Context

Implements iterative calculation for circular references, similar to Microsoft Excel and Google Sheets.

When iterativeCalculationEnable is set to true, circular references are resolved using Gauss-Seidel iteration instead of returning #CYCLE! errors. The algorithm:

1. Initializes all cycle cells to iterativeCalculationInitialValue
2. Repeatedly evaluates cycle cells in address order until convergence or max iterations
3. Convergence: all cell changes are < iterativeCalculationConvergenceThreshold
4. Updates dependents of cycle cells after stabilization

New configuration options:

• iterativeCalculationEnable (boolean, default: false) - Enable iterative calculation
• iterativeCalculationMaxIterations (number, default: 100) - Maximum iterations before stopping
• iterativeCalculationConvergenceThreshold (number, default: 0.001) - Convergence threshold
• iterativeCalculationInitialValue (RawCellContent, default: 0) - Starting value for cycle cells

How did you test your changes?

• 54 unit tests covering:
  • Simple self-references (A1=A1+1)
  • Multi-cell cycles (A1→B1→A1)
  • Convergence scenarios (A1=B1/2, B1=A1/2)
  • Non-convergent/oscillating formulas
  • Error propagation in cycles
  • Config validation (invalid types, out-of-range values)
  • Partial recalculation with cycles
  • Mixed cycles with ranges and SUM functions
  • Different initial values (0, strings, booleans)

Types of changes

• New feature or improvement (a non-breaking change that adds functionality)

Related issues:

1. Fixes Feature: Iterative Calculation #1545

Checklist:

• I have reviewed the guidelines about Contributing to HyperFormula and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement.
• My change is compliant with the OpenDocument standard.
• My change is compatible with Microsoft Excel.
• My change is compatible with Google Sheets.
• I described my changes in the CHANGELOG.md file.
• My changes require a documentation update.
• My changes require a migration guide.