Construct givens plane rotation
subroutine zrotg(ca,cb,c,s)
double
complex ca,cb,s
double
precision c
double
precision norm,scale
double
complex alpha
if
(cdabs(ca) .ne. 0.0d0) go to 10
c
= 0.0d0
s
= (1.0d0,0.0d0)
ca
= cb
go
to 20
10
continue
scale
= cdabs(ca) + cdabs(cb)
norm
= scale*dsqrt((cdabs(ca/dcmplx(scale,0.0d0)))**2 +
*
(cdabs(cb/dcmplx(scale,0.0d0)))**2)
alpha
= ca /cdabs(ca)
c
= cdabs(ca) / norm
s
= alpha * dconjg(cb) / norm
ca
= alpha * norm
20
continue
return
end