Downside upside volatility

// This source code is subject to the terms of the Mozilla Public License 2.0 at https://mozilla.org/MPL/2.0/
// © Motgench

//@version=4
study("Pig Downside Upside Volatility",precision=2)

sd(src, length) =>
    deviation = src - sma(src, length)
    variance = sum(pow(deviation, 2), length) / (length)
    sd=sqrt(variance)

Annual = input(365, "Annual")
n = input(30, "Length")
xPrice = log(close/nz(close[1]))
d = 0.0

if xPrice < 0
    d := log(close/nz(close[1]))


dhv = sd(d,n)* sqrt(Annual) * 100

u = 0.0
if xPrice > 0
    u := log(close/nz(close[1]))

uhv = sd(u,n)*sqrt(Annual)*100

nethv = uhv - dhv
len = input(30,title="band length")
sdnet = sd(nethv,len)
sma = sma(nethv,len)
upsd = sma + 1.96*sdnet
downsd = sma - 1.96*sdnet
Color = nethv > 0 ? color.green : color.red
sn = input(false,"Show net volatility")
sb = input(false,"Show band")
plot(sn? na : dhv,color= color.red,title="downside volatility")
plot(sn?na:uhv,color=color.green,title = "upside volatility")
plot(sn?nethv:na,color=Color,title = "net volatility",style=plot.style_columns)
hline(0)
plot(sb and sn?upsd:na,color=color.aqua,title="upband")
plot(sb and sn?downsd:na,color=color.aqua,title="downband")
plot(sn?sma:na,color=color.white,title="mean")