.TH ZROTG 3 "16 October 1992" "BLAS routine" "BLAS routine"
.SH NAME
ZROTG - construct givens plane rotation
.SH SYNOPSIS
.TP 28
subroutine zrotg(ca,cb,c,s)
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double
complex ca,cb,s
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double
precision c
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double
precision norm,scale
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double
complex alpha
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if
(cdabs(ca) .ne. 0.0d0) go to 10
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c
= 0.0d0
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s
= (1.0d0,0.0d0)
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ca
= cb
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go
to 20
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10
continue
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scale
= cdabs(ca) + cdabs(cb)
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norm
= scale*dsqrt((cdabs(ca/dcmplx(scale,0.0d0)))**2 +
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*
(cdabs(cb/dcmplx(scale,0.0d0)))**2)
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alpha
= ca /cdabs(ca)
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c
= cdabs(ca) / norm
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s
= alpha * dconjg(cb) / norm
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ca
= alpha * norm
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20
continue
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return
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end
.SH PURPOSE