223 lines
6.2 KiB
FortranFixed
223 lines
6.2 KiB
FortranFixed
SUBROUTINE SORGQL( M, N, K, A, LDA, TAU, WORK, LWORK, INFO )
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*
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* -- LAPACK 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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INTEGER INFO, K, LDA, LWORK, M, N
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* ..
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* .. Array Arguments ..
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REAL A( LDA, * ), TAU( * ), WORK( * )
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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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* SORGQL generates an M-by-N real matrix Q with orthonormal columns,
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* which is defined as the last N columns of a product of K elementary
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* reflectors of order M
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*
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* Q = H(k) . . . H(2) H(1)
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*
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* as returned by SGEQLF.
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*
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* Arguments
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* =========
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*
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* M (input) INTEGER
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* The number of rows of the matrix Q. M >= 0.
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*
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* N (input) INTEGER
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* The number of columns of the matrix Q. M >= N >= 0.
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*
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* K (input) INTEGER
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* The number of elementary reflectors whose product defines the
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* matrix Q. N >= K >= 0.
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*
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* A (input/output) REAL array, dimension (LDA,N)
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* On entry, the (n-k+i)-th column must contain the vector which
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* defines the elementary reflector H(i), for i = 1,2,...,k, as
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* returned by SGEQLF in the last k columns of its array
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* argument A.
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* On exit, the M-by-N matrix Q.
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*
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* LDA (input) INTEGER
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* The first dimension of the array A. LDA >= max(1,M).
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*
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* TAU (input) REAL array, dimension (K)
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* TAU(i) must contain the scalar factor of the elementary
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* reflector H(i), as returned by SGEQLF.
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*
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* WORK (workspace/output) REAL array, dimension (MAX(1,LWORK))
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* On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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*
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* LWORK (input) INTEGER
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* The dimension of the array WORK. LWORK >= max(1,N).
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* For optimum performance LWORK >= N*NB, where NB is the
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* optimal blocksize.
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*
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* If LWORK = -1, then a workspace query is assumed; the routine
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* only calculates the optimal size of the WORK array, returns
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* this value as the first entry of the WORK array, and no error
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* message related to LWORK is issued by XERBLA.
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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 = -i, the i-th argument has an illegal value
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ZERO
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PARAMETER ( ZERO = 0.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL LQUERY
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INTEGER I, IB, IINFO, IWS, J, KK, L, LDWORK, LWKOPT,
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$ NB, NBMIN, NX
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* ..
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* .. External Subroutines ..
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EXTERNAL SLARFB, SLARFT, SORG2L, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX, MIN
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* ..
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* .. External Functions ..
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INTEGER ILAENV
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EXTERNAL ILAENV
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* ..
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* .. Executable Statements ..
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*
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* Test the input arguments
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*
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INFO = 0
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LQUERY = ( LWORK.EQ.-1 )
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IF( M.LT.0 ) THEN
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INFO = -1
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ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
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INFO = -2
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ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
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INFO = -3
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ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
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INFO = -5
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END IF
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*
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IF( INFO.EQ.0 ) THEN
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IF( N.EQ.0 ) THEN
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LWKOPT = 1
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ELSE
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NB = ILAENV( 1, 'SORGQL', ' ', M, N, K, -1 )
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LWKOPT = N*NB
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END IF
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WORK( 1 ) = LWKOPT
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*
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IF( LWORK.LT.MAX( 1, N ) .AND. .NOT.LQUERY ) THEN
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INFO = -8
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END IF
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END IF
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*
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SORGQL', -INFO )
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RETURN
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ELSE IF( LQUERY ) THEN
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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.LE.0 ) THEN
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RETURN
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END IF
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*
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NBMIN = 2
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NX = 0
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IWS = N
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IF( NB.GT.1 .AND. NB.LT.K ) THEN
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*
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* Determine when to cross over from blocked to unblocked code.
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*
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NX = MAX( 0, ILAENV( 3, 'SORGQL', ' ', M, N, K, -1 ) )
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IF( NX.LT.K ) THEN
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*
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* Determine if workspace is large enough for blocked code.
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*
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LDWORK = N
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IWS = LDWORK*NB
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IF( LWORK.LT.IWS ) THEN
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*
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* Not enough workspace to use optimal NB: reduce NB and
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* determine the minimum value of NB.
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*
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NB = LWORK / LDWORK
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NBMIN = MAX( 2, ILAENV( 2, 'SORGQL', ' ', M, N, K, -1 ) )
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END IF
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END IF
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END IF
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*
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IF( NB.GE.NBMIN .AND. NB.LT.K .AND. NX.LT.K ) THEN
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*
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* Use blocked code after the first block.
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* The last kk columns are handled by the block method.
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*
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KK = MIN( K, ( ( K-NX+NB-1 ) / NB )*NB )
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*
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* Set A(m-kk+1:m,1:n-kk) to zero.
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*
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DO 20 J = 1, N - KK
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DO 10 I = M - KK + 1, M
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A( I, J ) = ZERO
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10 CONTINUE
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20 CONTINUE
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ELSE
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KK = 0
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END IF
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*
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* Use unblocked code for the first or only block.
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*
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CALL SORG2L( M-KK, N-KK, K-KK, A, LDA, TAU, WORK, IINFO )
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*
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IF( KK.GT.0 ) THEN
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*
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* Use blocked code
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*
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DO 50 I = K - KK + 1, K, NB
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IB = MIN( NB, K-I+1 )
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IF( N-K+I.GT.1 ) THEN
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*
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* Form the triangular factor of the block reflector
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* H = H(i+ib-1) . . . H(i+1) H(i)
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*
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CALL SLARFT( 'Backward', 'Columnwise', M-K+I+IB-1, IB,
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$ A( 1, N-K+I ), LDA, TAU( I ), WORK, LDWORK )
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*
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* Apply H to A(1:m-k+i+ib-1,1:n-k+i-1) from the left
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*
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CALL SLARFB( 'Left', 'No transpose', 'Backward',
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$ 'Columnwise', M-K+I+IB-1, N-K+I-1, IB,
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$ A( 1, N-K+I ), LDA, WORK, LDWORK, A, LDA,
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$ WORK( IB+1 ), LDWORK )
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END IF
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*
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* Apply H to rows 1:m-k+i+ib-1 of current block
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*
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CALL SORG2L( M-K+I+IB-1, IB, IB, A( 1, N-K+I ), LDA,
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$ TAU( I ), WORK, IINFO )
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*
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* Set rows m-k+i+ib:m of current block to zero
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*
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DO 40 J = N - K + I, N - K + I + IB - 1
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DO 30 L = M - K + I + IB, M
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A( L, J ) = ZERO
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30 CONTINUE
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40 CONTINUE
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50 CONTINUE
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END IF
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*
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WORK( 1 ) = IWS
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RETURN
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*
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* End of SORGQL
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*
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END
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