*> \brief \b DAXPY * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY) * * .. Scalar Arguments .. * DOUBLE PRECISION DA * INTEGER INCX,INCY,N * .. * .. Array Arguments .. * DOUBLE PRECISION DX(*),DY(*) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> DAXPY constant times a vector plus a vector. *> uses unrolled loops for increments equal to one. *> \endverbatim * * Arguments: * ========== * *> \param[in] N *> \verbatim *> N is INTEGER *> number of elements in input vector(s) *> \endverbatim *> *> \param[in] DA *> \verbatim *> DA is DOUBLE PRECISION *> On entry, DA specifies the scalar alpha. *> \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 *> *> \param[in,out] DY *> \verbatim *> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) ) *> \endverbatim *> *> \param[in] INCY *> \verbatim *> INCY is INTEGER *> storage spacing between elements of DY *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup double_blas_level1 * *> \par Further Details: * ===================== *> *> \verbatim *> *> jack dongarra, linpack, 3/11/78. *> modified 12/3/93, array(1) declarations changed to array(*) *> \endverbatim *> * ===================================================================== SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY) * * -- 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 .. DOUBLE PRECISION DA INTEGER INCX,INCY,N * .. * .. Array Arguments .. DOUBLE PRECISION DX(*),DY(*) * .. * * ===================================================================== * * .. Local Scalars .. INTEGER I,IX,IY,M,MP1 * .. * .. Intrinsic Functions .. INTRINSIC MOD * .. IF (N.LE.0) RETURN IF (DA.EQ.0.0d0) RETURN IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN * * code for both increments equal to 1 * * * clean-up loop * M = MOD(N,4) IF (M.NE.0) THEN DO I = 1,M DY(I) = DY(I) + DA*DX(I) END DO END IF IF (N.LT.4) RETURN MP1 = M + 1 DO I = MP1,N,4 DY(I) = DY(I) + DA*DX(I) DY(I+1) = DY(I+1) + DA*DX(I+1) DY(I+2) = DY(I+2) + DA*DX(I+2) DY(I+3) = DY(I+3) + DA*DX(I+3) END DO ELSE * * code for unequal increments or equal increments * not equal to 1 * IX = 1 IY = 1 IF (INCX.LT.0) IX = (-N+1)*INCX + 1 IF (INCY.LT.0) IY = (-N+1)*INCY + 1 DO I = 1,N DY(IY) = DY(IY) + DA*DX(IX) IX = IX + INCX IY = IY + INCY END DO END IF RETURN * * End of DAXPY * END