From 27bef224d9e4e8fdadc0e33d70c98d9a10a0d149 Mon Sep 17 00:00:00 2001
From: james <james@8a072113-8704-0410-8d35-dd094bca7971>
Date: Thu, 24 Feb 2011 21:12:23 +0000
Subject: [PATCH] changed matrix norm to 'M' (max) from 'I' (inf) for scaling
 of input matrix and added check for zero norm in xSTERF (the xSTEQR already
 had this check) this fixes the issue reported in bug0036

---
 SRC/dsteqr.f | 2 +-
 SRC/dsterf.f | 9 ++++++---
 SRC/ssteqr.f | 2 +-
 SRC/ssterf.f | 4 +++-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/SRC/dsteqr.f b/SRC/dsteqr.f
index a0ec5cdb..17a17468 100644
--- a/SRC/dsteqr.f
+++ b/SRC/dsteqr.f
@@ -195,7 +195,7 @@
 *
 *     Scale submatrix in rows and columns L to LEND
 *
-      ANORM = DLANST( 'I', LEND-L+1, D( L ), E( L ) )
+      ANORM = DLANST( 'M', LEND-L+1, D( L ), E( L ) )
       ISCALE = 0
       IF( ANORM.EQ.ZERO )
      $   GO TO 10
diff --git a/SRC/dsterf.f b/SRC/dsterf.f
index 4f2a9bcf..74f289b6 100644
--- a/SRC/dsterf.f
+++ b/SRC/dsterf.f
@@ -54,7 +54,7 @@
      $                   NMAXIT
       DOUBLE PRECISION   ALPHA, ANORM, BB, C, EPS, EPS2, GAMMA, OLDC,
      $                   OLDGAM, P, R, RT1, RT2, RTE, S, SAFMAX, SAFMIN,
-     $                   SIGMA, SSFMAX, SSFMIN
+     $                   SIGMA, SSFMAX, SSFMIN, RMAX
 *     ..
 *     .. External Functions ..
       DOUBLE PRECISION   DLAMCH, DLANST, DLAPY2
@@ -90,6 +90,7 @@
       SAFMAX = ONE / SAFMIN
       SSFMAX = SQRT( SAFMAX ) / THREE
       SSFMIN = SQRT( SAFMIN ) / EPS2
+      RMAX = DLAMCH( 'O' )
 *
 *     Compute the eigenvalues of the tridiagonal matrix.
 *
@@ -128,9 +129,11 @@
 *
 *     Scale submatrix in rows and columns L to LEND
 *
-      ANORM = DLANST( 'I', LEND-L+1, D( L ), E( L ) )
+      ANORM = DLANST( 'M', LEND-L+1, D( L ), E( L ) )
       ISCALE = 0
-      IF( ANORM.GT.SSFMAX ) THEN
+      IF( ANORM.EQ.ZERO )
+     $   GO TO 10      
+      IF( (ANORM.GT.SSFMAX) ) THEN
          ISCALE = 1
          CALL DLASCL( 'G', 0, 0, ANORM, SSFMAX, LEND-L+1, 1, D( L ), N,
      $                INFO )
diff --git a/SRC/ssteqr.f b/SRC/ssteqr.f
index 952fb502..835c82fc 100644
--- a/SRC/ssteqr.f
+++ b/SRC/ssteqr.f
@@ -195,7 +195,7 @@
 *
 *     Scale submatrix in rows and columns L to LEND
 *
-      ANORM = SLANST( 'I', LEND-L+1, D( L ), E( L ) )
+      ANORM = SLANST( 'M', LEND-L+1, D( L ), E( L ) )
       ISCALE = 0
       IF( ANORM.EQ.ZERO )
      $   GO TO 10
diff --git a/SRC/ssterf.f b/SRC/ssterf.f
index a51c379d..b9110dd6 100644
--- a/SRC/ssterf.f
+++ b/SRC/ssterf.f
@@ -128,8 +128,10 @@
 *
 *     Scale submatrix in rows and columns L to LEND
 *
-      ANORM = SLANST( 'I', LEND-L+1, D( L ), E( L ) )
+      ANORM = SLANST( 'M', LEND-L+1, D( L ), E( L ) )
       ISCALE = 0
+      IF( ANORM.EQ.ZERO )
+     $   GO TO 10      
       IF( ANORM.GT.SSFMAX ) THEN
          ISCALE = 1
          CALL SLASCL( 'G', 0, 0, ANORM, SSFMAX, LEND-L+1, 1, D( L ), N,
-- 
2.34.1