srotg()

subroutine srotg	(	real	SA,
		real	SB,
		real	C,
		real	S
	)

SROTG

Purpose:

    SROTG construct givens plane rotation.

Parameters

[in]	SA	SA is REAL
[in]	SB	SB is REAL
[out]	C	C is REAL
[out]	S	S is REAL

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 srotg.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 ..
      REAL C,S,SA,SB
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      REAL R,ROE,SCALE,Z
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC abs,sign,sqrt
*     ..
      roe = sb
      IF (abs(sa).GT.abs(sb)) roe = sa
      scale = abs(sa) + abs(sb)
      IF (scale.EQ.0.0) THEN
         c = 1.0
         s = 0.0
         r = 0.0
         z = 0.0
      ELSE
         r = scale*sqrt((sa/scale)**2+ (sb/scale)**2)
         r = sign(1.0,roe)*r
         c = sa/r
         s = sb/r
         z = 1.0
         IF (abs(sa).GT.abs(sb)) z = s
         IF (abs(sb).GE.abs(sa) .AND. c.NE.0.0) z = 1.0/c
      END IF
      sa = r
      sb = z
      RETURN

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