Vortex Indicator (VI) - Built-in Indicator Guide

Computes two lines (VI+ and VI-) measuring positive and negative trend movements.

Overview

The Vortex Indicator assesses trend strength and direction by comparing the range of price movement over a defined period. It produces two oscillating lines: VI+ (blue) that captures upward trend momentum and VI- (red) that captures downward trend momentum. When VI+ crosses above VI-, an uptrend is indicated; the reverse signals a downtrend. Values near 1 denote a strong trend in the respective direction.

The indicator is typically used to identify trend reversals and confirm price action. It works best in trending markets and can generate false signals in choppy, range-bound conditions.

How it works

1. Compute VM- as the sum of the absolute difference between the current low and the previous high over length bars.
2. Compute VM+ as the sum of the absolute difference between the current high and the previous low over length bars.
3. Compute the sum of the True Range (ATR with period 1) over the same length bars.
4. Divide VM- by the ATR sum to obtain VI- (negative direction indicator).
5. Divide VM+ by the ATR sum to obtain VI+ (positive direction indicator).
6. Return the two values as separate series, drawn as red and blue lines respectively.

Mathematical model

Parameters

Code walkthrough

Indicator Decorators and Parameters

Lines 7-11 of Vortex Indicator.indie5:

@indicator('VI', format=format.PRICE, precision=4)  # Vortex Indicator
@param.int('length', default=14, min=2)
@plot.line(color=color.RED, title='VI -')
@plot.line(color=color.BLUE, title='VI +')
def Main(self, length):

The @indicator decorator names the script ‘VI’ and sets display precision to 4 decimal places. The @param.int defines a user‑adjustable length (default 14, minimum 2). Two @plot.line decorators assign colors (red for VI–, blue for VI+) and titles for the chart legend.

Computing VM+ and VM− Using Rolling Sums

Lines 12-13 of Vortex Indicator.indie5:

    vmm = Sum.new(MutSeriesF.new(abs(self.low[0] - self.high[1])), length)[0]
    vmp = Sum.new(MutSeriesF.new(abs(self.high[0] - self.low[1])), length)[0]

Each line creates a MutSeriesF to hold the per‑bar absolute difference (abs(self.low[0] - self.high[1]) for VM−, abs(self.high[0] - self.low[1]) for VM+). This series is fed into Sum.new(…, length)[0], which returns a trailing sum over the last length bars. The [0] index fetches the current bar’s sum value.

Normalizing with ATR

Lines 14-17 of Vortex Indicator.indie5:

    satr = Sum.new(Atr.new(1), length)[0]
    vim = divide(vmm, satr)
    vip = divide(vmp, satr)
    return vim, vip

A separate sum of the True Range (Atr.new(1)) over the same window provides the denominator. The divide function safely calculates VI− = VM− / ATR and VI+ = VM+ / ATR, handling division‑by‑zero. The return statement packs both values into a tuple as required by the @plot.line decorators.

Reading the chart

• Red line (VI−): measures downward trend strength. Values above the blue line suggest a bearish trend.
• Blue line (VI+): measures upward trend strength. Values above the red line suggest a bullish trend.
• Crossovers: when VI+ crosses above VI− it may signal the start of an uptrend; when VI− crosses above VI+ it may signal a downtrend.
• Magnitude: values near 1.0 indicate a strong trend in the corresponding direction; values near 0.3–0.5 suggest weak or absent trend.

Implementation notes

• The indicator uses one bar of look‑back for the high/low differences because it references high[1] and low[1] (previous bar), so the first bar of data will produce NaN.
• Sum.new implements a rolling sum (not an exponential average), matching the classic Vortex definition.
• The divide function returns math.nan when the denominator is zero, preventing division‑by‑zero errors.
• Atr.new(1) computes the True Range (TR) without the usual Wilder smoothing—smoothing is achieved by the subsequent sum over length bars.

FAQ

What is the recommended length for daily charts?

The default of 14 is widely used and matches the original Vortex publication. Shorter lengths (e.g., 7) make the indicator more sensitive to price movements, while longer lengths (e.g., 21) smooth out noise.

Can I change the colors of the VI lines?

Yes. Modify the color parameters in the @plot.line decorators (lines 9 and 10). Replace color.RED or color.BLUE with any available color constant or hex string.

Why does the indicator show NaN on the first few bars?

The rolling sum requires length values before it can produce a valid result. Additionally, the indicator references the previous bar’s high/low, so the very first bar cannot compute a difference. Both factors lead to initial NaN values.

Full source code

Indie Script v5, the built-in indicator as shipped with TakeProfit. Add it from the indicators menu or copy the code into the platform’s script editor.

# indie:lang_version = 5
from indie import indicator, format, param, plot, color, MutSeriesF
from indie.algorithms import Sum, Atr
from indie.math import divide


@indicator('VI', format=format.PRICE, precision=4)  # Vortex Indicator
@param.int('length', default=14, min=2)
@plot.line(color=color.RED, title='VI -')
@plot.line(color=color.BLUE, title='VI +')
def Main(self, length):
    vmm = Sum.new(MutSeriesF.new(abs(self.low[0] - self.high[1])), length)[0]
    vmp = Sum.new(MutSeriesF.new(abs(self.high[0] - self.low[1])), length)[0]
    satr = Sum.new(Atr.new(1), length)[0]
    vim = divide(vmm, satr)
    vip = divide(vmp, satr)
    return vim, vip