LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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ddot.f
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1*> \brief \b DDOT
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8* Definition:
9* ===========
10*
11* DOUBLE PRECISION FUNCTION DDOT(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*> DDOT forms the dot product of two vectors.
27*> uses unrolled loops for increments equal to one.
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] 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] 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 DOUBLE PRECISION FUNCTION ddot(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 ddot = 0.0d0
104 dtemp = 0.0d0
105 IF (n.LE.0) RETURN
106 IF (incx.EQ.1 .AND. incy.EQ.1) THEN
107*
108* code for both increments equal to 1
109*
110*
111* clean-up loop
112*
113 m = mod(n,5)
114 IF (m.NE.0) THEN
115 DO i = 1,m
116 dtemp = dtemp + dx(i)*dy(i)
117 END DO
118 IF (n.LT.5) THEN
119 ddot=dtemp
120 RETURN
121 END IF
122 END IF
123 mp1 = m + 1
124 DO i = mp1,n,5
125 dtemp = dtemp + dx(i)*dy(i) + dx(i+1)*dy(i+1) +
126 \$ dx(i+2)*dy(i+2) + dx(i+3)*dy(i+3) + dx(i+4)*dy(i+4)
127 END DO
128 ELSE
129*
130* code for unequal increments or equal increments
131* not equal to 1
132*
133 ix = 1
134 iy = 1
135 IF (incx.LT.0) ix = (-n+1)*incx + 1
136 IF (incy.LT.0) iy = (-n+1)*incy + 1
137 DO i = 1,n
138 dtemp = dtemp + dx(ix)*dy(iy)
139 ix = ix + incx
140 iy = iy + incy
141 END DO
142 END IF
143 ddot = dtemp
144 RETURN
145*
146* End of DDOT
147*
148 END
double precision function ddot(N, DX, INCX, DY, INCY)
DDOT
Definition: ddot.f:82