TD Lines (TDST)

TD Setup Trend support / resistance levels. Once a TD Setup completes in either direction, DeMark defines two horizontal trend levels derived from the nine bars of that setup: TDST resistance = the highest high of a completed buy setup; TDST support = the lowest low of a completed sell setup. A break of these levels invalidates the corresponding setup's reversal thesis.

Quick reference

Item	Value
Family	DeMark
Input type	Candle
Output type	TdLinesOutput { resistance, support } (both f64, NaN initially)
Output range	unbounded (price-units), or NaN
Default parameters	lookback = 4, target = 9 (same as TdSetup)
Warmup period	lookback + 1
Interpretation	Break invalidates the corresponding setup's reversal thesis

Formula

TDST_resistance = max(high) over the 9 bars of the most recently
                  completed buy setup

TDST_support    = min(low) over the 9 bars of the most recently
                  completed sell setup

Until a setup completes in a given direction, the corresponding level is f64::NAN (no level defined). Once a level is set it stays at its value until the next completed setup in that direction updates it. See crates/wickra-core/src/indicators/td_lines.rs.

Parameters

Name	Type	Default	Constraint	Description
lookback	usize	4	> 0	Setup-phase close-vs-close lookback.
target	usize	9	> 0	Setup completion target.

TdLines::new returns Error::PeriodZero for zero arguments.

Inputs / Outputs

Indicator<Input = Candle, Output = TdLinesOutput> with fields:

Field	Description
resistance	TDST resistance from the most recent completed buy setup. NaN if none yet.
support	TDST support from the most recent completed sell setup. NaN if none yet.

Python: (n, 2) array, columns [resistance, support] with NaN-filled warmup. Node: flat number[] interleaved.

Warmup

warmup_period() == lookback + 1. The setup runs from bar lookback + 1; TDST emits only on bars where at least one setup has completed — initial output is (NaN, NaN).

Edge cases

• No setup completed yet. Both fields are NaN.
• Both setups completed. Both fields hold the most recent level for their direction.
• NaN comparison. Downstream code must explicitly check is_nan() before comparing — x > NaN is always false in IEEE 754.
• Setup running stats. The implementation tracks the running max-high (for buy setup) and min-low (for sell setup) during the active streak so the level can be emitted immediately on setup completion.
• Reset. Clears all internal state.

Examples

Rust

use wickra::{BatchExt, Candle, Indicator, TdLines};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let prices: Vec<f64> = (0..30).map(|i| 100.0 - f64::from(i) * 0.5).collect();
    let candles: Vec<Candle> = prices.iter().enumerate()
        .map(|(i, &c)| Candle::new(c, c + 0.5, c - 0.5, c, 1.0, i as i64).unwrap())
        .collect();
    let mut tl = TdLines::new(4, 9)?;
    if let Some(o) = tl.batch(&candles)[25] {
        println!("resistance = {} (NaN if no buy setup yet)", o.resistance);
        println!("support    = {}", o.support);
    }
    Ok(())
}

Python

import numpy as np
import wickra as ta

close = 100 - np.arange(30, dtype=float) * 0.5
tl = ta.TdLines(4, 9)
out = tl.batch(close + 0.5, close - 0.5, close)
print('row 25:', out[25])  # [resistance, support]

Node

const wickra = require('wickra');
const tl = new wickra.TdLines(4, 9);
const close = Array.from({ length: 30 }, (_, i) => 100 - i * 0.5);
const flat = tl.batch(close.map(c => c + 0.5), close.map(c => c - 0.5), close);
console.log('row 25 resistance:', flat[25 * 2]);
console.log('row 25 support   :', flat[25 * 2 + 1]);

Streaming

use wickra::{Candle, Indicator, TdLines};

let mut tl = TdLines::classic();
let candle_stream: Vec<Candle> = Vec::new(); // your live OHLCV feed
for bar in candle_stream {
    if let Some(o) = tl.update(bar) {
        if !o.resistance.is_nan() && bar.close > o.resistance {
            // Buy setup invalidated — bullish breakout above TDST
        }
        if !o.support.is_nan() && bar.close < o.support {
            // Sell setup invalidated — bearish breakdown below TDST
        }
    }
}

Interpretation

• Setup invalidation levels. TDST resistance is where a completed buy setup's reversal thesis fails — a break above signals the bears have lost. TDST support is the mirror for sell setups.
• Pairs with Sequential / Combo. A buy Countdown 13 or Combo 13 should be invalidated if price subsequently closes above TDST resistance — that's how DeMark traders handle stops.
• Trend confirmation. Persistent moves through TDST (not retesting it) suggest the setup's exhaustion thesis was wrong and the original trend was stronger than detected.

Common pitfalls

• Forgetting NaN. Output fields are NaN until the first setup in that direction completes. Comparisons silently fail in most languages — gate explicitly.
• Wrong direction usage. resistance comes from buy setups (the highest high during the buy streak); support from sell setups. Don't swap.
• Using TDST as primary entry signal. It's an invalidation level, not a setup. Generate entries from Setup/Countdown; use TDST for stop / target placement.

References

• Tom DeMark, DeMark Indicators (with Jason Perl, 2008) — formal TDST treatment.

See also

• TdSetup — the setup phase TDST is derived from.
• TdSequential — TDST is used as invalidation for completed Sequentials.
• TdRiskLevel — alternative stop formulation.
• Indicators-Overview — full taxonomy.