LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
Searching...
No Matches
dswap.f
Go to the documentation of this file.
1*> \brief \b DSWAP
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8* Definition:
9* ===========
10*
11* SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
12*
13* .. Scalar Arguments ..
14* INTEGER INCX,INCY,N
15* ..
16* .. Array Arguments ..
17* DOUBLE PRECISION DX(*),DY(*)
18* ..
19*
20*
21*> \par Purpose:
22* =============
23*>
24*> \verbatim
25*>
26*> DSWAP interchanges two vectors.
27*> uses unrolled loops for increments equal to 1.
28*> \endverbatim
29*
30* Arguments:
31* ==========
32*
33*> \param[in] N
34*> \verbatim
35*> N is INTEGER
36*> number of elements in input vector(s)
37*> \endverbatim
38*>
39*> \param[in,out] DX
40*> \verbatim
41*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
42*> \endverbatim
43*>
44*> \param[in] INCX
45*> \verbatim
46*> INCX is INTEGER
47*> storage spacing between elements of DX
48*> \endverbatim
49*>
50*> \param[in,out] DY
51*> \verbatim
52*> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
53*> \endverbatim
54*>
55*> \param[in] INCY
56*> \verbatim
57*> INCY is INTEGER
58*> storage spacing between elements of DY
59*> \endverbatim
60*
61* Authors:
62* ========
63*
64*> \author Univ. of Tennessee
65*> \author Univ. of California Berkeley
66*> \author Univ. of Colorado Denver
67*> \author NAG Ltd.
68*
69*> \ingroup double_blas_level1
70*
71*> \par Further Details:
72* =====================
73*>
74*> \verbatim
75*>
76*> jack dongarra, linpack, 3/11/78.
77*> modified 12/3/93, array(1) declarations changed to array(*)
78*> \endverbatim
79*>
80* =====================================================================
81 SUBROUTINE dswap(N,DX,INCX,DY,INCY)
82*
83* -- Reference BLAS level1 routine --
84* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
85* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
86*
87* .. Scalar Arguments ..
88 INTEGER INCX,INCY,N
89* ..
90* .. Array Arguments ..
91 DOUBLE PRECISION DX(*),DY(*)
92* ..
93*
94* =====================================================================
95*
96* .. Local Scalars ..
97 DOUBLE PRECISION DTEMP
98 INTEGER I,IX,IY,M,MP1
99* ..
100* .. Intrinsic Functions ..
101 INTRINSIC mod
102* ..
103 IF (n.LE.0) RETURN
104 IF (incx.EQ.1 .AND. incy.EQ.1) THEN
105*
106* code for both increments equal to 1
107*
108*
109* clean-up loop
110*
111 m = mod(n,3)
112 IF (m.NE.0) THEN
113 DO i = 1,m
114 dtemp = dx(i)
115 dx(i) = dy(i)
116 dy(i) = dtemp
117 END DO
118 IF (n.LT.3) RETURN
119 END IF
120 mp1 = m + 1
121 DO i = mp1,n,3
122 dtemp = dx(i)
123 dx(i) = dy(i)
124 dy(i) = dtemp
125 dtemp = dx(i+1)
126 dx(i+1) = dy(i+1)
127 dy(i+1) = dtemp
128 dtemp = dx(i+2)
129 dx(i+2) = dy(i+2)
130 dy(i+2) = dtemp
131 END DO
132 ELSE
133*
134* code for unequal increments or equal increments not equal
135* to 1
136*
137 ix = 1
138 iy = 1
139 IF (incx.LT.0) ix = (-n+1)*incx + 1
140 IF (incy.LT.0) iy = (-n+1)*incy + 1
141 DO i = 1,n
142 dtemp = dx(ix)
143 dx(ix) = dy(iy)
144 dy(iy) = dtemp
145 ix = ix + incx
146 iy = iy + incy
147 END DO
148 END IF
149 RETURN
150*
151* End of DSWAP
152*
153 END
subroutine dswap(N, DX, INCX, DY, INCY)
DSWAP
Definition: dswap.f:82