Fix bug 139 submitted by Christoph Conrads on Oct 6th 2015

"according to the LAPACK documentation, xSTEDC guarantees to
return the eigenvalues in ascending order (parameter D on exit). To
this end, it sorts the eigenvalues if necessary.

If there is only a single subproblem of size n, no sorting algorithm is
called (cf. {s,d}tedc.f, line 450). Furthermore, xLAED0
({s,d}tedc.f:400) does not guarantee to return eigenvalues in ascending
order. Thus, xSTEDC may return eigenvalues that are not in ascending
order."

Applied patch provided by Christoph Conrads: "always sorting the eigenvalues"

diff --git a/SRC/cstedc.f b/SRC/cstedc.f
index 5bf442f..acaae58 100644 (file)
--- a/SRC/cstedc.f
+++ b/SRC/cstedc.f
@@ -453,31 +453,25 @@
 *
 *        endwhile
 *
-*        If the problem split any number of times, then the eigenvalues
-*        will not be properly ordered.  Here we permute the eigenvalues
-*        (and the associated eigenvectors) into ascending order.
-*
-         IF( M.NE.N ) THEN
-*
-*           Use Selection Sort to minimize swaps of eigenvectors
-*
-            DO 60 II = 2, N
-               I = II - 1
-               K = I
-               P = D( I )
-               DO 50 J = II, N
-                  IF( D( J ).LT.P ) THEN
-                     K = J
-                     P = D( J )
-                  END IF
-   50          CONTINUE
-               IF( K.NE.I ) THEN
-                  D( K ) = D( I )
-                  D( I ) = P
-                  CALL CSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
-               END IF
-   60       CONTINUE
-         END IF
+*
+*        Use Selection Sort to minimize swaps of eigenvectors
+*
+         DO 60 II = 2, N
+           I = II - 1
+           K = I
+           P = D( I )
+           DO 50 J = II, N
+              IF( D( J ).LT.P ) THEN
+                 K = J
+                 P = D( J )
+              END IF
+   50      CONTINUE
+           IF( K.NE.I ) THEN
+              D( K ) = D( I )
+              D( I ) = P
+              CALL CSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
+           END IF
+   60    CONTINUE
       END IF
 *
    70 CONTINUE

diff --git a/SRC/dstedc.f b/SRC/dstedc.f
index ddfe13e..b97e16b 100644 (file)
--- a/SRC/dstedc.f
+++ b/SRC/dstedc.f
@@ -443,38 +443,32 @@
 *
 *        endwhile
 *
-*        If the problem split any number of times, then the eigenvalues
-*        will not be properly ordered.  Here we permute the eigenvalues
-*        (and the associated eigenvectors) into ascending order.
+         IF( ICOMPZ.EQ.0 ) THEN
 *
-         IF( M.NE.N ) THEN
-            IF( ICOMPZ.EQ.0 ) THEN
+*          Use Quick Sort
 *
-*              Use Quick Sort
+           CALL DLASRT( 'I', N, D, INFO )
 *
-               CALL DLASRT( 'I', N, D, INFO )
-*
-            ELSE
+         ELSE
 *
-*              Use Selection Sort to minimize swaps of eigenvectors
-*
-               DO 40 II = 2, N
-                  I = II - 1
-                  K = I
-                  P = D( I )
-                  DO 30 J = II, N
-                     IF( D( J ).LT.P ) THEN
-                        K = J
-                        P = D( J )
-                     END IF
-   30             CONTINUE
-                  IF( K.NE.I ) THEN
-                     D( K ) = D( I )
-                     D( I ) = P
-                     CALL DSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
-                  END IF
-   40          CONTINUE
-            END IF
+*          Use Selection Sort to minimize swaps of eigenvectors
+*
+           DO 40 II = 2, N
+              I = II - 1
+              K = I
+              P = D( I )
+              DO 30 J = II, N
+                 IF( D( J ).LT.P ) THEN
+                    K = J
+                    P = D( J )
+                 END IF
+   30         CONTINUE
+              IF( K.NE.I ) THEN
+                 D( K ) = D( I )
+                 D( I ) = P
+                 CALL DSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
+              END IF
+   40      CONTINUE
          END IF
       END IF
 *

