Wilder Accumulative Swing Index (ASI)

Summary

Wilder's Accumulative Swing Index: the running total of the Swing Index (SI), a line meant to trace the market's real swings through the noise of the daily closes. Wilder draws trendlines and breakout points on it as on a price chart: a breakout of the ASI that the price has not confirmed yet is his signal. J. Welles Wilder Jr. introduced both in 1978. The line starts at 0 on the first bar of the requested range, so only its shape carries meaning, not its level.

Formula

$$\mathrm{ASI}_s = 0 \qquad \mathrm{ASI}_t = \mathrm{ASI}_{t-1} + \mathrm{SI}_t \quad (t > s)$$

where $s$ is the first bar of the requested range and $\mathrm{SI}_t$ is the Swing Index of bar $t$ against bar $t-1$ at the same optInLimitMove.

Notes

• Wilder accumulates Swing Index values rounded to whole numbers; the running total here is of the unrounded values.

Inputs

• inOpen — Open price of each bar
• inHigh — High price of each bar
• inLow — Low price of each bar
• inClose — Close price of each bar

Outputs

• outReal — Running total of the swing index from the first bar of the range

Parameters

Parameter	Type	Default	Accepted values	Description
optInLimitMove	real	3	≥ 0.00000001	Limit move, the largest one-bar price move the index is scaled against, in price units

Properties

Numerical Stability: Path-Dependent

☐ Overlap Input
✅ Independent Y-Axis i
☐ Candlestick
☐ Can Output NaN or ±Inf
☐ Identity at Period 1

Implementation

TA-Lib Definition: asi.c · asi.yaml

Native	File
C	ta_ASI.c
Rust	asi.rs
Java	Core_ASI.java
C#	Core_ASI.cs

TA-Lib is also available for Python, R and more using a wrapper.

Aliases

Accumulation Swing Index

See Also

SI · WAD · CUMSUM

References

• J. Welles Wilder Jr., New Concepts in Technical Trading Systems, Trend Research, 1978, section VIII "The Swing Index", pp.87-106