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C DLANST    SOURCE    BP208322  18/07/10    21:15:11     9872           *> \brief \b DLANST returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric tridiagonal matrix.**  =========== DOCUMENTATION ===========** Online html documentation available at*            http://www.netlib.org/lapack/explore-html/**> \htmlonly*> Download DLANST + dependencies*> &lt;a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlanst.f">*> [TGZ]&lt;/a>*> &lt;a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlanst.f">*> [ZIP]&lt;/a>*> &lt;a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlanst.f">*> [TXT]&lt;/a>*> \endhtmlonly**  Definition:*  ===========**       REAL*8 FUNCTION DLANST( NORM, N, D, E )**       .. Scalar Arguments ..*       CHARACTER          NORM*       INTEGER            N*       ..*       .. Array Arguments ..*       REAL*8   D( * ), E( * )*       ..***> \par Purpose:*  =============*>*> \verbatim*>*> 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.*> \endverbatim*>*> \return DLANST*> \verbatim*>*>    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.*> \endverbatim**  Arguments:*  ==========**> \param[in] NORM*> \verbatim*>          NORM is CHARACTER*1*>          Specifies the value to be returned in DLANST as described*>          above.*> \endverbatim*>*> \param[in] N*> \verbatim*>          N is INTEGER*>          The order of the matrix A.  N >= 0.  When N = 0, DLANST is*>          set to zero.*> \endverbatim*>*> \param[in] D*> \verbatim*>          D is DOUBLE PRECISION array, dimension (N)*>          The diagonal elements of A.*> \endverbatim*>*> \param[in] E*> \verbatim*>          E is DOUBLE PRECISION array, dimension (N-1)*>          The (n-1) sub-diagonal or super-diagonal elements of A.*> \endverbatim**  Authors:*  ========**> \author Univ. of Tennessee*> \author Univ. of California Berkeley*> \author Univ. of Colorado Denver*> \author NAG Ltd.**> \date December 2016**> \ingroup OTHERauxiliary**  =====================================================================      FUNCTION DLANST( NORM, N, D, E )**  -- LAPACK auxiliary routine (version 3.7.0) --*  -- LAPACK is a software package provided by Univ. of Tennessee,    --*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--*     December 2016**     .. Scalar Arguments ..      REAL*8             DLANST      CHARACTER          NORM      INTEGER            N*     ..*     .. Array Arguments ..      REAL*8   D( * ), E( * )*     ..**  =====================================================================**     .. Parameters ..      REAL*8   ONE, ZERO      PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )*     ..*     .. Local Scalars ..      INTEGER            I      REAL*8   ANORM, SCALE, SUM*     ..*     .. External Functions ..      LOGICAL            LSAME, DISNAN      EXTERNAL           LSAME, DISNAN*     ..*     .. External Subroutines ..      EXTERNAL           DLASSQ*     ..**     .. Intrinsic Functions ..*      INTRINSIC          ABS, 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            SUM = ABS( D( I ) )            IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM            SUM = ABS( E( I ) )            IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM   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 = ABS( D( 1 ) )+ABS( E( 1 ) )            SUM = ABS( E( N-1 ) )+ABS( D( N ) )            IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM            DO 20 I = 2, N - 1               SUM = ABS( D( I ) )+ABS( E( I ) )+ABS( E( I-1 ) )               IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM   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

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