135 lines
3.7 KiB
Fortran
135 lines
3.7 KiB
Fortran
SUBROUTINE DLAUU2F( UPLO, N, A, LDA, INFO )
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*
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* -- LAPACK auxiliary routine (version 3.1) --
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* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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* November 2006
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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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DOUBLE PRECISION 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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* DLAUU2 computes the product U * U' or L' * 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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*
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* Arguments
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* =========
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*
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* UPLO (input) 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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*
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* N (input) INTEGER
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* The order of the triangular factor U or L. N >= 0.
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*
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* A (input/output) DOUBLE PRECISION 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';
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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' * L.
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*
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* LDA (input) INTEGER
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* The leading dimension of the array A. LDA >= max(1,N).
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*
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* INFO (output) 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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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ONE
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PARAMETER ( ONE = 1.0D+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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DOUBLE PRECISION AII
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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 DGEMV, DSCAL, 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( 'DLAUU2', -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'.
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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 ) = DDOT( N-I+1, A( I, I ), LDA, A( I, I ), LDA )
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CALL DGEMV( '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 DSCAL( 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' * 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 ) = DDOT( N-I+1, A( I, I ), 1, A( I, I ), 1 )
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CALL DGEMV( '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 DSCAL( 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 DLAUU2
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*
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END
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