380 lines
11 KiB
Fortran
380 lines
11 KiB
Fortran
*> \brief \b DSYTRI
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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 DSYTRI + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dsytri.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/dsytri.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/dsytri.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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* SUBROUTINE DSYTRI( UPLO, N, A, LDA, IPIV, WORK, INFO )
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*
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* .. Scalar Arguments ..
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* CHARACTER UPLO
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* INTEGER INFO, LDA, N
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* ..
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* .. Array Arguments ..
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* INTEGER IPIV( * )
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* DOUBLE PRECISION A( LDA, * ), WORK( * )
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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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*> DSYTRI computes the inverse of a real symmetric indefinite matrix
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*> A using the factorization A = U*D*U**T or A = L*D*L**T computed by
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*> DSYTRF.
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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] UPLO
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*> \verbatim
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*> UPLO is CHARACTER*1
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*> Specifies whether the details of the factorization are stored
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*> as an upper or lower triangular matrix.
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*> = 'U': Upper triangular, form is A = U*D*U**T;
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*> = 'L': Lower triangular, form is A = L*D*L**T.
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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.
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*> \endverbatim
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*>
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*> \param[in,out] A
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*> \verbatim
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*> A is DOUBLE PRECISION array, dimension (LDA,N)
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*> On entry, the block diagonal matrix D and the multipliers
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*> used to obtain the factor U or L as computed by DSYTRF.
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*>
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*> On exit, if INFO = 0, the (symmetric) inverse of the original
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*> matrix. If UPLO = 'U', the upper triangular part of the
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*> inverse is formed and the part of A below the diagonal is not
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*> referenced; if UPLO = 'L' the lower triangular part of the
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*> inverse is formed and the part of A above the diagonal is
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*> not referenced.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array A. LDA >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in] IPIV
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*> \verbatim
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*> IPIV is INTEGER array, dimension (N)
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*> Details of the interchanges and the block structure of D
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*> as determined by DSYTRF.
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*> \endverbatim
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*>
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*> \param[out] WORK
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*> \verbatim
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*> WORK is DOUBLE PRECISION array, dimension (N)
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*> \endverbatim
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*>
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*> \param[out] INFO
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*> \verbatim
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*> INFO is INTEGER
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*> = 0: successful exit
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*> < 0: if INFO = -i, the i-th argument had an illegal value
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*> > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its
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*> inverse could not be computed.
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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 doubleSYcomputational
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*
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* =====================================================================
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SUBROUTINE DSYTRI( UPLO, N, A, LDA, IPIV, WORK, INFO )
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*
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* -- LAPACK computational 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 UPLO
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INTEGER INFO, LDA, N
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* ..
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* .. Array Arguments ..
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INTEGER IPIV( * )
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DOUBLE PRECISION A( LDA, * ), WORK( * )
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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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LOGICAL UPPER
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INTEGER K, KP, KSTEP
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DOUBLE PRECISION AK, AKKP1, AKP1, D, T, TEMP
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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DOUBLE PRECISION DDOT
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EXTERNAL LSAME, DDOT
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* ..
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* .. External Subroutines ..
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EXTERNAL DCOPY, DSWAP, DSYMV, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, MAX
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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INFO = 0
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UPPER = LSAME( UPLO, 'U' )
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IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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INFO = -1
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ELSE IF( N.LT.0 ) THEN
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INFO = -2
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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -4
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'DSYTRI', -INFO )
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RETURN
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END IF
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*
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* Quick return if possible
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*
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IF( N.EQ.0 )
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$ RETURN
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*
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* Check that the diagonal matrix D is nonsingular.
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*
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IF( UPPER ) THEN
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*
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* Upper triangular storage: examine D from bottom to top
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*
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DO 10 INFO = N, 1, -1
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IF( IPIV( INFO ).GT.0 .AND. A( INFO, INFO ).EQ.ZERO )
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$ RETURN
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10 CONTINUE
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ELSE
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*
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* Lower triangular storage: examine D from top to bottom.
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*
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DO 20 INFO = 1, N
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IF( IPIV( INFO ).GT.0 .AND. A( INFO, INFO ).EQ.ZERO )
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$ RETURN
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20 CONTINUE
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END IF
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INFO = 0
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*
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IF( UPPER ) THEN
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*
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* Compute inv(A) from the factorization A = U*D*U**T.
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*
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* K is the main loop index, increasing from 1 to N in steps of
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* 1 or 2, depending on the size of the diagonal blocks.
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*
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K = 1
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30 CONTINUE
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*
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* If K > N, exit from loop.
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*
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IF( K.GT.N )
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$ GO TO 40
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*
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IF( IPIV( K ).GT.0 ) THEN
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*
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* 1 x 1 diagonal block
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*
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* Invert the diagonal block.
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*
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A( K, K ) = ONE / A( K, K )
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*
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* Compute column K of the inverse.
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*
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IF( K.GT.1 ) THEN
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CALL DCOPY( K-1, A( 1, K ), 1, WORK, 1 )
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CALL DSYMV( UPLO, K-1, -ONE, A, LDA, WORK, 1, ZERO,
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$ A( 1, K ), 1 )
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A( K, K ) = A( K, K ) - DDOT( K-1, WORK, 1, A( 1, K ),
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$ 1 )
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END IF
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KSTEP = 1
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ELSE
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*
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* 2 x 2 diagonal block
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*
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* Invert the diagonal block.
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*
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T = ABS( A( K, K+1 ) )
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AK = A( K, K ) / T
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AKP1 = A( K+1, K+1 ) / T
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AKKP1 = A( K, K+1 ) / T
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D = T*( AK*AKP1-ONE )
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A( K, K ) = AKP1 / D
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A( K+1, K+1 ) = AK / D
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A( K, K+1 ) = -AKKP1 / D
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*
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* Compute columns K and K+1 of the inverse.
