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C ddot.f |
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C is freely available from netlib. It is not subject to any GNU License |
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C set by the authors of the ASCEND math programming system. |
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C $Date: 1996/04/30 18:14:07 $ $Revision: 1.1.1.1 $ |
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C |
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double precision function ddot(n,dx,incx,dy,incy) |
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c |
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c forms the dot product of two vectors. |
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c uses unrolled loops for increments equal to one. |
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c jack dongarra, linpack, 3/11/78. |
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c |
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double precision dx(*),dy(*),dtemp |
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integer i,incx,incy,ix,iy,m,mp1,n |
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c |
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ddot = 0.0d0 |
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dtemp = 0.0d0 |
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if(n.le.0)return |
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if(incx.eq.1.and.incy.eq.1)go to 20 |
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c |
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c code for unequal increments or equal increments |
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c not equal to 1 |
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c |
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ix = 1 |
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iy = 1 |
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if(incx.lt.0)ix = (-n+1)*incx + 1 |
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if(incy.lt.0)iy = (-n+1)*incy + 1 |
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do 10 i = 1,n |
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dtemp = dtemp + dx(ix)*dy(iy) |
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ix = ix + incx |
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iy = iy + incy |
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10 continue |
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ddot = dtemp |
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return |
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c |
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c code for both increments equal to 1 |
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c |
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c |
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c clean-up loop |
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c |
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20 m = mod(n,5) |
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if( m .eq. 0 ) go to 40 |
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do 30 i = 1,m |
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dtemp = dtemp + dx(i)*dy(i) |
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30 continue |
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if( n .lt. 5 ) go to 60 |
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40 mp1 = m + 1 |
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do 50 i = mp1,n,5 |
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dtemp = dtemp + dx(i)*dy(i) + dx(i + 1)*dy(i + 1) + |
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* dx(i + 2)*dy(i + 2) + dx(i + 3)*dy(i + 3) + dx(i + 4)*dy(i + 4) |
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50 continue |
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60 ddot = dtemp |
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return |
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end |
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