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OpenBLAS/lapack-netlib/SRC/sla_gercond.f

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*> \brief \b SLA_GERCOND estimates the Skeel condition number for a general matrix.
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download SLA_GERCOND + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/sla_gercond.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/sla_gercond.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/sla_gercond.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* REAL FUNCTION SLA_GERCOND ( TRANS, N, A, LDA, AF, LDAF, IPIV,
* CMODE, C, INFO, WORK, IWORK )
*
* .. Scalar Arguments ..
* CHARACTER TRANS
* INTEGER N, LDA, LDAF, INFO, CMODE
* ..
* .. Array Arguments ..
* INTEGER IPIV( * ), IWORK( * )
* REAL A( LDA, * ), AF( LDAF, * ), WORK( * ),
* $ C( * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> SLA_GERCOND estimates the Skeel condition number of op(A) * op2(C)
*> where op2 is determined by CMODE as follows
*> CMODE = 1 op2(C) = C
*> CMODE = 0 op2(C) = I
*> CMODE = -1 op2(C) = inv(C)
*> The Skeel condition number cond(A) = norminf( |inv(A)||A| )
*> is computed by computing scaling factors R such that
*> diag(R)*A*op2(C) is row equilibrated and computing the standard
*> infinity-norm condition number.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] TRANS
*> \verbatim
*> TRANS is CHARACTER*1
*> Specifies the form of the system of equations:
*> = 'N': A * X = B (No transpose)
*> = 'T': A**T * X = B (Transpose)
*> = 'C': A**H * X = B (Conjugate Transpose = Transpose)
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The number of linear equations, i.e., the order of the
*> matrix A. N >= 0.
*> \endverbatim
*>
*> \param[in] A
*> \verbatim
*> A is REAL array, dimension (LDA,N)
*> On entry, the N-by-N matrix A.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*> LDA is INTEGER
*> The leading dimension of the array A. LDA >= max(1,N).
*> \endverbatim
*>
*> \param[in] AF
*> \verbatim
*> AF is REAL array, dimension (LDAF,N)
*> The factors L and U from the factorization
*> A = P*L*U as computed by SGETRF.
*> \endverbatim
*>
*> \param[in] LDAF
*> \verbatim
*> LDAF is INTEGER
*> The leading dimension of the array AF. LDAF >= max(1,N).
*> \endverbatim
*>
*> \param[in] IPIV
*> \verbatim
*> IPIV is INTEGER array, dimension (N)
*> The pivot indices from the factorization A = P*L*U
*> as computed by SGETRF; row i of the matrix was interchanged
*> with row IPIV(i).
*> \endverbatim
*>
*> \param[in] CMODE
*> \verbatim
*> CMODE is INTEGER
*> Determines op2(C) in the formula op(A) * op2(C) as follows:
*> CMODE = 1 op2(C) = C
*> CMODE = 0 op2(C) = I
*> CMODE = -1 op2(C) = inv(C)
*> \endverbatim
*>
*> \param[in] C
*> \verbatim
*> C is REAL array, dimension (N)
*> The vector C in the formula op(A) * op2(C).
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*> INFO is INTEGER
*> = 0: Successful exit.
*> i > 0: The ith argument is invalid.
*> \endverbatim
*>
*> \param[in] WORK
*> \verbatim
*> WORK is REAL array, dimension (3*N).
*> Workspace.
*> \endverbatim
*>
*> \param[in] IWORK
*> \verbatim
*> IWORK is INTEGER array, dimension (N).
*> Workspace.2
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date September 2012
*
*> \ingroup realGEcomputational
*
* =====================================================================
REAL FUNCTION SLA_GERCOND ( TRANS, N, A, LDA, AF, LDAF, IPIV,
$ CMODE, C, INFO, WORK, IWORK )
*
* -- LAPACK computational routine (version 3.4.2) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* September 2012
*
* .. Scalar Arguments ..
CHARACTER TRANS
INTEGER N, LDA, LDAF, INFO, CMODE
* ..
* .. Array Arguments ..
INTEGER IPIV( * ), IWORK( * )
REAL A( LDA, * ), AF( LDAF, * ), WORK( * ),
$ C( * )
* ..
*
* =====================================================================
*
* .. Local Scalars ..
