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SUBROUTINE DROTG(DA,DB,C,S)
* .. Scalar Arguments ..
DOUBLE PRECISION C,DA,DB,S
* ..
*
* Purpose
* =======
*
* construct givens plane rotation.
* jack dongarra, linpack, 3/11/78.
*
*
* .. Local Scalars ..
DOUBLE PRECISION R,ROE,SCALE,Z
* ..
* .. Intrinsic Functions ..
INTRINSIC DABS,DSIGN,DSQRT
* ..
ROE = DB
IF (DABS(DA).GT.DABS(DB)) ROE = DA
SCALE = DABS(DA) + DABS(DB)
IF (SCALE.NE.0.0d0) GO TO 10
C = 1.0d0
S = 0.0d0
R = 0.0d0
Z = 0.0d0
GO TO 20
10 R = SCALE*DSQRT((DA/SCALE)**2+ (DB/SCALE)**2)
R = DSIGN(1.0d0,ROE)*R
C = DA/R
S = DB/R
Z = 1.0d0
IF (DABS(DA).GT.DABS(DB)) Z = S
IF (DABS(DB).GE.DABS(DA) .AND. C.NE.0.0d0) Z = 1.0d0/C
20 DA = R
DB = Z
RETURN
END
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