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SUBROUTINE DORG2R( M, N, K, A, LDA, TAU, WORK, INFO )
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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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* .. Scalar Arguments ..
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INTEGER INFO, K, LDA, M, N
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* .. Array Arguments ..
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DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
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* DORG2R generates an m by n real matrix Q with orthonormal columns,
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* which is defined as the first n columns of a product of k elementary
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* reflectors of order m
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* Q = H(1) H(2) . . . H(k)
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* as returned by DGEQRF.
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* The number of rows of the matrix Q. M >= 0.
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* The number of columns of the matrix Q. M >= N >= 0.
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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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* A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
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* On entry, the 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 DGEQRF in the first k columns of its array
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* On exit, the m-by-n matrix Q.
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* The first dimension of the array A. LDA >= max(1,M).
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* TAU (input) DOUBLE PRECISION 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 DGEQRF.
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* WORK (workspace) DOUBLE PRECISION array, dimension (N)
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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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DOUBLE PRECISION ONE, ZERO
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PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
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* .. External Subroutines ..
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EXTERNAL DLARF, DSCAL, XERBLA
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* .. Intrinsic Functions ..
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* .. Executable Statements ..
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* Test the input arguments
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ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
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ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
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ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
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CALL XERBLA( 'DORG2R', -INFO )
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* Quick return if possible
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* Initialise columns k+1:n to columns of the unit matrix
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* Apply H(i) to A(i:m,i:n) from the left
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CALL DLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ),
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$ A( I, I+1 ), LDA, WORK )
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$ CALL DSCAL( M-I, -TAU( I ), A( I+1, I ), 1 )
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A( I, I ) = ONE - TAU( I )
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* Set A(1:i-1,i) to zero