Bollinger Band Top Bottom Accurate Signals - Amibroker AFL Code

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SetChartOptions(0,chartShowArrows|chartShowDates);
_N(Title = StrFormat("{{NAME}} - {{INTERVAL}} {{DATE}} Open %g, Hi %g, Lo %g, Close %g (%.1f%%) {{VALUES}}", O, H, L, C, SelectedValue( ROC( C, 1 ) ) ));
Plot( C, "Close", ParamColor("Color", colorBlack ), styleNoTitle | ParamStyle("Style") | GetPriceStyle() ); 
_SECTION_END();

_SECTION_BEGIN("Kolkata Meet - Bands");
//..........................................................................
 
a = Param("Angle Degrees",30,15,90,15);
n = Param("Slope_Bars",5,10,50,1);

a    = (22 / 7) * (a / 180);

Num = NumL = NumH = 0;
Den = 0;

for (i = 1;i < n+1;i++)
{
 Num  = Num  + sin(i * a) * Ref(C,-i-1);
 NumL = NumL + sin(i * a) * Ref(L,-i-1);
 NumH = NumH + sin(i * a) * Ref(H,-i-1);
 Den = Den + sin(i * a);
}

j  = Num/Den;
jL = NumL/Den;
jH = NumH/Den;

Plot(j, "Slope", IIf(j > Ref(j,-1), colorBlueGrey,colorLime), styleThick | styleDashed);
Plot(jL, "LB", colorLime,styleThick | styleDashed);
Plot(jH, "UB", colorBlueGrey,styleThick | styleDashed);

_SECTION_END();

_SECTION_BEGIN("Signal 04");
Buy  = C > jH;
Sell = C < jL;

Buy  = ExRem(Buy,Sell);
Sell = ExRem(Sell,Buy);

Short = Sell;
Cover = Buy;

Short = ExRem(Short,Cover);
Cover = ExRem(Cover,Short);
_SECTION_END();


_SECTION_BEGIN("Plot Arrows");
//Position size fixed 100 units
SetPositionSize(100,4);
SetTradeDelays(1,1,1,1);


PlotShapes(shapeUpArrow * Buy, colorBlue,0, L,-20);
PlotShapes(shapeDownArrow * Short, colorRed,0, H, -20);

_SECTION_BEGIN("Bollinger Bands");
P = ParamField("Price field",-1);
Periods = Param("Periods", 15, 2, 100, 1 );
Width = Param("Width", 2, 0, 10, 0.05 );
Color = ParamColor("Color", colorCycle );
Style = ParamStyle("Style");
Plot( BBandTop( P, Periods, Width ), "BBTop" + _PARAM_VALUES(), Color, Style ); 
Plot( BBandBot( P, Periods, Width ), "BBBot" + _PARAM_VALUES(), Color, Style ); 
_SECTION_END();