*> \brief \b ZGBCON * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download ZGBCON + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE ZGBCON( NORM, N, KL, KU, AB, LDAB, IPIV, ANORM, RCOND, * WORK, RWORK, INFO ) * * .. Scalar Arguments .. * CHARACTER NORM * INTEGER INFO, KL, KU, LDAB, N * DOUBLE PRECISION ANORM, RCOND * .. * .. Array Arguments .. * INTEGER IPIV( * ) * DOUBLE PRECISION RWORK( * ) * COMPLEX*16 AB( LDAB, * ), WORK( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> ZGBCON estimates the reciprocal of the condition number of a complex *> general band matrix A, in either the 1-norm or the infinity-norm, *> using the LU factorization computed by ZGBTRF. *> *> An estimate is obtained for norm(inv(A)), and the reciprocal of the *> condition number is computed as *> RCOND = 1 / ( norm(A) * norm(inv(A)) ). *> \endverbatim * * Arguments: * ========== * *> \param[in] NORM *> \verbatim *> NORM is CHARACTER*1 *> Specifies whether the 1-norm condition number or the *> infinity-norm condition number is required: *> = '1' or 'O': 1-norm; *> = 'I': Infinity-norm. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The order of the matrix A. N >= 0. *> \endverbatim *> *> \param[in] KL *> \verbatim *> KL is INTEGER *> The number of subdiagonals within the band of A. KL >= 0. *> \endverbatim *> *> \param[in] KU *> \verbatim *> KU is INTEGER *> The number of superdiagonals within the band of A. KU >= 0. *> \endverbatim *> *> \param[in] AB *> \verbatim *> AB is COMPLEX*16 array, dimension (LDAB,N) *> Details of the LU factorization of the band matrix A, as *> computed by ZGBTRF. U is stored as an upper triangular band *> matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and *> the multipliers used during the factorization are stored in *> rows KL+KU+2 to 2*KL+KU+1. *> \endverbatim *> *> \param[in] LDAB *> \verbatim *> LDAB is INTEGER *> The leading dimension of the array AB. LDAB >= 2*KL+KU+1. *> \endverbatim *> *> \param[in] IPIV *> \verbatim *> IPIV is INTEGER array, dimension (N) *> The pivot indices; for 1 <= i <= N, row i of the matrix was *> interchanged with row IPIV(i). *> \endverbatim *> *> \param[in] ANORM *> \verbatim *> ANORM is DOUBLE PRECISION *> If NORM = '1' or 'O', the 1-norm of the original matrix A. *> If NORM = 'I', the infinity-norm of the original matrix A. *> \endverbatim *> *> \param[out] RCOND *> \verbatim *> RCOND is DOUBLE PRECISION *> The reciprocal of the condition number of the matrix A, *> computed as RCOND = 1/(norm(A) * norm(inv(A))). *> \endverbatim *> *> \param[out] WORK *> \verbatim *> WORK is COMPLEX*16 array, dimension (2*N) *> \endverbatim *> *> \param[out] RWORK *> \verbatim *> RWORK is DOUBLE PRECISION array, dimension (N) *> \endverbatim *> *> \param[out] INFO *> \verbatim *> INFO is INTEGER *> = 0: successful exit *> < 0: if INFO = -i, the i-th argument had an illegal value *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup complex16GBcomputational * * ===================================================================== SUBROUTINE ZGBCON( NORM, N, KL, KU, AB, LDAB, IPIV, ANORM, RCOND, \$ WORK, RWORK, INFO ) * * -- LAPACK computational