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+      DOUBLE PRECISION FUNCTION DLANST( NORM, N, D, E )
+*
+*  -- LAPACK auxiliary routine (version 3.1) --
+*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
+*     November 2006
+*
+*     .. Scalar Arguments ..
+      CHARACTER          NORM
+      INTEGER            N
+*     ..
+*     .. Array Arguments ..
+      DOUBLE PRECISION   D( * ), E( * )
+*     ..
+*
+*  Purpose
+*  =======
+*
+*  DLANST  returns the value of the one norm,  or the Frobenius norm, or
+*  the  infinity norm,  or the  element of  largest absolute value  of a
+*  real symmetric tridiagonal matrix A.
+*
+*  Description
+*  ===========
+*
+*  DLANST returns the value
+*
+*     DLANST = ( max(abs(A(i,j))), NORM = 'M' or 'm'
+*              (
+*              ( norm1(A),         NORM = '1', 'O' or 'o'
+*              (
+*              ( normI(A),         NORM = 'I' or 'i'
+*              (
+*              ( normF(A),         NORM = 'F', 'f', 'E' or 'e'
+*
+*  where  norm1  denotes the  one norm of a matrix (maximum column sum),
+*  normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
+*  normF  denotes the  Frobenius norm of a matrix (square root of sum of
+*  squares).  Note that  max(abs(A(i,j)))  is not a consistent matrix norm.
+*
+*  Arguments
+*  =========
+*
+*  NORM    (input) CHARACTER*1
+*          Specifies the value to be returned in DLANST as described
+*          above.
+*
+*  N       (input) INTEGER
+*          The order of the matrix A.  N >= 0.  When N = 0, DLANST is
+*          set to zero.
+*
+*  D       (input) DOUBLE PRECISION array, dimension (N)
+*          The diagonal elements of A.
+*
+*  E       (input) DOUBLE PRECISION array, dimension (N-1)
+*          The (n-1) sub-diagonal or super-diagonal elements of A.
+*
+*  =====================================================================
+*
+*     .. Parameters ..
+      DOUBLE PRECISION   ONE, ZERO
+      PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
+*     ..
+*     .. Local Scalars ..
+      INTEGER            I
+      DOUBLE PRECISION   ANORM, SCALE, SUM
+*     ..
+*     .. External Functions ..
+      LOGICAL            LSAME
+      EXTERNAL           LSAME
+*     ..
+*     .. External Subroutines ..
+      EXTERNAL           DLASSQ
+*     ..
+*     .. Intrinsic Functions ..
+      INTRINSIC          ABS, MAX, SQRT
+*     ..
+*     .. Executable Statements ..
+*
+      IF( N.LE.0 ) THEN
+         ANORM = ZERO
+      ELSE IF( LSAME( NORM, 'M' ) ) THEN
+*
+*        Find max(abs(A(i,j))).
+*
+         ANORM = ABS( D( N ) )
+         DO 10 I = 1, N - 1
+            ANORM = MAX( ANORM, ABS( D( I ) ) )
+            ANORM = MAX( ANORM, ABS( E( I ) ) )
+   10    CONTINUE
+      ELSE IF( LSAME( NORM, 'O' ) .OR. NORM.EQ.'1' .OR.
+     $         LSAME( NORM, 'I' ) ) THEN
+*
+*        Find norm1(A).
+*
+         IF( N.EQ.1 ) THEN
+            ANORM = ABS( D( 1 ) )
+         ELSE
+            ANORM = MAX( ABS( D( 1 ) )+ABS( E( 1 ) ),
+     $              ABS( E( N-1 ) )+ABS( D( N ) ) )
+            DO 20 I = 2, N - 1
+               ANORM = MAX( ANORM, ABS( D( I ) )+ABS( E( I ) )+
+     $                 ABS( E( I-1 ) ) )
+   20       CONTINUE
+         END IF
+      ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
+*
+*        Find normF(A).
+*
+         SCALE = ZERO
+         SUM = ONE
+         IF( N.GT.1 ) THEN
+            CALL DLASSQ( N-1, E, 1, SCALE, SUM )
+            SUM = 2*SUM
+         END IF
+         CALL DLASSQ( N, D, 1, SCALE, SUM )
+         ANORM = SCALE*SQRT( SUM )
+      END IF
+*
+      DLANST = ANORM
+      RETURN
+*
+*     End of DLANST
+*
+      END