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SUBROUTINE DGEQRF( M, N, A, LDA, TAU, WORK, LWORK, INFO )
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* -- LAPACK routine (version 3.2) --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* -- Modified by R. Clint Whaley for ATLAS Fortran77 LAPACK interface, 2009
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* .. Scalar Arguments ..
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INTEGER INFO, LDA, LWORK, M, N
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* .. Array Arguments ..
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DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
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* DGEQRF computes a QR factorization of a real M-by-N matrix A:
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* The number of rows of the matrix A. M >= 0.
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* The number of columns of the matrix A. N >= 0.
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* A (input/output) COMPLEX*16 array, dimension (LDA,N)
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* On entry, the M-by-N matrix A.
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* On exit, the elements on and above the diagonal of the array
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* contain the min(M,N)-by-N upper trapezoidal matrix R (R is
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* upper triangular if m >= n); the elements below the diagonal,
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* with the array TAU, represent the orthogonal matrix Q as a
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* product of min(m,n) elementary reflectors (see Further
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* The leading dimension of the array A. LDA >= max(1,M).
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* TAU (output) DOUBLE PRECISION array, dimension (min(M,N))
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* The scalar factors of the elementary reflectors (see Further
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* WORK (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK))
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* On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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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
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* the optimal blocksize.
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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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* INFO (output) INTEGER
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* = 0: successful exit
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* < 0: if INFO = -i, the i-th argument had an illegal value
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* The matrix Q is represented as a product of elementary reflectors
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* Q = H(1) H(2) . . . H(k), where k = min(m,n).
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* Each H(i) has the form
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* H(i) = I - tau * v * v**T
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* where tau is a real scalar, and v is a real vector with
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* v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),
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* =====================================================================
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INTEGER I, IB, IINFO, IWS, K, LDWORK, LWKOPT, NB,
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* .. External Subroutines ..
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EXTERNAL XERBLA, ZGEQR2, ZLARFB, ZLARFT
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* .. Intrinsic Functions ..
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* .. External Functions ..
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* .. Executable Statements ..
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* Test the input arguments
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ELSE IF( N.LT.0 ) THEN
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ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
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CALL XERBLA( 'Dgeqrf', -INFO )
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* Quick return if possible
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CALL ATL_F77WRAP_DGEQRF(M, N, A, LDA, TAU, WORK, LWORK, INFO)
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interfaces/lapack/F77/src/dgeqrf.f
