AFL Library

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Details:

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Description:

Uses Peak() & Trough() to determine 3 pivot points to use in plotting Andrews Pitchfork. Params: zig pct for peak and trough, look back before using peak/trough, no. of bars to extend pitchfork, shift to move pitchfork up/down, angle limit to filter out steep pitchforks, background and pitchfork color. This version replaces an earlier version that had some unused variables and lacked the angle limit and color params.

Formula:

// Andrews Pitchfork V3.1
// Use Peak() & Trough() to get peaks & troughs.
// This version deals with adjacent peaks and adjacent
// troughs, i.e. two peaks without an intervening trough or vice-versa.
// It goes backwards from the selected bar until it has a set of 
// peak,trough,peak or trough,peak,trough points to use for calulating
// the pitchfork.  When 2 or more peaks or 2 or more troughs are adjacent
// it only uses the last one, i.e. the rightmost one, of the series.
//
// Compared to V3.0 this version looks at the angle described by the handle
// line's logs.  It will look skip pitchforks that have angles beyond the
// angle threshhold limit param.
//
// This version plots the trendlines as exponential curves that plot as
// straight lines on an semilog chart.
//
// 07/22/2005 By Bob Johnson with invaluable help from Graham Kavanagh getting
// me pointed in the right direction on the exponential equation logic.

SetBarsRequired( 999999,999999);

bi=BarIndex();
sbi=SelectedValue(bi);

// How many bars to wait before believing the pivot.
Lookbk=Param("LookBack",5,1,200,1);

// Pct threshhold for peak() & trough()
Zigpct=Param("Zigpct",3.0,1.0,30.0,0.1,0);

// How many bars to extend the pitchfork past the selected bar.
xtsn=Param("Extension",62,1,200,1);

// Shift to move pitchfork up/down from original position one penny at time.
shift=Param("Shift",0,-2000,2000,0.01);

// Filter out cases when the angle of the median lines is too extreme,
// The loop will continue until it finds a pitchfork whose slope falls 
// between +- the Angle Limit.  Setting the angle limit to 90 effectively
// turns it off.
alimit=Param("Angle Limit",40,1,90,1);

// bkgrndcolor should match your background color.  It's used to mask the 
// parts of the pitchfork arrays outside the calculated pitchfork from view.
bkgrndcolor=ParamColor("Background Color",colorLightGrey);
pitchforkcolor=ParamColor("Pitchfork Color",colorRed);

// The peak/trough lines will be used to determine the y coordinates
// of the pitchfork's 3 determining points.

pline1=Peak(H,Zigpct,1);
tline1=Trough(L,Zigpct,1);

// Identify the pivots.

pzag1=pline1 != Ref(pline1,-1);
tzag1=tline1 != Ref(tline1,-1);

// Get the x,y coordinates of the pivots skipping adjacent
// peaks and troughs.  Go backwards from the current bar minus the lookback.

// These will hold the x,y coordinates of the pivot points in arrays at the
// sbi index.

zagx1=0;
zagx2=0;
zagx3=0;
zagy1=0;
zagy2=0;
zagy3=0;

for ( i = sbi - Lookbk, zagfnd = 0, pzagfnd = 0, tzagfnd = 0 ; i >= 0 && zagfnd
<= 3; i-- ) {
    if ( pzag1[i] || tzag1[i] ) {
        if ( pzag1[i] && NOT pzagfnd ) {
             zagfnd=zagfnd+1;
             pzagfnd=1;
             tzagfnd=0;
             if ( zagfnd == 1 ) {
                 zagx1[sbi]=i;
                 zagy1[sbi]=pline1[i];
             } else if (zagfnd == 2) {
                 zagx2[sbi]=i;
                 zagy2[sbi]=pline1[i];
             } else if (zagfnd == 3) {
                 zagx3[sbi]=i;
                 zagy3[sbi]=pline1[i];
             }
        } else if ( tzag1[i] && NOT tzagfnd ) {
             zagfnd=zagfnd+1;
             tzagfnd=1;
             pzagfnd=0;
             if ( zagfnd == 1 ) {
                 zagx1[sbi]=i;
                 zagy1[sbi]=tline1[i];
             } else if (zagfnd == 2) {
                 zagx2[sbi]=i;
                 zagy2[sbi]=tline1[i];
             } else if (zagfnd == 3) {
                 zagx3[sbi]=i;
                 zagy3[sbi]=tline1[i];
             }
        }
    }

    if ( zagfnd == 3 ) {  // Got 3 candidate peak/trough points

        echng=0;
        midx=0;
        midy=0;
        Handle=0;
        Top=0;
        Bot=0;

        // Determine Midpoint between the rightmost 2 pivots and the slope from
the
        // leftmost pivot to the midpoint.

