196 lines
5.3 KiB
Fortran
196 lines
5.3 KiB
Fortran
*> \brief \b SLAUU2 computes the product UUH or LHL, where U and L are upper or lower triangular matrices (unblocked algorithm).
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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 SLAUU2 + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slauu2.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/slauu2.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/slauu2.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 SLAUU2( 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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*
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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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*> SLAUU2 computes the product U * U**T or L**T * L, where the triangular
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*> factor U or L is stored in the upper or lower triangular part of
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*> the array A.
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*>
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*> If UPLO = 'U' or 'u' then the upper triangle of the result is stored,
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*> overwriting the factor U in A.
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*> If UPLO = 'L' or 'l' then the lower triangle of the result is stored,
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*> overwriting the factor L in A.
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*>
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*> This is the unblocked form of the algorithm, calling Level 2 BLAS.
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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 triangular factor stored in the array A
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*> is upper or lower triangular:
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*> = 'U': Upper triangular
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*> = 'L': Lower triangular
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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 triangular factor U or L. 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 REAL array, dimension (LDA,N)
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*> On entry, the triangular factor U or L.
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*> On exit, if UPLO = 'U', the upper triangle of A is
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*> overwritten with the upper triangle of the product U * U**T;
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*> if UPLO = 'L', the lower triangle of A is overwritten with
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*> the lower triangle of the product L**T * L.
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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[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 = -k, the k-th argument had an illegal value
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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 realOTHERauxiliary
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*
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* =====================================================================
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SUBROUTINE SLAUU2( UPLO, N, A, LDA, INFO )
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*
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* -- LAPACK auxiliary 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 I
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REAL AII
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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REAL SDOT
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EXTERNAL LSAME, SDOT
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* ..
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* .. External Subroutines ..
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EXTERNAL SGEMV, SSCAL, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC 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( 'SLAUU2', -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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IF( UPPER ) THEN
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*
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* Compute the product U * U**T.
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*
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DO 10 I = 1, N
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AII = A( I, I )
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IF( I.LT.N ) THEN
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A( I, I ) = SDOT( N-I+1, A( I, I ), LDA, A( I, I ), LDA )
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CALL SGEMV( 'No transpose', I-1, N-I, ONE, A( 1, I+1 ),
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$ LDA, A( I, I+1 ), LDA, AII, A( 1, I ), 1 )
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ELSE
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CALL SSCAL( I, AII, A( 1, I ), 1 )
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END IF
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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 product L**T * L.
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*
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DO 20 I = 1, N
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AII = A( I, I )
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IF( I.LT.N ) THEN
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A( I, I ) = SDOT( N-I+1, A( I, I ), 1, A( I, I ), 1 )
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CALL SGEMV( 'Transpose', N-I, I-1, ONE, A( I+1, 1 ), LDA,
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$ A( I+1, I ), 1, AII, A( I, 1 ), LDA )
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ELSE
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CALL SSCAL( I, AII, A( I, 1 ), LDA )
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END IF
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20 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 SLAUU2
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*
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END
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