diff --git a/SRC/sstedc.f b/SRC/sstedc.f
index 841f7e4..f4e3d0b 100644 (file)
--- a/SRC/sstedc.f
+++ b/SRC/sstedc.f
@@ -442,38 +442,32 @@
 *
 *        endwhile
 *
-*        If the problem split any number of times, then the eigenvalues
-*        will not be properly ordered.  Here we permute the eigenvalues
-*        (and the associated eigenvectors) into ascending order.
+         IF( ICOMPZ.EQ.0 ) THEN
 *
-         IF( M.NE.N ) THEN
-            IF( ICOMPZ.EQ.0 ) THEN
+*          Use Quick Sort
 *
-*              Use Quick Sort
+           CALL SLASRT( 'I', N, D, INFO )
 *
-               CALL SLASRT( 'I', N, D, INFO )
-*
-            ELSE
+         ELSE
 *
-*              Use Selection Sort to minimize swaps of eigenvectors
-*
-               DO 40 II = 2, N
-                  I = II - 1
-                  K = I
-                  P = D( I )
-                  DO 30 J = II, N
-                     IF( D( J ).LT.P ) THEN
-                        K = J
-                        P = D( J )
-                     END IF
-   30             CONTINUE
-                  IF( K.NE.I ) THEN
-                     D( K ) = D( I )
-                     D( I ) = P
-                     CALL SSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
-                  END IF
-   40          CONTINUE
-            END IF
+*          Use Selection Sort to minimize swaps of eigenvectors
+*
+           DO 40 II = 2, N
+              I = II - 1
+              K = I
+              P = D( I )
+              DO 30 J = II, N
+                 IF( D( J ).LT.P ) THEN
+                    K = J
+                    P = D( J )
+                 END IF
+   30         CONTINUE
+              IF( K.NE.I ) THEN
+                 D( K ) = D( I )
+                 D( I ) = P
+                 CALL SSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
+              END IF
+   40      CONTINUE
          END IF
       END IF
 *

diff --git a/SRC/zstedc.f b/SRC/zstedc.f
index c0b1edd..37ef718 100644 (file)
--- a/SRC/zstedc.f
+++ b/SRC/zstedc.f
@@ -454,31 +454,25 @@
 *
 *        endwhile
 *
-*        If the problem split any number of times, then the eigenvalues
-*        will not be properly ordered.  Here we permute the eigenvalues
-*        (and the associated eigenvectors) into ascending order.
-*
-         IF( M.NE.N ) THEN
-*
-*           Use Selection Sort to minimize swaps of eigenvectors
-*
-            DO 60 II = 2, N
-               I = II - 1
-               K = I
-               P = D( I )
-               DO 50 J = II, N
-                  IF( D( J ).LT.P ) THEN
-                     K = J
-                     P = D( J )
-                  END IF
-   50          CONTINUE
-               IF( K.NE.I ) THEN
-                  D( K ) = D( I )
-                  D( I ) = P
-                  CALL ZSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
-               END IF
-   60       CONTINUE
-         END IF
+*
+*        Use Selection Sort to minimize swaps of eigenvectors
+*
+         DO 60 II = 2, N
+           I = II - 1
+           K = I
+           P = D( I )
+           DO 50 J = II, N
+              IF( D( J ).LT.P ) THEN
+                 K = J
+                 P = D( J )
+              END IF
+   50      CONTINUE
+           IF( K.NE.I ) THEN
+              D( K ) = D( I )
+              D( I ) = P
+              CALL ZSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
+           END IF
+   60    CONTINUE
       END IF
 *
    70 CONTINUE