dswap()

subroutine dswap	(	integer	n,
		double precision, dimension(*)	dx,
		integer	incx,
		double precision, dimension(*)	dy,
		integer	incy )

DSWAP

Purpose:

!>
!>    DSWAP interchanges two vectors.
!>    uses unrolled loops for increments equal to 1.
!> 

Parameters

[in]	N	!> N is INTEGER !> number of elements in input vector(s) !>
[in,out]	DX	!> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) ) !>
[in]	INCX	!> INCX is INTEGER !> storage spacing between elements of DX !>
[in,out]	DY	!> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) ) !>
[in]	INCY	!> INCY is INTEGER !> storage spacing between elements of DY !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

!>
!>     jack dongarra, linpack, 3/11/78.
!>     modified 12/3/93, array(1) declarations changed to array(*)
!> 

Definition at line 81 of file dswap.f.

*
*  -- 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,INCY,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DX(*),DY(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION DTEMP
      INTEGER I,IX,IY,M,MP1
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC mod
*     ..
      IF (n.LE.0) RETURN
      IF (incx.EQ.1 .AND. incy.EQ.1) THEN
*
*       code for both increments equal to 1
*
*
*       clean-up loop
*
         m = mod(n,3)
         IF (m.NE.0) THEN
            DO i = 1,m
               dtemp = dx(i)
               dx(i) = dy(i)
               dy(i) = dtemp
            END DO
            IF (n.LT.3) RETURN
         END IF
         mp1 = m + 1
         DO i = mp1,n,3
            dtemp = dx(i)
            dx(i) = dy(i)
            dy(i) = dtemp
            dtemp = dx(i+1)
            dx(i+1) = dy(i+1)
            dy(i+1) = dtemp
            dtemp = dx(i+2)
            dx(i+2) = dy(i+2)
            dy(i+2) = dtemp
         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
            dtemp = dx(ix)
            dx(ix) = dy(iy)
            dy(iy) = dtemp
            ix = ix + incx
            iy = iy + incy
         END DO
      END IF
      RETURN
*
*     End of DSWAP
*

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