DEnvelope Bandwidth [TradingView Custom Indicator]

//
// @author LazyBear
// List of all my indicators: https://www.tradingview.com/v/4IneGo8h/
//
study("DEnvelope Bandwidth [LazyBear]", shorttitle="DENVBW_LB")
lb=input(20, title="DEnvelope lookback length")
de=input(2, title="DEnvelope band deviation")
alp=2/(lb+1)
src=hlc3
mt=alp*src+(1-alp)*nz(mt[1])
ut=alp*mt+(1-alp)*nz(ut[1])
dt=((2-alp)*mt-ut)/(1-alp)
mt2=alp*abs(src-dt)+(1-alp)*nz(mt2[1])
ut2=alp*mt2+(1-alp)*nz(ut2[1])
dt2=((2-alp)*mt2-ut2)/(1-alp)
but=dt+de*dt2
blt=dt-de*dt2
bbw = (but-blt)/dt
plot(bbw, color=blue, linewidth=2)