Add iterative solver options (BiCGSTAB, GMRES, IDR(s)) to ripple solver

[krystophny]

Summary

Add iterative solver options to the ripple solver by leveraging the generic sparse iterative solvers.

Background

Once we have generic sparse iterative solvers (#48), we can use them in the ripple solver as alternatives to the current Arnoldi-Richardson method.

Dependencies

• Depends on Add iterative solver methods to sparse solver module #48 (sparse iterative solvers) for the solver implementations
• Depends on Refactor ripple solver for testability and modularity #45 (ripple solver refactoring) for clean interfaces
• Depends on Add testing and code coverage infrastructure #50 (testing infrastructure)

Tasks

• Add solver selection interface (isw_ripple_solver parameter)
• Integrate BiCGSTAB from sparse solver module
• Integrate GMRES from sparse solver module
• Integrate IDR(s) from sparse solver module
• Adapt preconditioning for ripple-specific matrices
• Add convergence monitoring specific to ripple problem
• Comprehensive testing and validation
• Performance comparison with Arnoldi method

Implementation Strategy

1. Build on Refactor ripple solver for testability and modularity #45 and Add iterative solver methods to sparse solver module #48
2. Use the generic sparse iterative solvers within Arnoldi iteration
3. Each Arnoldi step calls the selected iterative solver
4. Maintain backward compatibility (Arnoldi remains default)

Solver Options

• isw_ripple_solver=1: Original Arnoldi-Richardson (default)
• isw_ripple_solver=2: Arnoldi with BiCGSTAB for inner solve
• isw_ripple_solver=3: Arnoldi with GMRES for inner solve
• isw_ripple_solver=4: Arnoldi with IDR(s) for inner solve

Testing Requirements

• Unit tests for each solver option
• Convergence tests with different problem types
• Performance comparisons
• Golden record validation with each solver
• Physics results must be identical

Related Work

• Uses iterative solvers from Add iterative solver methods to sparse solver module #48
• Different approach than Replace nested sparse solver calls in ripple solver with direct iterative methods #49 (keeps Arnoldi structure)