mql5/Indicators/MyIndicators/TSI_Pro.md

True Strength Index (TSI) Professional

1. Summary (Introduction)

The True Strength Index (TSI), developed by William Blau, is a momentum oscillator designed to provide a smoother and more reliable measure of market momentum by using a double-smoothing mechanism with Exponential Moving Averages (EMAs). It fluctuates around a zero line, providing clear signals for trend direction, momentum, and overbought/oversold conditions.

Our TSI_Pro implementation is a unified, professional version that allows the calculation to be based on either standard or Heikin Ashi price data, selectable from a single input parameter.

2. Mathematical Foundations and Calculation Logic

The TSI is calculated by double-smoothing both the price momentum and the absolute price momentum, and then computing their ratio.

Required Components

• Slow Period (N_slow): The period for the first, longer-term EMA smoothing (standard is 25).
• Fast Period (N_fast): The period for the second, shorter-term EMA smoothing (standard is 13).
• Signal Period: The period for the moving average signal line.
• Source Price (P): The price series used for the calculation.

Calculation Steps (Algorithm)

1. Calculate Price Momentum: For each bar, calculate the change in price from the previous bar. \text{Momentum}_i = P_i - P_{i-1}
2. First EMA Smoothing (Slow Period): Apply an N_slow-period EMA to both the Momentum and its absolute value.
3. Second EMA Smoothing (Fast Period): Apply an N_fast-period EMA to the results of the first smoothing step.
4. Calculate the TSI Value: Divide the double-smoothed momentum by the double-smoothed absolute momentum and scale the result to 100. \text{TSI}_i = 100 \times \frac{\text{EMA}_{\text{fast}}(\text{EMA}_{\text{slow}}(\text{Momentum}))_i}{\text{EMA}_{\text{fast}}(\text{EMA}_{\text{slow}}(\text{AbsMomentum}))_i}
5. Calculate the Signal Line: The signal line is a moving average of the TSI line itself.

3. MQL5 Implementation Details

Our MQL5 implementation follows a modern, object-oriented design to ensure stability, reusability, and maintainability.

• Modular Calculation Engine (TSI_Calculator.mqh): The entire calculation logic is encapsulated within a reusable include file.

  • CTSICalculator: The base class that performs the full, multi-stage TSI calculation on a given source price.
  • CTSICalculator_HA: A child class that inherits all the complex logic and only overrides the initial data preparation step to use smoothed Heikin Ashi prices as its input. This object-oriented approach eliminates code duplication.

• Stability via Full Recalculation: We employ a "brute-force" full recalculation within OnCalculate. For a complex, multi-stage indicator like the TSI, this is the most reliable method to prevent calculation errors.

• Fully Manual EMA Calculations: All EMA calculations are performed manually, with robust initialization to provide a stable starting point for the calculation chain.

• Flexible Signal Line: The indicator includes a user-configurable moving average signal line, with a robust switch block that correctly handles all MA types (SMA, EMA, SMMA, LWMA).

4. Parameters

• Slow Period (InpSlowPeriod): The period for the first, longer-term EMA smoothing. Default is 25.
• Fast Period (InpFastPeriod): The period for the second, shorter-term EMA smoothing. Default is 13.
• Applied Price (InpSourcePrice): The source price for the calculation. This unified dropdown menu allows you to select from all standard and Heikin Ashi price types.
• Signal Line Settings:
  • InpSignalPeriod: The lookback period for the signal line. Default is 13.
  • InpSignalMAType: The type of moving average for the signal line. Default is MODE_EMA.

5. Usage and Interpretation

• Zero Line Crossovers: A crossover of the TSI line above the zero line indicates that long-term momentum has turned positive. A crossover below indicates negative momentum.
• Signal Line Crossovers: These provide earlier, shorter-term momentum signals. A bullish crossover is when the TSI line crosses above its signal line; a bearish crossover is the opposite.
• Overbought/Oversold Levels: The +25 and -25 levels are often used to identify extreme momentum.
• Divergence: Due to its smoothness, the TSI is excellent for spotting divergences between price and momentum, which can foreshadow reversals.