/* Regression Analysis - Graph a Straight Line
** AFL Implementation by Frank Snay
** The Program is designed to graph a user defined length, straight regression 
** analysis line.  Percentage lines, also user defined, are drawn above and
** below the regression analysis line.  
** A user defined "DaysBack" draws the line back (think AFL code ref() ) from 
** the current end of the data for those who want to see a graphed, historical
** line from previous days.  Setting "DaysBack" to zero ends the graph on the
** current last database day.
** Candlestick code displayed, with the green box with white fill being a day where
** the close exceeds the open, and a red box with black fill being a day where the
** open exceeds the close. (Tj - any way to make the fill the same color as the boxes?)
** Use Automatic scaling, Grid: Middle + ShowDates 
** THE FOLLOWING ARE USER INPUTS FOR THE DESIRED RESULTS:
** User Input - Number of Days for Regression Analysis Line Study  */
periods =63;
/*  User Input - Upper and Lower Line seperation in percentage */
Percent = 10;
/* User Input - Number of days BACK for Historical Test */
DaysBack = 0; //Keep at 0 for current regression analysis line

/*  Compute the number of bars in datafile  */
RABars = 0; //initialize
TotalBars = cum(1); //how many bars in database
FinalBar = lastvalue(TotalBars);//number value of last bar
EndDay = FinalBar - DaysBack;//for other than 0 DaysBack
StartDay = EndDay - periods+1;//starting point for line
Master1 = iif(TotalBars >= StartDay and TotalBars <= EndDay,1,0);//defined period
RABars = iif(Master1,ref(RABars,-1)+1,0); // daily counter in defined period
RABarKntr = iif(Master1,sum(RABars,periods),0); //Sum of daily counts

/*  Regression Analysis Computations  */
TempMeanX = iif(RABarKntr == periods,sum(RABarKntr,periods),0);  // Sum of individual day counters
MeanX1 = hhv(TempMeanX,TotalBars)/periods;  //  Final number divided by number of days
MeanX = lastvalue(MeanX1); 
TempMeanY =  iif(RABarKntr == periods, sum(c,periods),0);
MeanY1 = hhv(TempMeanY,TotalBars)/periods ;  //  Final sum  divided by number of days
MeanY = lastvalue(MeanY1);  
Slope1 = iif(TotalBars == EndDay,linregslope(c,periods),0);
Slope2 = iif(hhv(Slope1,FinalBar)>= 0,hhv(slope1,FinalBar),llv(Slope1,FinalBar));
slope = lastvalue(Slope2);
Intercept = MeanY -Slope * MeanX;

/*  Linear Regression Line = Intercept plus the Slope times RABarKntr  */
LRLine = Intercept + Slope * RABarKntr; 

/*  Convert Percent to decimal */
Percent1 = Percent/100;

/* Add half to LRLine to get upper, subtract half to get lower */
UpperLRLine = LRLine * (1+(Percent1)/2);
LowerLRLine = LRLine * (1-(Percent1)/2);

/*  Following 3 lines - graph ONLY days in the period */
UpperLRLine = iif(RABarKntr >= 1,LRLine*(1+Percent1/2),-1e10);
LowerLRLine = iif(RABarKntr>= 1, LRLine *(1-Percent1/2),-1e10);
LRLine = iif(RABarKntr >= 1, LRLine,-1e10);

/*  Graph the output  */
// candlestick chart drawn here
maxgraph=4;
graph0 = close;
graph0style = 64;
graph0barcolor = iif(c>=o,5,4); //Green or Red candlestick graphs
graph0color =2;
graph1style = graph2style = graph3style = 1;
graph1color = graph2color = graph3color  = 7;
graph1 =LRLine;
graph2 =UpperLRLine;
graph3 =LowerLRLine;