ) ;

SDColor = ParamColor("SD Color", colorCycle ); 
SDStyle = ParamStyle("SD Style");

Plot( SDU , "Upper Lin Reg", SDColor,SDStyle ); 
Plot( SDL , "Lower Lin Reg", SDColor,SDStyle ); 


======================
I was wondering if anyone could help to plot the value of the last
lower regression line SDL as a band instead of a channel... 

I know there's the "shift" parameter but I'm just not sure how to make
it change for each bar.

Thanks a lot.




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