forked from lijiext/lammps
149 lines
3.3 KiB
Fortran
149 lines
3.3 KiB
Fortran
*> \brief \b DDOT
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
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*
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* .. Scalar Arguments ..
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* INTEGER INCX,INCY,N
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION DX(*),DY(*)
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DDOT forms the dot product of two vectors.
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*> uses unrolled loops for increments equal to one.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> number of elements in input vector(s)
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*> \endverbatim
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*>
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*> \param[in] DX
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*> \verbatim
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*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> storage spacing between elements of DX
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*> \endverbatim
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*>
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*> \param[in] DY
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*> \verbatim
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*> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
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*> \endverbatim
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*>
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*> \param[in] INCY
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*> \verbatim
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*> INCY is INTEGER
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*> storage spacing between elements of DY
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date December 2016
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*
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*> \ingroup double_blas_level1
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> jack dongarra, linpack, 3/11/78.
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*> modified 12/3/93, array(1) declarations changed to array(*)
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*> \endverbatim
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*>
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* =====================================================================
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DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
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*
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* -- Reference BLAS level1 routine (version 3.7.0) --
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* -- Reference BLAS 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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* December 2016
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*
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* .. Scalar Arguments ..
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INTEGER INCX,INCY,N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION DX(*),DY(*)
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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DOUBLE PRECISION DTEMP
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INTEGER I,IX,IY,M,MP1
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MOD
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* ..
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DDOT = 0.0d0
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DTEMP = 0.0d0
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IF (N.LE.0) RETURN
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IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
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*
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* code for both increments equal to 1
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*
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*
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* clean-up loop
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*
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M = MOD(N,5)
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IF (M.NE.0) THEN
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DO I = 1,M
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DTEMP = DTEMP + DX(I)*DY(I)
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END DO
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IF (N.LT.5) THEN
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DDOT=DTEMP
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RETURN
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END IF
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END IF
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MP1 = M + 1
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DO I = MP1,N,5
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DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
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$ DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
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END DO
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ELSE
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*
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* code for unequal increments or equal increments
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* not equal to 1
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*
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IX = 1
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IY = 1
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IF (INCX.LT.0) IX = (-N+1)*INCX + 1
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IF (INCY.LT.0) IY = (-N+1)*INCY + 1
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DO I = 1,N
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DTEMP = DTEMP + DX(IX)*DY(IY)
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IX = IX + INCX
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IY = IY + INCY
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END DO
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END IF
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DDOT = DTEMP
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RETURN
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END
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