From 93ff388841b11694bc16dfbd79bcf6136383a376 Mon Sep 17 00:00:00 2001
From: mehmet alper kuyumcu <m.alperkuyumcu@gmail.com>
Date: Thu, 29 Jan 2026 16:59:38 +0000
Subject: [PATCH] Fix relative tolerance scaling by multiplying with RHS norm
 in BiCGSTAB

libeigen/eigen!2118
---
 Eigen/src/IterativeLinearSolvers/BiCGSTAB.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h b/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h
index 8fdeb849b..2d461fe07 100644
--- a/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h
+++ b/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h
@@ -34,7 +34,6 @@ bool bicgstab(const MatrixType& mat, const Rhs& rhs, Dest& x, const Precondition
   typedef typename Dest::RealScalar RealScalar;
   typedef typename Dest::Scalar Scalar;
   typedef Matrix<Scalar, Dynamic, 1> VectorType;
-  RealScalar tol = tol_error;
   Index maxIters = iters;
 
   Index n = mat.cols();
@@ -48,6 +47,9 @@ bool bicgstab(const MatrixType& mat, const Rhs& rhs, Dest& x, const Precondition
     x.setZero();
     return true;
   }
+
+  RealScalar tol = tol_error * rhs_norm;
+
   Scalar rho(1);
   Scalar alpha(0);
   Scalar w(1);