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- SUBROUTINE DORGLQ( M, N, K, A, LDA, TAU, WORK, LWORK, INFO )
-*
-* -- LAPACK routine (version 3.1) --
-* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
-* November 2006
-*
-* .. Scalar Arguments ..
- INTEGER INFO, K, LDA, LWORK, M, N
-* ..
-* .. Array Arguments ..
- DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
-* ..
-*
-* Purpose
-* =======
-*
-* DORGLQ generates an M-by-N real matrix Q with orthonormal rows,
-* which is defined as the first M rows of a product of K elementary
-* reflectors of order N
-*
-* Q = H(k) . . . H(2) H(1)
-*
-* as returned by DGELQF.
-*
-* Arguments
-* =========
-*
-* M (input) INTEGER
-* The number of rows of the matrix Q. M >= 0.
-*
-* N (input) INTEGER
-* The number of columns of the matrix Q. N >= M.
-*
-* K (input) INTEGER
-* The number of elementary reflectors whose product defines the
-* matrix Q. M >= K >= 0.
-*
-* A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
-* On entry, the i-th row must contain the vector which defines
-* the elementary reflector H(i), for i = 1,2,...,k, as returned
-* by DGELQF in the first k rows of its array argument A.
-* On exit, the M-by-N matrix Q.
-*
-* LDA (input) INTEGER
-* The first dimension of the array A. LDA >= max(1,M).
-*
-* TAU (input) DOUBLE PRECISION array, dimension (K)
-* TAU(i) must contain the scalar factor of the elementary
-* reflector H(i), as returned by DGELQF.
-*
-* 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 >= max(1,M).
-* For optimum performance LWORK >= M*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 has an illegal value
-*
-* =====================================================================
-*
-* .. Parameters ..
- DOUBLE PRECISION ZERO
- PARAMETER ( ZERO = 0.0D+0 )
-* ..
-* .. Local Scalars ..
- LOGICAL LQUERY
- INTEGER I, IB, IINFO, IWS, J, KI, KK, L, LDWORK,
- $ LWKOPT, NB, NBMIN, NX
-* ..
-* .. External Subroutines ..
- EXTERNAL DLARFB, DLARFT, DORGL2, XERBLA
-* ..
-* .. Intrinsic Functions ..
- INTRINSIC MAX, MIN
-* ..
-* .. External Functions ..
- INTEGER ILAENV
- EXTERNAL ILAENV
-* ..
-* .. Executable Statements ..
-*
-* Test the input arguments
-*
- INFO = 0
- NB = ILAENV( 1, 'DORGLQ', ' ', M, N, K, -1 )
- LWKOPT = MAX( 1, M )*NB
- WORK( 1 ) = LWKOPT
- LQUERY = ( LWORK.EQ.-1 )
- IF( M.LT.0 ) THEN
- INFO = -1
- ELSE IF( N.LT.M ) THEN
- INFO = -2
- ELSE IF( K.LT.0 .OR. K.GT.M ) THEN
- INFO = -3
- ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
- INFO = -5
- ELSE IF( LWORK.LT.MAX( 1, M ) .AND. .NOT.LQUERY ) THEN
- INFO = -8
- END IF
- IF( INFO.NE.0 ) THEN
- CALL XERBLA( 'DORGLQ', -INFO )
- RETURN
- ELSE IF( LQUERY ) THEN
- RETURN
- END IF
-*
-* Quick return if possible
-*
- IF( M.LE.0 ) THEN
- WORK( 1 ) = 1
- RETURN
- END IF
-*
- NBMIN = 2
- NX = 0
- IWS = M
- IF( NB.GT.1 .AND. NB.LT.K ) THEN
-*
-* Determine when to cross over from blocked to unblocked code.
-*
- NX = MAX( 0, ILAENV( 3, 'DORGLQ', ' ', M, N, K, -1 ) )
- IF( NX.LT.K ) THEN
-*
-* Determine if workspace is large enough for blocked code.
-*
- LDWORK = M
- IWS = LDWORK*NB
- IF( LWORK.LT.IWS ) THEN
-*
-* Not enough workspace to use optimal NB: reduce NB and
-* determine the minimum value of NB.
-*
- NB = LWORK / LDWORK
- NBMIN = MAX( 2, ILAENV( 2, 'DORGLQ', ' ', M, N, K, -1 ) )
- END IF
- END IF
- END IF
-*
- IF( NB.GE.NBMIN .AND. NB.LT.K .AND. NX.LT.K ) THEN
-*
-* Use blocked code after the last block.
-* The first kk rows are handled by the block method.
-*
- KI = ( ( K-NX-1 ) / NB )*NB
- KK = MIN( K, KI+NB )
-*
-* Set A(kk+1:m,1:kk) to zero.
-*
- DO 20 J = 1, KK
- DO 10 I = KK + 1, M
- A( I, J ) = ZERO
- 10 CONTINUE
- 20 CONTINUE
- ELSE
- KK = 0
- END IF
-*
-* Use unblocked code for the last or only block.
-*
- IF( KK.LT.M )
- $ CALL DORGL2( M-KK, N-KK, K-KK, A( KK+1, KK+1 ), LDA,
- $ TAU( KK+1 ), WORK, IINFO )
-*
- IF( KK.GT.0 ) THEN
-*
-* Use blocked code
-*
- DO 50 I = KI + 1, 1, -NB
- IB = MIN( NB, K-I+1 )
- IF( I+IB.LE.M ) THEN
-*
-* Form the triangular factor of the block reflector
-* H = H(i) H(i+1) . . . H(i+ib-1)
-*
- CALL DLARFT( 'Forward', 'Rowwise', N-I+1, IB, A( I, I ),
- $ LDA, TAU( I ), WORK, LDWORK )
-*
-* Apply H' to A(i+ib:m,i:n) from the right
-*
- CALL DLARFB( 'Right', 'Transpose', 'Forward', 'Rowwise',
- $ M-I-IB+1, N-I+1, IB, A( I, I ), LDA, WORK,
- $ LDWORK, A( I+IB, I ), LDA, WORK( IB+1 ),
- $ LDWORK )
- END IF
-*
-* Apply H' to columns i:n of current block
-*
- CALL DORGL2( IB, N-I+1, IB, A( I, I ), LDA, TAU( I ), WORK,
- $ IINFO )
-*
-* Set columns 1:i-1 of current block to zero
-*
- DO 40 J = 1, I - 1
- DO 30 L = I, I + IB - 1
- A( L, J ) = ZERO
- 30 CONTINUE
- 40 CONTINUE
- 50 CONTINUE
- END IF
-*
- WORK( 1 ) = IWS
- RETURN
-*
-* End of DORGLQ
-*
- END