# Negative Volume Index (NVI)

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The theory behind the indexes is as follows: On days of increasing
volume , you can expect prices to increase, and on days of decreasing
volume , you can expect prices to decrease. This goes with the idea of
the market being in-gear and out-of-gear. Both PVI and NVI work in similar
fashions: Both are a running cumulative of values, which means you either
keep adding or subtracting price rate of change each day to the previous day`s
sum. In the case of PVI, if today`s volume is less than yesterday`s, don`t add
anything; if today`s volume is greater, then add today`s price rate of change .
For NVI , add today`s price rate of change only if today`s volume is less than
yesterday`s.
```////////////////////////////////////////////////////////////
//  Copyright by HPotter v1.0 11/06/2014
// The theory behind the indexes is as follows: On days of increasing
// volume, you can expect prices to increase, and on days of decreasing
// volume, you can expect prices to decrease. This goes with the idea of
// the market being in-gear and out-of-gear. Both PVI and NVI work in similar
// fashions: Both are a running cumulative of values, which means you either
// keep adding or subtracting price rate of change each day to the previous day`s
// sum. In the case of PVI, if today`s volume is less than yesterday`s, don`t add
// anything; if today`s volume is greater, then add today`s price rate of change.
// For NVI, add today`s price rate of change only if today`s volume is less than
// yesterday`s.
////////////////////////////////////////////////////////////
study(title="Negative Volume Index", shorttitle="Negative Volume Index")
EMA_Len = input(255, minval=1)
xROC = roc(close, 1)
nRes = iff(volume < volume[1], nz(nRes[1], 0) + xROC, nz(nRes[1], 0))
nResEMA = ema(nRes, EMA_Len)
plot(nRes, color=red, title="NVI")
plot(nResEMA, color=blue, title="EMA")
```

## Bình luận

very good , Thanks !
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yanyancha
@yanyancha, You are welcome.
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HPotter
@HPotter, so this acts like net volume index just one for long and one for short so to speak
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