super bandpass filter by John Ehlers

//@version=2
//plot by marco
//The Super Passband Filter by John Ehlers
//Buy on the filter crossing above its -RMS line
//Short on the filter crossing below its RMS line
//Exit long when the filter either crosses below its RMS or crosses below -RMS (which signifies a false entry signal)
//Cover short when the filter either crosses above its -RMS or crosses above RMS (which signifies a false entry signal)

study("super bandpass filter",overlay=false)
src=input(close,title="source")
bbs=input(true,"show background colors ?" )
flen=input(40)
slen=input(60)
a1= 5/flen
a2= 5/slen
PB = (a1 - a2) * close + (a2*(1 - a1) - a1 * (1 - a2))* close[1] + ((1 - a1) + (1 - a2))*nz(PB[1])- (1 - a1)* (1 - a2)*nz(PB[2])
RMSa= sum( PB*PB, 50)
RMS= sqrt(RMSa/50)
rms=-RMS
con=crossover(PB,rms) and bbs ?lime: crossunder(PB,RMS) and bbs?red:na
bgcolor(con,transp=80)
plot(PB,title="Pass Band",color=red,linewidth=2)
m=plot(RMS,title="RMS+",color=blue,linewidth=1)
s=plot(rms,title="RMS-",color=lime,linewidth=1)
fill(m,s,color=silver,transp=90)
//sbfa=nz(sbfa[1])*pow((slen-flen)+flen,2)
//sbfma=nz(sbfma[1])+sbfa*(src-nz(sbfma[1]))
//plot(sbfma,color=red,linewidth=2,title=" super bandpass filter MA")