SUBROUTINE DLAUU2F( UPLO, N, A, LDA, INFO )

*

*  -- LAPACK auxiliary routine (version 3.1) --

*     Univ. of Tennessee, Univ. of California Berkeley 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