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*> \brief \b DASUM
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* DOUBLE PRECISION FUNCTION DASUM(N,DX,INCX)
*
* .. Scalar Arguments ..
* INTEGER INCX,N
* ..
* .. Array Arguments ..
* DOUBLE PRECISION DX(*)
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> DASUM takes the sum of the absolute values.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in] DX
*> \verbatim
*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*> INCX is INTEGER
*> storage spacing between elements of DX
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup asum
*
*> \par Further Details:
* =====================
*>
*> \verbatim
*>
*> jack dongarra, linpack, 3/11/78.
*> modified 3/93 to return if incx .le. 0.
*> modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
* =====================================================================
DOUBLE PRECISION FUNCTION DASUM(N,DX,INCX)
*
* -- Reference BLAS level1 routine --
* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
* .. Scalar Arguments ..
INTEGER INCX,N
* ..
* .. Array Arguments ..
DOUBLE PRECISION DX(*)
* ..
*
* =====================================================================
*
* .. Local Scalars ..
DOUBLE PRECISION DTEMP
INTEGER I,M,MP1,NINCX
* ..
* .. Intrinsic Functions ..
INTRINSIC DABS,MOD
* ..
DASUM = 0.0d0
DTEMP = 0.0d0
IF (N.LE.0 .OR. INCX.LE.0) RETURN
IF (INCX.EQ.1) THEN
* code for increment equal to 1
*
*
* clean-up loop
*
M = MOD(N,6)
IF (M.NE.0) THEN
DO I = 1,M
DTEMP = DTEMP + DABS(DX(I))
END DO
IF (N.LT.6) THEN
DASUM = DTEMP
RETURN
END IF
END IF
MP1 = M + 1
DO I = MP1,N,6
DTEMP = DTEMP + DABS(DX(I)) + DABS(DX(I+1)) +
$ DABS(DX(I+2)) + DABS(DX(I+3)) +
$ DABS(DX(I+4)) + DABS(DX(I+5))
END DO
ELSE
*
* code for increment not equal to 1
*
NINCX = N*INCX
DO I = 1,NINCX,INCX
DTEMP = DTEMP + DABS(DX(I))
END DO
END IF
DASUM = DTEMP
RETURN
*
* End of DASUM
*
END
|
