RSI

Summary

Wilder's Relative Strength Index, a momentum oscillator bounded 0-100 from the ratio of average gains to average losses over the period. Used to gauge overbought/oversold conditions. >70 overbought, <30 oversold.

Formula

Initial avgGain/avgLoss = simple mean of up/down moves over the period, then Wilder-smoothed each bar: \(avg = (avg_{prev}\cdot(period-1) + move)/period\). \(RSI = 100\cdot avgGain/(avgGain+avgLoss)\) (equivalent to \(100 - 100/(1+RS)\)).

Notes

In Metastock-compatibility mode an extra initial value is emitted, treating the first bar as having no gain or loss.

Inputs

inReal — Price series (typically close)

Outputs

outReal — RSI value

Parameters

optInTimePeriod — Lookback for the gain/loss averaging

Implementation

TA-Lib Definition: rsi.c · rsi.yaml

Native	File
C	`ta_RSI.c`
Rust	`rsi.rs`
Java	`Core.java`

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

Aliases

relative strength index

References

J. Welles Wilder, New Concepts in Technical Trading Systems, Trend Research (ISBN 0894590278)

RSI