184 lines
5.1 KiB
Fortran
184 lines
5.1 KiB
Fortran
*> \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.
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download DLANST + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlanst.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlanst.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlanst.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* DOUBLE PRECISION FUNCTION DLANST( NORM, N, D, E )
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*
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* .. Scalar Arguments ..
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* CHARACTER NORM
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* INTEGER N
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION D( * ), E( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DLANST returns the value of the one norm, or the Frobenius norm, or
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*> the infinity norm, or the element of largest absolute value of a
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*> real symmetric tridiagonal matrix A.
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*> \endverbatim
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*>
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*> \return DLANST
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*> \verbatim
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*>
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*> DLANST = ( max(abs(A(i,j))), NORM = 'M' or 'm'
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*> (
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*> ( norm1(A), NORM = '1', 'O' or 'o'
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*> (
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*> ( normI(A), NORM = 'I' or 'i'
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*> (
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*> ( normF(A), NORM = 'F', 'f', 'E' or 'e'
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*>
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*> where norm1 denotes the one norm of a matrix (maximum column sum),
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*> normI denotes the infinity norm of a matrix (maximum row sum) and
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*> normF denotes the Frobenius norm of a matrix (square root of sum of
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*> squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] NORM
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*> \verbatim
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*> NORM is CHARACTER*1
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*> Specifies the value to be returned in DLANST as described
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*> above.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The order of the matrix A. N >= 0. When N = 0, DLANST is
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*> set to zero.
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*> \endverbatim
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*>
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*> \param[in] D
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*> \verbatim
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*> D is DOUBLE PRECISION array, dimension (N)
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*> The diagonal elements of A.
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*> \endverbatim
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*>
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*> \param[in] E
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*> \verbatim
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*> E is DOUBLE PRECISION array, dimension (N-1)
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*> The (n-1) sub-diagonal or super-diagonal elements of A.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup OTHERauxiliary
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*
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* =====================================================================
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DOUBLE PRECISION FUNCTION DLANST( NORM, N, D, E )
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*
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* -- LAPACK auxiliary routine --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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CHARACTER NORM
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INTEGER N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION D( * ), E( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ONE, ZERO
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PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
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* ..
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* .. Local Scalars ..
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INTEGER I
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DOUBLE PRECISION ANORM, SCALE, SUM
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* ..
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* .. External Functions ..
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LOGICAL LSAME, DISNAN
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EXTERNAL LSAME, DISNAN
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* ..
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* .. External Subroutines ..
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EXTERNAL DLASSQ
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, SQRT
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* ..
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* .. Executable Statements ..
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*
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IF( N.LE.0 ) THEN
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ANORM = ZERO
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ELSE IF( LSAME( NORM, 'M' ) ) THEN
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*
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* Find max(abs(A(i,j))).
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*
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ANORM = ABS( D( N ) )
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DO 10 I = 1, N - 1
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SUM = ABS( D( I ) )
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IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM
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SUM = ABS( E( I ) )
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IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM
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10 CONTINUE
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ELSE IF( LSAME( NORM, 'O' ) .OR. NORM.EQ.'1' .OR.
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$ LSAME( NORM, 'I' ) ) THEN
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*
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* Find norm1(A).
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*
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IF( N.EQ.1 ) THEN
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ANORM = ABS( D( 1 ) )
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ELSE
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ANORM = ABS( D( 1 ) )+ABS( E( 1 ) )
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SUM = ABS( E( N-1 ) )+ABS( D( N ) )
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IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM
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DO 20 I = 2, N - 1
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SUM = ABS( D( I ) )+ABS( E( I ) )+ABS( E( I-1 ) )
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IF( ANORM .LT. SUM .OR. DISNAN( SUM ) ) ANORM = SUM
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20 CONTINUE
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END IF
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ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
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*
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* Find normF(A).
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*
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SCALE = ZERO
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SUM = ONE
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IF( N.GT.1 ) THEN
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CALL DLASSQ( N-1, E, 1, SCALE, SUM )
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SUM = 2*SUM
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END IF
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CALL DLASSQ( N, D, 1, SCALE, SUM )
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ANORM = SCALE*SQRT( SUM )
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END IF
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*
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DLANST = ANORM
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RETURN
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*
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* End of DLANST
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*
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END
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