# KSPIBCGS#

Implements the IBiCGStab (Improved Stabilized version of BiConjugate Gradient) method in an alternative form to have only a single global reduction operation instead of the usual 3 (or 4)

## Notes#

Supports left and right preconditioning

See KSPBCGSL for additional stabilization

Unlike the Bi-CG-stab algorithm, this requires one multiplication be the transpose of the operator before the iteration starts.

The paper has two errors in the algorithm presented, they are fixed in the code in KSPSolve_IBCGS()

For maximum reduction in the number of global reduction operations, this solver should be used with KSPSetLagNorm().

This is not supported for complex numbers.

## Reference#

The Improved BiCGStab Method for Large and Sparse Unsymmetric Linear Systems on Parallel Distributed Memory Architectures. L. T. Yang and R. Brent, Proceedings of the Fifth International Conference on Algorithms and Architectures for Parallel Processing, 2002, IEEE.

KSP: Linear System Solvers, KSPCreate(), KSPSetType(), KSPType, KSP, KSPBICG, KSPBCGSL, KSPIBCGS, KSPSetLagNorm()