The Lark: Directional Movement Index

study(title="TheLark: Directional Movement Index", shorttitle="DMI_LK", overlay=false)

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        //        OPEN SOURCE DMI BY THELARK           //
        //                 ~ 8-3-14 ~                 //
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        //    https://www.tradingview.com/u/TheLark    //
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// This is an open source version of the DMI or Directional Movement Index that is provided by Trading View.
// I made this mostly for other scripters to be able to modify and use, but it also helps with transparency,
// and proves that TV uses the correct Wells Wilder MA, and DMI. 

// More to come from me and modified DMI's :)

// Wells Wilders MA
wwma(l,p) =>
    wwma = (nz(wwma[1]) * (l - 1) + p) / l

// Inputs
length = input(14)

// Calc
hiDiff = high - high[1]
loDiff = low[1] - low
plusDM = (hiDiff > loDiff) and (hiDiff > 0) ? hiDiff : 0
minusDM = (loDiff > hiDiff) and (loDiff > 0) ? loDiff : 0
ATR = wwma(length, tr)
PlusDI = 100 * wwma(length,plusDM) / ATR
MinusDI = 100 * wwma(length,minusDM) / ATR
DX = (PlusDI + MinusDI > 0) ? 100 * (abs(PlusDI - MinusDI) / (PlusDI + MinusDI)) : 0

// Plots
plot(wwma(length,DX),color=#FF006E,title="DX")
plot(PlusDI, color=#0EAAEF,title="DI+")
plot(MinusDI,color=orange,title="DI-")