SUBROUTINE DLAUU2( UPLO, N, A, LDA, INFO ) * * -- LAPACK auxiliary routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. CHARACTER UPLO INTEGER INFO, LDA, N * .. * .. Array Arguments .. DOUBLE PRECISION A( LDA, * ) * .. * * Purpose * ======= * * DLAUU2 computes the product U * U' or L' * L, where the triangular * factor U or L is stored in the upper or lower triangular part of * the array A. * * If UPLO = 'U' or 'u' then the upper triangle of the result is stored, * overwriting the factor U in A. * If UPLO = 'L' or 'l' then the lower triangle of the result is stored, * overwriting the factor L in A. * * This is the unblocked form of the algorithm, calling Level 2 BLAS. * * Arguments * ========= * * UPLO (input) CHARACTER*1 * Specifies whether the triangular factor stored in the array A * is upper or lower triangular: * = 'U': Upper triangular * = 'L': Lower triangular * * N (input) INTEGER * The order of the triangular factor U or L. N >= 0. * * A (input/output) DOUBLE PRECISION array, dimension (LDA,N) * On entry, the triangular factor U or L. * On exit, if UPLO = 'U', the upper triangle of A is * overwritten with the upper triangle of the product U * U'; * if UPLO = 'L', the lower triangle of A is overwritten with * the lower triangle of the product L' * L. * * LDA (input) INTEGER * The leading dimension of the array A. LDA >= max(1,N). * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -k, the k-th argument had an illegal value * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ONE PARAMETER ( ONE = 1.0D+0 ) * .. * .. Local Scalars .. LOGICAL UPPER INTEGER I DOUBLE PRECISION AII * .. * .. External Functions .. LOGICAL LSAME DOUBLE PRECISION DDOT EXTERNAL LSAME, DDOT * .. * .. External Subroutines .. EXTERNAL DGEMV, DSCAL, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 UPPER = LSAME( UPLO, 'U' ) IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -4 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'DLAUU2', -INFO ) RETURN END IF * * Quick return if possible * IF( N.EQ.0 ) \$ RETURN * IF( UPPER ) THEN * * Compute the product U * U'. * DO 10 I = 1, N AII = A( I, I ) IF( I.LT.N ) THEN A( I, I ) = DDOT( N-I+1, A( I, I ), LDA, A( I, I ), LDA ) CALL DGEMV( 'No transpose', I-1, N-I, ONE, A( 1, I+1 ), \$ LDA, A( I, I+1 ), LDA, AII, A( 1, I ), 1 ) ELSE CALL DSCAL( I, AII, A( 1, I ), 1 ) END IF 10 CONTINUE * ELSE * * Compute the product L' * L. * DO 20 I = 1, N AII = A( I, I ) IF( I.LT.N ) THEN A( I, I ) = DDOT( N-I+1, A( I, I ), 1, A( I, I ), 1 ) CALL DGEMV( 'Transpose', N-I, I-1, ONE, A( I+1, 1 ), LDA, \$ A( I+1, I ), 1, AII, A( I, 1 ), LDA ) ELSE CALL DSCAL( I, AII, A( I, 1 ), LDA ) END IF 20 CONTINUE END IF * RETURN * * End of DLAUU2 * END