TradingView Indicator: Choppiness Index

study("TheLark: Choppiness Index", overlay=false)

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//        CHOPPINESS INDEX BY THELARK          //
//                 ~ 4-23-14 ~                 //
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//                     •/•                     //
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//    https://www.tradingview.com/u/TheLark    //
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//•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•/•//

length = input(14, title="Length")
doavg = input(true,title="Do Average?")
avg = input(4, title="Average Length")
l1 = input(61.8, title="Extreme Chop")
l2 = input(50.0, title="Midline")
l3 = input(38.2, title="Trending")

str = sum(tr,length)
ltl = lowest(low <= close[1] ? low : close[1],length)
hth = highest(high >= close[1] ? high : close[1],length)
height = hth - ltl
chop = 100 * (log10(str / height) / log10(length))

plot(chop, color=#42B0FF, linewidth=2)
plot(doavg ? sma(chop,avg) : na, color=white)
hli1 = plot(l1, color=gray)
hli2 = plot(l2, color=gray)
hli3 = plot(l3, color=gray)

fill(hli1,hli2,black,80)
fill(hli2,hli3,#C8D974,80)