zeonta.pvi() — Cumulative index that only moves on a bar where volume rose versus the prior bar.
What it measures
The mirror-image complement of nvi: only updates on a bar where volume rose versus the bar before it, holding flat through every quiet-volume bar. Built on the same Dysart/Fosback idea, from the opposite side — heavy volume days reflect crowd-driven activity rather than informed money.
Formula
Starts at 1000. When Volume[i] > Volume[i-1]: PVI[i] = PVI[i-1] * (1 + (Close[i]-Close[i-1])/Close[i-1]); otherwise unchanged
Parameters
Required inputs: close, volume
None.
Returns
| Column |
|---|
PVI |
Usage
Examples run against the 300-bar OHLCV fixture in tests/data/ohlcv.csv, loaded as df. The output shown is the real output.
import pandas as pd
import zeonta
df = pd.read_csv('tests/data/ohlcv.csv', parse_dates=['date']).set_index('date')
zeonta.pvi(df['close'], df['volume']).tail(3)
date
2024-10-25 830.069322
2024-10-26 830.069322
2024-10-27 830.069322
Name: PVI, dtype: float64
Accessor form: df.zta.pvi(...)
How to read it
Read the opposite way from NVI in the classic Fosback framework: PVI is treated as the noisier, crowd-driven half of the pair, so less weight is typically put on it alone than on NVI’s own long-run signal.
Pitfalls
Same starting-value caveat as nvi: 1000 is StockCharts’/Fidelity’s convention, not a universal constant — compare a PVI series only against itself.
Reference
Formula source: https://www.fidelity.com/learning-center/trading-investing/technical-analysis/technical-indicator-guide/positive-volume-index