{D,Z}BBCSD: stricter zero criterion

The tolerance below which matrix entries are considered zero is tightened to avoid insufficiently accurate singular vectors. fixes Reference-LAPACK#965
christoph-conrads · Dec 29, 2023 · 1d6b882 · 1d6b882
1 parent db501d9
commit 1d6b882
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Showing 2 changed files with 4 additions and 4 deletions.
diff --git a/SRC/dbbcsd.f b/SRC/dbbcsd.f
@@ -302,7 +302,7 @@
 *  =========================
 *>
 *> \verbatim
-*>  TOLMUL  DOUBLE PRECISION, default = MAX(10,MIN(100,EPS**(-1/8)))
+*>  TOLMUL  DOUBLE PRECISION, default = 10
 *>          TOLMUL controls the convergence criterion of the QR loop.
 *>          Angles THETA(i), PHI(i) are rounded to 0 or PI/2 when they
 *>          are within TOLMUL*EPS of either bound.
@@ -451,7 +451,7 @@ SUBROUTINE DBBCSD( JOBU1, JOBU2, JOBV1T, JOBV2T, TRANS, M, P, Q,
 *
       EPS = DLAMCH( 'Epsilon' )
       UNFL = DLAMCH( 'Safe minimum' )
-      TOLMUL = MAX( TEN, MIN( HUNDRED, EPS**MEIGHTH ) )
+      TOLMUL = TEN
       TOL = TOLMUL*EPS
       THRESH = MAX( TOL, MAXITR*Q*Q*UNFL )
 *

diff --git a/SRC/zbbcsd.f b/SRC/zbbcsd.f
@@ -302,7 +302,7 @@
 *  =========================
 *>
 *> \verbatim
-*>  TOLMUL  DOUBLE PRECISION, default = MAX(10,MIN(100,EPS**(-1/8)))
+*>  TOLMUL  DOUBLE PRECISION, default = 10
 *>          TOLMUL controls the convergence criterion of the QR loop.
 *>          Angles THETA(i), PHI(i) are rounded to 0 or PI/2 when they
 *>          are within TOLMUL*EPS of either bound.
@@ -450,7 +450,7 @@ SUBROUTINE ZBBCSD( JOBU1, JOBU2, JOBV1T, JOBV2T, TRANS, M, P, Q,
 *
       EPS = DLAMCH( 'Epsilon' )
       UNFL = DLAMCH( 'Safe minimum' )
-      TOLMUL = MAX( TEN, MIN( HUNDRED, EPS**MEIGHTH ) )
+      TOLMUL = TEN
       TOL = TOLMUL*EPS
       THRESH = MAX( TOL, MAXITR*Q*Q*UNFL )
 *