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*
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IF( K.GT.1 ) THEN
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CALL DCOPY( K-1, A( 1, K ), 1, WORK, 1 )
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CALL DSYMV( UPLO, K-1, -ONE, A, LDA, WORK, 1, ZERO,
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$ A( 1, K ), 1 )
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A( K, K ) = A( K, K ) - DDOT( K-1, WORK, 1, A( 1, K ),
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$ 1 )
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A( K, K+1 ) = A( K, K+1 ) -
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$ DDOT( K-1, A( 1, K ), 1, A( 1, K+1 ), 1 )
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CALL DCOPY( K-1, A( 1, K+1 ), 1, WORK, 1 )
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CALL DSYMV( UPLO, K-1, -ONE, A, LDA, WORK, 1, ZERO,
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$ A( 1, K+1 ), 1 )
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A( K+1, K+1 ) = A( K+1, K+1 ) -
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$ DDOT( K-1, WORK, 1, A( 1, K+1 ), 1 )
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END IF
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KSTEP = 2
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END IF
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*
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KP = ABS( IPIV( K ) )
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IF( KP.NE.K ) THEN
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*
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* Interchange rows and columns K and KP in the leading
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* submatrix A(1:k+1,1:k+1)
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*
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CALL DSWAP( KP-1, A( 1, K ), 1, A( 1, KP ), 1 )
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CALL DSWAP( K-KP-1, A( KP+1, K ), 1, A( KP, KP+1 ), LDA )
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TEMP = A( K, K )
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A( K, K ) = A( KP, KP )
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A( KP, KP ) = TEMP
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IF( KSTEP.EQ.2 ) THEN
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TEMP = A( K, K+1 )
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A( K, K+1 ) = A( KP, K+1 )
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A( KP, K+1 ) = TEMP
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END IF
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END IF
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*
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K = K + KSTEP
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GO TO 30
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40 CONTINUE
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*
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ELSE
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*
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* Compute inv(A) from the factorization A = L*D*L**T.
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*
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* K is the main loop index, increasing from 1 to N in steps of
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* 1 or 2, depending on the size of the diagonal blocks.
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*
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K = N
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50 CONTINUE
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*
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* If K < 1, exit from loop.
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*
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IF( K.LT.1 )
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$ GO TO 60
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*
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IF( IPIV( K ).GT.0 ) THEN
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*
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* 1 x 1 diagonal block
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*
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* Invert the diagonal block.
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*
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A( K, K ) = ONE / A( K, K )
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*
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* Compute column K of the inverse.
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*
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IF( K.LT.N ) THEN
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CALL DCOPY( N-K, A( K+1, K ), 1, WORK, 1 )
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CALL DSYMV( UPLO, N-K, -ONE, A( K+1, K+1 ), LDA, WORK, 1,
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$ ZERO, A( K+1, K ), 1 )
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A( K, K ) = A( K, K ) - DDOT( N-K, WORK, 1, A( K+1, K ),
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$ 1 )
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END IF
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KSTEP = 1
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ELSE
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*
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* 2 x 2 diagonal block
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*
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* Invert the diagonal block.
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*
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T = ABS( A( K, K-1 ) )
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AK = A( K-1, K-1 ) / T
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AKP1 = A( K, K ) / T
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AKKP1 = A( K, K-1 ) / T
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D = T*( AK*AKP1-ONE )
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A( K-1, K-1 ) = AKP1 / D
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A( K, K ) = AK / D
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A( K, K-1 ) = -AKKP1 / D
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*
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* Compute columns K-1 and K of the inverse.
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*
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IF( K.LT.N ) THEN
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CALL DCOPY( N-K, A( K+1, K ), 1, WORK, 1 )
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CALL DSYMV( UPLO, N-K, -ONE, A( K+1, K+1 ), LDA, WORK, 1,
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$ ZERO, A( K+1, K ), 1 )
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A( K, K ) = A( K, K ) - DDOT( N-K, WORK, 1, A( K+1, K ),
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$ 1 )
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A( K, K-1 ) = A( K, K-1 ) -
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$ DDOT( N-K, A( K+1, K ), 1, A( K+1, K-1 ),
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$ 1 )
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CALL DCOPY( N-K, A( K+1, K-1 ), 1, WORK, 1 )
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CALL DSYMV( UPLO, N-K, -ONE, A( K+1, K+1 ), LDA, WORK, 1,
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$ ZERO, A( K+1, K-1 ), 1 )
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A( K-1, K-1 ) = A( K-1, K-1 ) -
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$ DDOT( N-K, WORK, 1, A( K+1, K-1 ), 1 )
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END IF
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KSTEP = 2
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END IF
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*
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KP = ABS( IPIV( K ) )
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IF( KP.NE.K ) THEN
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*
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* Interchange rows and columns K and KP in the trailing
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* submatrix A(k-1:n,k-1:n)
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*
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IF( KP.LT.N )
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$ CALL DSWAP( N-KP, A( KP+1, K ), 1, A( KP+1, KP ), 1 )
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CALL DSWAP( KP-K-1, A( K+1, K ), 1, A( KP, K+1 ), LDA )
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TEMP = A( K, K )
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A( K, K ) = A( KP, KP )
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A( KP, KP ) = TEMP
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IF( KSTEP.EQ.2 ) THEN
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TEMP = A( K, K-1 )
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A( K, K-1 ) = A( KP, K-1 )
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A( KP, K-1 ) = TEMP
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END IF
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END IF
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*
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K = K - KSTEP
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GO TO 50
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60 CONTINUE
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END IF
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*
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RETURN
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*
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* End of DSYTRI
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*
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END
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