116 lines
3 KiB
Fortran
116 lines
3 KiB
Fortran
SUBROUTINE DLARF( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
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*
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* -- LAPACK auxiliary routine (version 2.0) --
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* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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* Courant Institute, Argonne National Lab, and Rice University
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* February 29, 1992
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*
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* .. Scalar Arguments ..
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CHARACTER SIDE
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INTEGER INCV, LDC, M, N
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DOUBLE PRECISION TAU
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION C( LDC, * ), V( * ), 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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* DLARF applies a real elementary reflector H to a real m by n matrix
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* C, from either the left or the right. H is represented in the form
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*
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* H = I - tau * v * v'
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*
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* where tau is a real scalar and v is a real vector.
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*
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* If tau = 0, then H is taken to be the unit matrix.
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*
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* Arguments
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* =========
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*
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* SIDE (input) CHARACTER*1
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* = 'L': form H * C
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* = 'R': form C * H
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*
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* M (input) INTEGER
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* The number of rows of the matrix C.
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*
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* N (input) INTEGER
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* The number of columns of the matrix C.
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*
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* V (input) DOUBLE PRECISION array, dimension
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* (1 + (M-1)*abs(INCV)) if SIDE = 'L'
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* or (1 + (N-1)*abs(INCV)) if SIDE = 'R'
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* The vector v in the representation of H. V is not used if
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* TAU = 0.
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*
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* INCV (input) INTEGER
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* The increment between elements of v. INCV <> 0.
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*
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* TAU (input) DOUBLE PRECISION
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* The value tau in the representation of H.
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*
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* C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
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* On entry, the m by n matrix C.
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* On exit, C is overwritten by the matrix H * C if SIDE = 'L',
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* or C * H if SIDE = 'R'.
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*
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* LDC (input) INTEGER
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* The leading dimension of the array C. LDC >= max(1,M).
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*
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* WORK (workspace) DOUBLE PRECISION array, dimension
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* (N) if SIDE = 'L'
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* or (M) if SIDE = 'R'
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*
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* =====================================================================
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*
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* .. Parameters ..
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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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* ..
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* .. External Subroutines ..
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EXTERNAL DGEMV, DGER
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* ..
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* .. Executable Statements ..
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*
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IF( LSAME( SIDE, 'L' ) ) THEN
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*
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* Form H * C
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*
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IF( TAU.NE.ZERO ) THEN
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*
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* w := C' * v
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*
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CALL DGEMV( 'Transpose', M, N, ONE, C, LDC, V, INCV, ZERO,
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$ WORK, 1 )
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*
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* C := C - v * w'
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*
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CALL DGER( M, N, -TAU, V, INCV, WORK, 1, C, LDC )
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END IF
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ELSE
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*
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* Form C * H
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*
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IF( TAU.NE.ZERO ) THEN
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*
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* w := C * v
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*
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CALL DGEMV( 'No transpose', M, N, ONE, C, LDC, V, INCV,
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$ ZERO, WORK, 1 )
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*
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* C := C - w * v'
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*
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CALL DGER( M, N, -TAU, WORK, 1, V, INCV, C, LDC )
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END IF
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END IF
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RETURN
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*
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* End of DLARF
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*
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END
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