zaxpy.f

Go to the documentation of this file.

*> \brief \b ZAXPY
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       SUBROUTINE ZAXPY(N,ZA,ZX,INCX,ZY,INCY)
*
*       .. Scalar Arguments ..
*       COMPLEX*16 ZA
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       COMPLEX*16 ZX(*),ZY(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    ZAXPY constant times a vector plus a vector.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in] ZA
*> \verbatim
*>          ZA is COMPLEX*16
*>           On entry, ZA specifies the scalar alpha.
*> \endverbatim
*>
*> \param[in] ZX
*> \verbatim
*>          ZX is COMPLEX*16 array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>         storage spacing between elements of ZX
*> \endverbatim
*>
*> \param[in,out] ZY
*> \verbatim
*>          ZY is COMPLEX*16 array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>         storage spacing between elements of ZY
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup axpy
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>     jack dongarra, 3/11/78.
*>     modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
*  =====================================================================
      SUBROUTINE zaxpy(N,ZA,ZX,INCX,ZY,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 ..
      COMPLEX*16 ZA
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      COMPLEX*16 ZX(*),ZY(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER I,IX,IY
*     ..
*     .. External Functions ..
      DOUBLE PRECISION DCABS1
      EXTERNAL dcabs1
*     ..
      IF (n.LE.0) RETURN
      IF (dcabs1(za).EQ.0.0d0) RETURN
      IF (incx.EQ.1 .AND. incy.EQ.1) THEN
*
*        code for both increments equal to 1
*
         DO i = 1,n
            zy(i) = zy(i) + za*zx(i)
         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
            zy(iy) = zy(iy) + za*zx(ix)
            ix = ix + incx
            iy = iy + incy
         END DO
      END IF
*
      RETURN
*
*     End of ZAXPY
*
      END