*> \brief \b CGECON * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download CGECON + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE CGECON( NORM, N, A, LDA, ANORM, RCOND, WORK, RWORK, * INFO ) * * .. Scalar Arguments .. * CHARACTER NORM * INTEGER INFO, LDA, N * REAL ANORM, RCOND * .. * .. Array Arguments .. * REAL RWORK( * ) * COMPLEX A( LDA, * ), WORK( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> CGECON estimates the reciprocal of the condition number of a general *> complex matrix A, in either the 1-norm or the infinity-norm, using *> the LU factorization computed by CGETRF. *> *> 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] A *> \verbatim *> A is COMPLEX array, dimension (LDA,N) *> The factors L and U from the factorization A = P*L*U *> as computed by CGETRF. *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> The leading dimension of the array A. LDA >= max(1,N). *> \endverbatim *> *> \param[in] ANORM *> \verbatim *> ANORM is REAL *> 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 REAL *> 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 array, dimension (2*N) *> \endverbatim *> *> \param[out] RWORK *> \verbatim *> RWORK is REAL array, dimension (2*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 complexGEcomputational * * ===================================================================== SUBROUTINE CGECON( NORM, N, A, LDA, 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, LDA, N REAL ANORM, RCOND * .. * .. Array Arguments .. REAL RWORK( * ) COMPLEX A( LDA, * ), WORK( * ) * .. * * ===================================================================== * * .. Parameters .. REAL ONE, ZERO PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) * .. * .. Local Scalars .. LOGICAL ONENRM CHARACTER NORMIN INTEGER IX, KASE, KASE1 REAL AINVNM, SCALE, SL, SMLNUM, SU COMPLEX ZDUM * .. * .. Local Arrays .. INTEGER ISAVE( 3 ) * .. * .. External Functions .. LOGICAL LSAME INTEGER ICAMAX REAL SLAMCH EXTERNAL LSAME, ICAMAX, SLAMCH * .. * .. External Subroutines .. EXTERNAL CLACN2, CLATRS, CSRSCL, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC ABS, AIMAG, MAX, REAL * .. * .. Statement Functions .. REAL CABS1 * .. * .. Statement Function definitions .. CABS1( ZDUM ) = ABS( REAL( ZDUM ) ) + ABS( AIMAG( 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( LDA.LT.MAX( 1, N ) ) THEN INFO = -4 ELSE IF( ANORM.LT.ZERO ) THEN INFO = -5 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'CGECON', -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 = SLAMCH( 'Safe minimum' ) * * Estimate the norm of inv(A). * AINVNM = ZERO NORMIN = 'N' IF( ONENRM ) THEN KASE1 = 1 ELSE KASE1 = 2 END IF KASE = 0 10 CONTINUE CALL CLACN2( N, WORK( N+1 ), WORK, AINVNM, KASE, ISAVE ) IF( KASE.NE.0 ) THEN IF( KASE.EQ.KASE1 ) THEN * * Multiply by inv(L). * CALL CLATRS( 'Lower', 'No transpose', 'Unit', NORMIN, N, A, $ LDA, WORK, SL, RWORK, INFO ) * * Multiply by inv(U). * CALL CLATRS( 'Upper', 'No transpose', 'Non-unit', NORMIN, N, $ A, LDA, WORK, SU, RWORK( N+1 ), INFO ) ELSE * * Multiply by inv(U**H). * CALL CLATRS( 'Upper', 'Conjugate transpose', 'Non-unit', $ NORMIN, N, A, LDA, WORK, SU, RWORK( N+1 ), $ INFO ) * * Multiply by inv(L**H). * CALL CLATRS( 'Lower', 'Conjugate transpose', 'Unit', NORMIN, $ N, A, LDA, WORK, SL, RWORK, INFO ) END IF * * Divide X by 1/(SL*SU) if doing so will not cause overflow. * SCALE = SL*SU NORMIN = 'Y' IF( SCALE.NE.ONE ) THEN IX = ICAMAX( N, WORK, 1 ) IF( SCALE.LT.CABS1( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO ) $ GO TO 20 CALL CSRSCL( 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 * 20 CONTINUE RETURN * * End of CGECON * END