1      subroutine  drot (n,dx,incx,dy,incy,c,s)
2c
3c     applies a plane rotation.
4c     jack dongarra, linpack, 3/11/78.
5c     modified 12/3/93, array(1) declarations changed to array(*)
6c
7      double precision dx(*),dy(*),dtemp,c,s
8      integer i,incx,incy,ix,iy,n
9c
10      if(n.le.0)return
11      if(incx.eq.1.and.incy.eq.1)go to 20
12c
13c       code for unequal increments or equal increments not equal
14c         to 1
15c
16      ix = 1
17      iy = 1
18      if(incx.lt.0)ix = (-n+1)*incx + 1
19      if(incy.lt.0)iy = (-n+1)*incy + 1
20      do 10 i = 1,n
21        dtemp = c*dx(ix) + s*dy(iy)
22        dy(iy) = c*dy(iy) - s*dx(ix)
23        dx(ix) = dtemp
24        ix = ix + incx
25        iy = iy + incy
26   10 continue
27      return
28c
29c       code for both increments equal to 1
30c
31   20 do 30 i = 1,n
32        dtemp = c*dx(i) + s*dy(i)
33        dy(i) = c*dy(i) - s*dx(i)
34        dx(i) = dtemp
35   30 continue
36      return
37      end
38