man zrotg (Fonctions bibliothèques) - construct givens plane rotation
NAME
ZROTG - construct givens plane rotation
SYNOPSIS
- 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