      SUBROUTINE DORGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )
*
*  -- LAPACK 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 ..
      INTEGER            IHI, ILO, INFO, LDA, LWORK, N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   A( LDA, * ), TAU( * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  DORGHR generates a real orthogonal matrix Q which is defined as the
*  product of IHI-ILO elementary reflectors of order N, as returned by
*  DGEHRD:
*
*  Q = H(ilo) H(ilo+1) . . . H(ihi-1).
*
*  Arguments
*  =========
*
*  N       (input) INTEGER
*          The order of the matrix Q. N >= 0.
*
*  ILO     (input) INTEGER
*  IHI     (input) INTEGER
*          ILO and IHI must have the same values as in the previous call
*          of DGEHRD. Q is equal to the unit matrix except in the
*          submatrix Q(ilo+1:ihi,ilo+1:ihi).
*          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
*
*  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
*          On entry, the vectors which define the elementary reflectors,
*          as returned by DGEHRD.
*          On exit, the N-by-N orthogonal matrix Q.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A. LDA >= max(1,N).
*
*  TAU     (input) DOUBLE PRECISION array, dimension (N-1)
*          TAU(i) must contain the scalar factor of the elementary
*          reflector H(i), as returned by DGEHRD.
*
*  WORK    (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK))
*          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*
*  LWORK   (input) INTEGER
*          The dimension of the array WORK. LWORK >= IHI-ILO.
*          For optimum performance LWORK >= (IHI-ILO)*NB, where NB is
*          the optimal blocksize.
*
*          If LWORK = -1, then a workspace query is assumed; the routine
*          only calculates the optimal size of the WORK array, returns
*          this value as the first entry of the WORK array, and no error
*          message related to LWORK is issued by XERBLA.
*
*  INFO    (output) INTEGER
*          = 0:  successful exit
*          < 0:  if INFO = -i, the i-th argument had an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ZERO, ONE
      PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            LQUERY
      INTEGER            I, IINFO, J, LWKOPT, NB, NH
*     ..
*     .. External Subroutines ..
      EXTERNAL           DORGQR, XERBLA
*     ..
*     .. External Functions ..
      INTEGER            ILAENV
      EXTERNAL           ILAENV
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          MAX, MIN
*     ..
*     .. Executable Statements ..
*
*     Test the input arguments
*
      INFO = 0
      NH = IHI - ILO
      LQUERY = ( LWORK.EQ.-1 )
      IF( N.LT.0 ) THEN
         INFO = -1
      ELSE IF( ILO.LT.1 .OR. ILO.GT.MAX( 1, N ) ) THEN
         INFO = -2
      ELSE IF( IHI.LT.MIN( ILO, N ) .OR. IHI.GT.N ) THEN
         INFO = -3
      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
         INFO = -5
      ELSE IF( LWORK.LT.MAX( 1, NH ) .AND. .NOT.LQUERY ) THEN
         INFO = -8
      END IF
*
      IF( INFO.EQ.0 ) THEN
         NB = ILAENV( 1, 'DORGQR', ' ', NH, NH, NH, -1 )
         LWKOPT = MAX( 1, NH )*NB
         WORK( 1 ) = LWKOPT
      END IF
*
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'DORGHR', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
*
*     Quick return if possible
*
      IF( N.EQ.0 ) THEN
         WORK( 1 ) = 1
         RETURN
      END IF
*
*     Shift the vectors which define the elementary reflectors one
*     column to the right, and set the first ilo and the last n-ihi
*     rows and columns to those of the unit matrix
*
      DO 40 J = IHI, ILO + 1, -1
         DO 10 I = 1, J - 1
            A( I, J ) = ZERO
   10    CONTINUE
         DO 20 I = J + 1, IHI
            A( I, J ) = A( I, J-1 )
   20    CONTINUE
         DO 30 I = IHI + 1, N
            A( I, J ) = ZERO
   30    CONTINUE
   40 CONTINUE
      DO 60 J = 1, ILO
         DO 50 I = 1, N
            A( I, J ) = ZERO
   50    CONTINUE
         A( J, J ) = ONE
   60 CONTINUE
      DO 80 J = IHI + 1, N
         DO 70 I = 1, N
            A( I, J ) = ZERO
   70    CONTINUE
         A( J, J ) = ONE
   80 CONTINUE
*
      IF( NH.GT.0 ) THEN
*
*        Generate Q(ilo+1:ihi,ilo+1:ihi)
*
         CALL DORGQR( NH, NH, NH, A( ILO+1, ILO+1 ), LDA, TAU( ILO ),
     $                WORK, LWORK, IINFO )
      END IF
      WORK( 1 ) = LWKOPT
      RETURN
*
*     End of DORGHR
*
      END