LOGICAL NOTRANS
INTEGER KASE, I, J
REAL AINVNM, TMP
* ..
* .. Local Arrays ..
INTEGER ISAVE( 3 )
* ..
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. External Subroutines ..
EXTERNAL SLACN2, SGETRS, XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, MAX
* ..
* .. Executable Statements ..
*
SLA_GERCOND = 0.0
*
INFO = 0
NOTRANS = LSAME( TRANS, 'N' )
IF ( .NOT. NOTRANS .AND. .NOT. LSAME(TRANS, 'T')
$ .AND. .NOT. LSAME(TRANS, 'C') ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -4
ELSE IF( LDAF.LT.MAX( 1, N ) ) THEN
INFO = -6
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'SLA_GERCOND', -INFO )
RETURN
END IF
IF( N.EQ.0 ) THEN
SLA_GERCOND = 1.0
RETURN
END IF
*
* Compute the equilibration matrix R such that
* inv(R)*A*C has unit 1-norm.
*
IF (NOTRANS) THEN
DO I = 1, N
TMP = 0.0
IF ( CMODE .EQ. 1 ) THEN
DO J = 1, N
TMP = TMP + ABS( A( I, J ) * C( J ) )
END DO
ELSE IF ( CMODE .EQ. 0 ) THEN
DO J = 1, N
TMP = TMP + ABS( A( I, J ) )
END DO
ELSE
DO J = 1, N
TMP = TMP + ABS( A( I, J ) / C( J ) )
END DO
END IF
WORK( 2*N+I ) = TMP
END DO
ELSE
DO I = 1, N
TMP = 0.0
IF ( CMODE .EQ. 1 ) THEN
DO J = 1, N
TMP = TMP + ABS( A( J, I ) * C( J ) )
END DO
ELSE IF ( CMODE .EQ. 0 ) THEN
DO J = 1, N
TMP = TMP + ABS( A( J, I ) )
END DO
ELSE
DO J = 1, N
TMP = TMP + ABS( A( J, I ) / C( J ) )
END DO
END IF
WORK( 2*N+I ) = TMP
END DO
END IF
*
* Estimate the norm of inv(op(A)).
*
AINVNM = 0.0
KASE = 0
10 CONTINUE
CALL SLACN2( N, WORK( N+1 ), WORK, IWORK, AINVNM, KASE, ISAVE )
IF( KASE.NE.0 ) THEN
IF( KASE.EQ.2 ) THEN
*
* Multiply by R.
*
DO I = 1, N
WORK(I) = WORK(I) * WORK(2*N+I)
END DO
IF (NOTRANS) THEN
CALL SGETRS( 'No transpose', N, 1, AF, LDAF, IPIV,
$ WORK, N, INFO )
ELSE
CALL SGETRS( 'Transpose', N, 1, AF, LDAF, IPIV,
$ WORK, N, INFO )
END IF
*
* Multiply by inv(C).
*
IF ( CMODE .EQ. 1 ) THEN
DO I = 1, N
WORK( I ) = WORK( I ) / C( I )
END DO
ELSE IF ( CMODE .EQ. -1 ) THEN
DO I = 1, N
WORK( I ) = WORK( I ) * C( I )
END DO
END IF
ELSE
*
* Multiply by inv(C**T).
*
IF ( CMODE .EQ. 1 ) THEN
DO I = 1, N
WORK( I ) = WORK( I ) / C( I )
END DO
ELSE IF ( CMODE .EQ. -1 ) THEN
DO I = 1, N
WORK( I ) = WORK( I ) * C( I )
END DO
END IF
IF (NOTRANS) THEN
CALL SGETRS( 'Transpose', N, 1, AF, LDAF, IPIV,
$ WORK, N, INFO )
ELSE
CALL SGETRS( 'No transpose', N, 1, AF, LDAF, IPIV,
$ WORK, N, INFO )
END IF
*
* Multiply by R.
*
DO I = 1, N
WORK( I ) = WORK( I ) * WORK( 2*N+I )
END DO
END IF
GO TO 10
END IF
*
* Compute the estimate of the reciprocal condition number.
*
IF( AINVNM .NE. 0.0 )
$ SLA_GERCOND = ( 1.0 / AINVNM )
*
RETURN
*
END
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