/[ascend]/trunk/blas/ddot.f
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Annotation of /trunk/blas/ddot.f

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Fri Oct 29 20:54:12 2004 UTC (17 years, 11 months ago) by aw0a
File size: 1388 byte(s)
Setting up web subdirectory in repository
1 aw0a 1 C ddot.f
2     C is freely available from netlib. It is not subject to any GNU License
3     C set by the authors of the ASCEND math programming system.
4     C $Date: 1996/04/30 18:14:07 $ $Revision: 1.1.1.1 $
5     C
6     double precision function ddot(n,dx,incx,dy,incy)
7     c
8     c forms the dot product of two vectors.
9     c uses unrolled loops for increments equal to one.
10     c jack dongarra, linpack, 3/11/78.
11     c
12     double precision dx(*),dy(*),dtemp
13     integer i,incx,incy,ix,iy,m,mp1,n
14     c
15     ddot = 0.0d0
16     dtemp = 0.0d0
17     if(n.le.0)return
18     if(incx.eq.1.and.incy.eq.1)go to 20
19     c
20     c code for unequal increments or equal increments
21     c not equal to 1
22     c
23     ix = 1
24     iy = 1
25     if(incx.lt.0)ix = (-n+1)*incx + 1
26     if(incy.lt.0)iy = (-n+1)*incy + 1
27     do 10 i = 1,n
28     dtemp = dtemp + dx(ix)*dy(iy)
29     ix = ix + incx
30     iy = iy + incy
31     10 continue
32     ddot = dtemp
33     return
34     c
35     c code for both increments equal to 1
36     c
37     c
38     c clean-up loop
39     c
40     20 m = mod(n,5)
41     if( m .eq. 0 ) go to 40
42     do 30 i = 1,m
43     dtemp = dtemp + dx(i)*dy(i)
44     30 continue
45     if( n .lt. 5 ) go to 60
46     40 mp1 = m + 1
47     do 50 i = mp1,n,5
48     dtemp = dtemp + dx(i)*dy(i) + dx(i + 1)*dy(i + 1) +
49     * dx(i + 2)*dy(i + 2) + dx(i + 3)*dy(i + 3) + dx(i + 4)*dy(i + 4)
50     50 continue
51     60 ddot = dtemp
52     return
53     end
54    
55    

john.pye@anu.edu.au
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