PositiveVolumeIndex — Positive Volume Index

A cumulative index that changes only on rising-volume bars — the crowd’s index, the mirror of NVI. Read the two together: agreement is a broad move, divergence says the crowd and the quiet money disagree.

Signature

PositiveVolumeIndex(period, on=<source>)

Argument	Type	Required	Notes
period	int Param or literal	Yes	SMA smoothing of the index. 1 returns the raw index. Bounds 1–200.
on=	symbol	No	Source symbol. Defaults to the trade symbol. Reads close and volume.

Formula

$$ \text{PVI}t = \begin{cases}\text{PVI}{t-1}\left(1 + \frac{C_t - C_{t-1}}{C_{t-1}}\right) & V_t > V_{t-1} \ \text{PVI}_{t-1} & \text{otherwise}\end{cases} $$

Warmup

Starts at 1000 and accumulates; resets per run.

Reading the value

pvi.value

Example

class CrowdFilter(Strategy):
    """Long while the crowd's index is above its own base."""
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        pvi = PositiveVolumeIndex(1, on=self.trade)
        base = EMA(255, on=pvi)
        if pvi.value > base.value and self.trade.is_flat:
            self.buy(self.trade, reason="PVI above its base")
        if pvi.value < base.value and self.trade.is_long:
            self.sell(self.trade, self.trade.position, reason="PVI below its base")

Notes

• Norman Fosback, Stock Market Logic (1976).