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OpenBLAS/lapack-netlib/SRC/clansb.f

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*> \brief \b CLANSB returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a symmetric band matrix.
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download CLANSB + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/clansb.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/clansb.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/clansb.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* REAL FUNCTION CLANSB( NORM, UPLO, N, K, AB, LDAB,
* WORK )
*
* .. Scalar Arguments ..
* CHARACTER NORM, UPLO
* INTEGER K, LDAB, N
* ..
* .. Array Arguments ..
* REAL WORK( * )
* COMPLEX AB( LDAB, * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> CLANSB returns the value of the one norm, or the Frobenius norm, or
*> the infinity norm, or the element of largest absolute value of an
*> n by n symmetric band matrix A, with k super-diagonals.
*> \endverbatim
*>
*> \return CLANSB
*> \verbatim
*>
*> CLANSB = ( 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 CLANSB as described
*> above.
*> \endverbatim
*>
*> \param[in] UPLO
*> \verbatim
*> UPLO is CHARACTER*1
*> Specifies whether the upper or lower triangular part of the
*> band matrix A is supplied.
*> = 'U': Upper triangular part is supplied
*> = 'L': Lower triangular part is supplied
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The order of the matrix A. N >= 0. When N = 0, CLANSB is
*> set to zero.
*> \endverbatim
*>
*> \param[in] K
*> \verbatim
*> K is INTEGER
*> The number of super-diagonals or sub-diagonals of the
*> band matrix A. K >= 0.
*> \endverbatim
*>
*> \param[in] AB
*> \verbatim
*> AB is COMPLEX array, dimension (LDAB,N)
*> The upper or lower triangle of the symmetric band matrix A,
*> stored in the first K+1 rows of AB. The j-th column of A is
*> stored in the j-th column of the array AB as follows:
*> if UPLO = 'U', AB(k+1+i-j,j) = A(i,j) for max(1,j-k)<=i<=j;
*> if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+k).
*> \endverbatim
*>
*> \param[in] LDAB
*> \verbatim
*> LDAB is INTEGER
*> The leading dimension of the array AB. LDAB >= K+1.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*> WORK is REAL array, dimension (MAX(1,LWORK)),
*> where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise,
*> WORK is not referenced.
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup complexOTHERauxiliary
*
* =====================================================================
REAL FUNCTION CLANSB( NORM, UPLO, N, K, AB, LDAB,
$ WORK )
*
* -- 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
*
IMPLICIT NONE
* .. Scalar Arguments ..
CHARACTER NORM, UPLO
INTEGER K, LDAB, N
* ..
* .. Array Arguments ..
REAL WORK( * )
COMPLEX AB( LDAB, * )
* ..
*
* =====================================================================
*
* .. Parameters ..
REAL ONE, ZERO
PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
* ..
* .. Local Scalars ..
INTEGER I, J, L
REAL ABSA, SUM, VALUE
* ..
* .. Local Arrays ..
REAL SSQ( 2 ), COLSSQ( 2 )
* ..
* .. External Functions ..
LOGICAL LSAME, SISNAN
EXTERNAL LSAME, SISNAN
* ..
* .. External Subroutines ..
EXTERNAL CLASSQ, SCOMBSSQ
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, MAX, MIN, SQRT
* ..
* .. Executable Statements ..
*
IF( N.EQ.0 ) THEN
VALUE = ZERO
ELSE IF( LSAME( NORM, 'M' ) ) THEN
*
* Find max(abs(A(i,j))).
*
VALUE = ZERO
IF( LSAME( UPLO, 'U' ) ) THEN
DO 20 J = 1, N
DO 10 I = MAX( K+2-J, 1 ), K + 1
SUM = ABS( AB( I, J ) )
IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
10 CONTINUE
20 CONTINUE
ELSE
DO 40 J = 1, N
DO 30 I = 1, MIN( N+1-J, K+1 )
SUM = ABS( AB( I, J ) )
IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
30 CONTINUE
40 CONTINUE
END IF
ELSE IF( ( LSAME( NORM, 'I' ) ) .OR. ( LSAME( NORM, 'O' ) ) .OR.
$ ( NORM.EQ.'1' ) ) THEN
*
* Find normI(A) ( = norm1(A), since A is symmetric).
*
VALUE = ZERO
IF( LSAME( UPLO, 'U' ) ) THEN
DO 60 J = 1, N
SUM = ZERO
L = K + 1 - J
DO 50 I = MAX( 1, J-K ), J - 1
ABSA = ABS( AB( L+I, J ) )
SUM = SUM + ABSA
WORK( I ) = WORK( I ) + ABSA
50 CONTINUE
WORK( J ) = SUM + ABS( AB( K+1, J ) )
60 CONTINUE
DO 70 I = 1, N
SUM = WORK( I )
IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
70 CONTINUE
ELSE
DO 80 I = 1, N
WORK( I ) = ZERO
80 CONTINUE
DO 100 J = 1, N
SUM = WORK( J ) + ABS( AB( 1, J ) )
L = 1 - J
DO 90 I = J + 1, MIN( N, J+K )
ABSA = ABS( AB( L+I, J ) )
SUM = SUM + ABSA
WORK( I ) = WORK( I ) + ABSA
90 CONTINUE
IF( VALUE .LT. SUM .OR. SISNAN( SUM ) ) VALUE = SUM
100 CONTINUE
END IF
ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
*
* Find normF(A).
* SSQ(1) is scale
* SSQ(2) is sum-of-squares
* For better accuracy, sum each column separately.
*
SSQ( 1 ) = ZERO
SSQ( 2 ) = ONE
*
* Sum off-diagonals
*
IF( K.GT.0 ) THEN
IF( LSAME( UPLO, 'U' ) ) THEN
DO 110 J = 2, N
COLSSQ( 1 ) = ZERO
COLSSQ( 2 ) = ONE
CALL CLASSQ( MIN( J-1, K ), AB( MAX( K+2-J, 1 ), J ),
$ 1, COLSSQ( 1 ), COLSSQ( 2 ) )
CALL SCOMBSSQ( SSQ, COLSSQ )
110 CONTINUE
L = K + 1
ELSE
DO 120 J = 1, N - 1
COLSSQ( 1 ) = ZERO
COLSSQ( 2 ) = ONE
CALL CLASSQ( MIN( N-J, K ), AB( 2, J ), 1,
$ COLSSQ( 1 ), COLSSQ( 2 ) )
CALL SCOMBSSQ( SSQ, COLSSQ )
120 CONTINUE
L = 1
END IF
SSQ( 2 ) = 2*SSQ( 2 )
ELSE
L = 1
END IF
*
* Sum diagonal
*
COLSSQ( 1 ) = ZERO
COLSSQ( 2 ) = ONE
CALL CLASSQ( N, AB( L, 1 ), LDAB, COLSSQ( 1 ), COLSSQ( 2 ) )
CALL SCOMBSSQ( SSQ, COLSSQ )
VALUE = SSQ( 1 )*SQRT( SSQ( 2 ) )
END IF
*
CLANSB = VALUE
RETURN
*
* End of CLANSB
*
END
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