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237 lines
6.2 KiB
237 lines
6.2 KiB
2 years ago
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C> \brief \b SPOTRF VARIANT: top-looking block version of the algorithm, calling Level 3 BLAS.
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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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* Definition:
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* ===========
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*
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* SUBROUTINE SPOTRF ( UPLO, N, A, LDA, 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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* REAL A( LDA, * )
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* ..
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*
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* Purpose
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* =======
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*
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C>\details \b Purpose:
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C>\verbatim
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C>
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C> SPOTRF computes the Cholesky factorization of a real symmetric
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C> positive definite matrix A.
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C>
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C> The factorization has the form
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C> A = U**T * U, if UPLO = 'U', or
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C> A = L * L**T, if UPLO = 'L',
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C> where U is an upper triangular matrix and L is lower triangular.
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C>
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C> This is the top-looking block version of the algorithm, calling Level 3 BLAS.
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C>
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C>\endverbatim
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*
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* Arguments:
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* ==========
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*
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C> \param[in] UPLO
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C> \verbatim
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C> UPLO is CHARACTER*1
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C> = 'U': Upper triangle of A is stored;
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C> = 'L': Lower triangle of A is stored.
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C> \endverbatim
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C>
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C> \param[in] N
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C> \verbatim
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C> N is INTEGER
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C> The order of the matrix A. N >= 0.
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C> \endverbatim
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C>
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C> \param[in,out] A
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C> \verbatim
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C> A is REAL array, dimension (LDA,N)
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C> On entry, the symmetric matrix A. If UPLO = 'U', the leading
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C> N-by-N upper triangular part of A contains the upper
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C> triangular part of the matrix A, and the strictly lower
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C> triangular part of A is not referenced. If UPLO = 'L', the
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C> leading N-by-N lower triangular part of A contains the lower
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C> triangular part of the matrix A, and the strictly upper
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C> triangular part of A is not referenced.
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C> \endverbatim
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C> \verbatim
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C> On exit, if INFO = 0, the factor U or L from the Cholesky
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C> factorization A = U**T*U or A = L*L**T.
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C> \endverbatim
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C>
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C> \param[in] LDA
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C> \verbatim
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C> LDA is INTEGER
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C> The leading dimension of the array A. LDA >= max(1,N).
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C> \endverbatim
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C>
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C> \param[out] INFO
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C> \verbatim
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C> INFO is INTEGER
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C> = 0: successful exit
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C> < 0: if INFO = -i, the i-th argument had an illegal value
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C> > 0: if INFO = i, the leading principal minor of order i
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C> is not positive, and the factorization could not be
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C> completed.
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C> \endverbatim
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C>
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*
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* Authors:
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* ========
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*
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C> \author Univ. of Tennessee
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C> \author Univ. of California Berkeley
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C> \author Univ. of Colorado Denver
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C> \author NAG Ltd.
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*
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C> \date December 2016
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*
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C> \ingroup variantsPOcomputational
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*
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* =====================================================================
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SUBROUTINE SPOTRF ( UPLO, N, A, LDA, 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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REAL A( LDA, * )
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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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REAL ONE
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PARAMETER ( ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL UPPER
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INTEGER J, JB, NB
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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INTEGER ILAENV
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EXTERNAL LSAME, ILAENV
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* ..
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* .. External Subroutines ..
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EXTERNAL SGEMM, SPOTF2, SSYRK, STRSM, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX, MIN
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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( 'SPOTRF', -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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* Determine the block size for this environment.
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*
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NB = ILAENV( 1, 'SPOTRF', UPLO, N, -1, -1, -1 )
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IF( NB.LE.1 .OR. NB.GE.N ) THEN
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*
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* Use unblocked code.
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*
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CALL SPOTF2( UPLO, N, A, LDA, INFO )
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ELSE
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*
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* Use blocked code.
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*
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IF( UPPER ) THEN
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*
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* Compute the Cholesky factorization A = U'*U.
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*
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DO 10 J = 1, N, NB
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JB = MIN( NB, N-J+1 )
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*
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* Compute the current block.
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*
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CALL STRSM( 'Left', 'Upper', 'Transpose', 'Non-unit',
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$ J-1, JB, ONE, A( 1, 1 ), LDA,
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$ A( 1, J ), LDA )
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CALL SSYRK( 'Upper', 'Transpose', JB, J-1, -ONE,
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$ A( 1, J ), LDA,
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$ ONE, A( J, J ), LDA )
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*
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* Update and factorize the current diagonal block and test
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* for non-positive-definiteness.
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*
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CALL SPOTF2( 'Upper', JB, A( J, J ), LDA, INFO )
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IF( INFO.NE.0 )
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$ GO TO 30
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10 CONTINUE
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*
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ELSE
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*
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* Compute the Cholesky factorization A = L*L'.
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*
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DO 20 J = 1, N, NB
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JB = MIN( NB, N-J+1 )
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*
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* Compute the current block.
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*
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CALL STRSM( 'Right', 'Lower', 'Transpose', 'Non-unit',
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$ JB, J-1, ONE, A( 1, 1 ), LDA,
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$ A( J, 1 ), LDA )
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CALL SSYRK( 'Lower', 'No Transpose', JB, J-1,
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$ -ONE, A( J, 1 ), LDA,
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$ ONE, A( J, J ), LDA )
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*
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* Update and factorize the current diagonal block and test
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* for non-positive-definiteness.
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*
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CALL SPOTF2( 'Lower', JB, A( J, J ), LDA, INFO )
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IF( INFO.NE.0 )
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$ GO TO 30
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20 CONTINUE
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END IF
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END IF
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GO TO 40
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*
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30 CONTINUE
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INFO = INFO + J - 1
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*
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40 CONTINUE
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RETURN
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*
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* End of SPOTRF
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*
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END
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