        Midx[sbi]=zagx2[sbi] + (zagx1[sbi]-zagx2[sbi]) / 2;
        Midy[sbi]=exp( log(zagy1[sbi]) - ( log(zagy1[sbi])-log(zagy2[sbi]) ) /
2);
        echng=(log(midy[sbi])-log(zagy3[sbi]))/(midx[sbi]-zagx3[sbi]);

        // Apply the Angle Limit filter

        angle_rad = atan(echng);//radians
        angle_deg = 100 * angle_rad * 180/3.1416;//degrees

        if ( angle_deg < -alimit || angle_deg > alimit ) { // Too steep, reset
the search
                                                           // to begin from the
2nd pivot found
            if ( tzagfnd == 1 ) {  // was tr,pk,tr so switch to pk,tr,pk
                tzagfnd = 0;
                pzagfnd = 1;
                zagfnd = 1;
                zagx1[sbi]=zagx2[sbi];
                zagy1[sbi]=zagy2[sbi];
                i = zagx1[sbi];
                zagx2=0;
                zagx3=0;
                zagy2=0;
                zagy3=0;
            } else {  // was pk,tr,pk so switch to tr,pk,tr
                tzagfnd = 1;
                pzagfnd = 0;
                zagfnd = 1;
                zagx1[sbi]=zagx2[sbi];
                zagy1[sbi]=zagy2[sbi];
                i = zagx1[sbi];
                zagx2=0;
                zagx3=0;
                zagy2=0;
                zagy3=0;
            }        }
    }
}

// Calculate the Pitchfork itself

// Handle first

for ( j=zagx3[sbi],n=0 ; j < Min(sbi+xtsn,BarCount) ; j++,n++ ) {
   Handle[j]=exp(log(zagy3[sbi]) + n*echng) + shift;
}

// High & low median lines.

if ( zagy2[sbi] > zagy1[sbi] ) {  // Which one is top?
   for ( j=zagx2[sbi],n=0 ; j < Min(sbi+xtsn,BarCount) ; j++,n++ ) {
      top[j]=exp(log(zagy2[sbi]) + n*echng) + shift;
   }
   for ( j=zagx1[sbi],n=0 ; j < Min(sbi+xtsn,BarCount) ; j++,n++ ) {
      bot[j]=exp(log(zagy1[sbi]) + n*echng) + shift;
   }
} else {
   for ( j=zagx2[sbi],n=0 ; j < Min(sbi+xtsn,BarCount) ; j++,n++ ) {
      bot[j]=exp(log(zagy2[sbi]) + n*echng) + shift;
   }
   for ( j=zagx1[sbi],n=0 ; j < Min(sbi+xtsn,BarCount) ; j++,n++ ) {
      top[j]=exp(log(zagy1[sbi]) + n*echng) + shift;
   }
}

Hcolor=IIf(Handle==0,bkgrndcolor,IIf(Ref(handle,-1)== 0 AND handle != 0,
bkgrndcolor,pitchforkcolor));
Tcolor=IIf(Top==0,bkgrndcolor,IIf(Ref(top,-1)== 0 AND top != 0,
bkgrndcolor,pitchforkcolor));
Bcolor=IIf(Bot==0,bkgrndcolor,IIf(Ref(bot,-1)== 0 AND bot != 0,
bkgrndcolor,pitchforkcolor));
Plot(Handle,"\nAndrews: pct="+Zigpct+" lookback="+lookbk+" shift="+shift+"
alimit="+alimit+" Angle="+angle_deg+"
Handle",Hcolor,styleLine+styleDashed+styleNoRescale);
Plot(Bot,"MLL",Bcolor,styleLine+styleDashed+styleNoRescale);
Plot(Top,"MLH",Tcolor,styleLine+styleDashed+styleNoRescale);

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