drotg()

subroutine drotg	(	double precision	DA,
		double precision	DB,
		double precision	C,
		double precision	S
	)

DROTG

Purpose:

    DROTG construct givens plane rotation.

Parameters

[in]	DA	DA is DOUBLE PRECISION
[in]	DB	DB is DOUBLE PRECISION
[out]	C	C is DOUBLE PRECISION
[out]	S	S is DOUBLE PRECISION

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date

November 2017

Further Details:

     jack dongarra, linpack, 3/11/78.

Definition at line 71 of file drotg.f.

*
*  -- Reference BLAS level1 routine (version 3.8.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2017
*
*     .. Scalar Arguments ..
      DOUBLE PRECISION C,DA,DB,S
*     ..
*
*  =====================================================================
*
*     .. 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.EQ.0.0d0) THEN
         c = 1.0d0
         s = 0.0d0
         r = 0.0d0
         z = 0.0d0
      ELSE
         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
      END IF
      da = r
      db = z
      RETURN

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