From afcd7e88b6610bcd8dd504f43ce6fe545048242d Mon Sep 17 00:00:00 2001 From: Martin Kroeker Date: Mon, 21 Nov 2022 21:18:39 +0100 Subject: [PATCH] Improve convergence of DLAED4/SLAED4 (Reference-LAPACK PR655) --- lapack-netlib/SRC/dlaed4.f | 7 +++++-- lapack-netlib/SRC/slaed4.f | 7 +++++-- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/lapack-netlib/SRC/dlaed4.f b/lapack-netlib/SRC/dlaed4.f index 3ee3ef920..b51e23d85 100644 --- a/lapack-netlib/SRC/dlaed4.f +++ b/lapack-netlib/SRC/dlaed4.f @@ -328,9 +328,12 @@ IF( C.LT.ZERO ) $ C = ABS( C ) IF( C.EQ.ZERO ) THEN -* ETA = B/A +* ETA = B/A * ETA = RHO - TAU - ETA = DLTUB - TAU +* ETA = DLTUB - TAU +* +* Update proposed by Li, Ren-Cang: + ETA = -W / ( DPSI+DPHI ) ELSE IF( A.GE.ZERO ) THEN ETA = ( A+SQRT( ABS( A*A-FOUR*B*C ) ) ) / ( TWO*C ) ELSE diff --git a/lapack-netlib/SRC/slaed4.f b/lapack-netlib/SRC/slaed4.f index f056746d8..339c5029c 100644 --- a/lapack-netlib/SRC/slaed4.f +++ b/lapack-netlib/SRC/slaed4.f @@ -328,9 +328,12 @@ IF( C.LT.ZERO ) $ C = ABS( C ) IF( C.EQ.ZERO ) THEN -* ETA = B/A +* ETA = B/A * ETA = RHO - TAU - ETA = DLTUB - TAU +* ETA = DLTUB - TAU +* +* Update proposed by Li, Ren-Cang: + ETA = -W / ( DPSI+DPHI ) ELSE IF( A.GE.ZERO ) THEN ETA = ( A+SQRT( ABS( A*A-FOUR*B*C ) ) ) / ( TWO*C ) ELSE