routine -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * * .. Scalar Arguments .. CHARACTER NORM INTEGER INFO, KL, KU, LDAB, N DOUBLE PRECISION ANORM, RCOND * .. * .. Array Arguments .. INTEGER IPIV( * ) DOUBLE PRECISION RWORK( * ) COMPLEX*16 AB( LDAB, * ), WORK( * ) * .. * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ONE, ZERO PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) * .. * .. Local Scalars .. LOGICAL LNOTI, ONENRM CHARACTER NORMIN INTEGER IX, J, JP, KASE, KASE1, KD, LM DOUBLE PRECISION AINVNM, SCALE, SMLNUM COMPLEX*16 T, ZDUM * .. * .. Local Arrays .. INTEGER ISAVE( 3 ) * .. * .. External Functions .. LOGICAL LSAME INTEGER IZAMAX DOUBLE PRECISION DLAMCH COMPLEX*16 ZDOTC EXTERNAL LSAME, IZAMAX, DLAMCH, ZDOTC * .. * .. External Subroutines .. EXTERNAL XERBLA, ZAXPY, ZDRSCL, ZLACN2, ZLATBS * .. * .. Intrinsic Functions .. INTRINSIC ABS, DBLE, DIMAG, MIN * .. * .. Statement Functions .. DOUBLE PRECISION CABS1 * .. * .. Statement Function definitions .. CABS1( ZDUM ) = ABS( DBLE( ZDUM ) ) + ABS( DIMAG( ZDUM ) ) * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 ONENRM = NORM.EQ.'1' .OR. LSAME( NORM, 'O' ) IF( .NOT.ONENRM .AND. .NOT.LSAME( NORM, 'I' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( KL.LT.0 ) THEN INFO = -3 ELSE IF( KU.LT.0 ) THEN INFO = -4 ELSE IF( LDAB.LT.2*KL+KU+1 ) THEN INFO = -6 ELSE IF( ANORM.LT.ZERO ) THEN INFO = -8 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'ZGBCON', -INFO ) RETURN END IF * * Quick return if possible * RCOND = ZERO IF( N.EQ.0 ) THEN RCOND = ONE RETURN ELSE IF( ANORM.EQ.ZERO ) THEN RETURN END IF * SMLNUM = DLAMCH( 'Safe minimum' ) * * Estimate the norm of inv(A). * AINVNM = ZERO NORMIN = 'N' IF( ONENRM ) THEN KASE1 = 1 ELSE KASE1 = 2 END IF KD = KL + KU + 1 LNOTI = KL.GT.0 KASE = 0 10 CONTINUE CALL ZLACN2( N, WORK( N+1 ), WORK, AINVNM, KASE, ISAVE ) IF( KASE.NE.0 ) THEN IF( KASE.EQ.KASE1 ) THEN * * Multiply by inv(L). * IF( LNOTI ) THEN DO 20 J = 1, N - 1 LM = MIN( KL, N-J ) JP = IPIV( J ) T = WORK( JP ) IF( JP.NE.J ) THEN WORK( JP ) = WORK( J ) WORK( J ) = T END IF CALL ZAXPY( LM, -T, AB( KD+1, J ), 1, WORK( J+1 ), 1 ) 20 CONTINUE END IF * * Multiply by inv(U). * CALL ZLATBS( 'Upper', 'No transpose', 'Non-unit', NORMIN, N, \$ KL+KU, AB, LDAB, WORK, SCALE, RWORK, INFO ) ELSE * * Multiply by inv(U**H). * CALL ZLATBS( 'Upper', 'Conjugate transpose', 'Non-unit', \$ NORMIN, N, KL+KU, AB, LDAB, WORK, SCALE, RWORK, \$ INFO ) * * Multiply by inv(L**H). * IF( LNOTI ) THEN DO 30 J = N - 1, 1, -1 LM = MIN( KL, N-J ) WORK( J ) = WORK( J ) - ZDOTC( LM, AB( KD+1, J ), 1, \$ WORK( J+1 ), 1 ) JP = IPIV( J ) IF( JP.NE.J ) THEN T = WORK( JP ) WORK( JP ) = WORK( J ) WORK( J ) = T END IF 30 CONTINUE END IF END IF * * Divide X by 1/SCALE if doing so will not cause overflow. * NORMIN = 'Y' IF( SCALE.NE.ONE ) THEN IX = IZAMAX( N, WORK, 1 ) IF( SCALE.LT.CABS1( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO ) \$ GO TO 40 CALL ZDRSCL( N, SCALE, WORK, 1 ) END IF GO TO 10 END IF * * Compute the estimate of the reciprocal condition number. * IF( AINVNM.NE.ZERO ) \$ RCOND = ( ONE / AINVNM ) / ANORM * 40 CONTINUE RETURN * * End of ZGBCON * END