**petsc-3.15.0 2021-04-05**

# 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)
### Options Database Keys

### 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.

### See Also

KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPBCGSL, KSPIBCGS, KSPSetLagNorm()

### Level

beginner

### Location

src/ksp/ksp/impls/ibcgs/ibcgs.c

Index of all KSP routines

Table of Contents for all manual pages

Index of all manual pages