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SUBROUTINE SROTMG(SD1,SD2,SX1,SY1,SPARAM)
* .. Scalar Arguments ..
REAL SD1,SD2,SX1,SY1
* ..
* .. Array Arguments ..
REAL SPARAM(5)
* ..
*
* Purpose
* =======
*
* CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
* THE SECOND COMPONENT OF THE 2-VECTOR (SQRT(SD1)*SX1,SQRT(SD2)*
* SY2)**T.
* WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
*
* SFLAG=-1.E0 SFLAG=0.E0 SFLAG=1.E0 SFLAG=-2.E0
*
* (SH11 SH12) (1.E0 SH12) (SH11 1.E0) (1.E0 0.E0)
* H=( ) ( ) ( ) ( )
* (SH21 SH22), (SH21 1.E0), (-1.E0 SH22), (0.E0 1.E0).
* LOCATIONS 2-4 OF SPARAM CONTAIN SH11,SH21,SH12, AND SH22
* RESPECTIVELY. (VALUES OF 1.E0, -1.E0, OR 0.E0 IMPLIED BY THE
* VALUE OF SPARAM(1) ARE NOT STORED IN SPARAM.)
*
* THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
* INEXACT. THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
* OF SD1 AND SD2. ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
*
*
* Arguments
* =========
*
*
* SD1 (input/output) REAL
*
* SD2 (input/output) REAL
*
* SX1 (input/output) REAL
*
* SY1 (input) REAL
*
*
* SPARAM (input/output) REAL array, dimension 5
* SPARAM(1)=SFLAG
* SPARAM(2)=SH11
* SPARAM(3)=SH21
* SPARAM(4)=SH12
* SPARAM(5)=SH22
*
* =====================================================================
*
* .. Local Scalars ..
REAL GAM,GAMSQ,ONE,RGAMSQ,SFLAG,SH11,SH12,SH21,SH22,SP1,SP2,SQ1,
$ SQ2,STEMP,SU,TWO,ZERO
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS
* ..
* .. Data statements ..
*
DATA ZERO,ONE,TWO/0.E0,1.E0,2.E0/
DATA GAM,GAMSQ,RGAMSQ/4096.E0,1.67772E7,5.96046E-8/
* ..
IF (SD1.LT.ZERO) THEN
* GO ZERO-H-D-AND-SX1..
SFLAG = -ONE
SH11 = ZERO
SH12 = ZERO
SH21 = ZERO
SH22 = ZERO
*
SD1 = ZERO
SD2 = ZERO
SX1 = ZERO
ELSE
* CASE-SD1-NONNEGATIVE
SP2 = SD2*SY1
IF (SP2.EQ.ZERO) THEN
SFLAG = -TWO
SPARAM(1) = SFLAG
RETURN
END IF
* REGULAR-CASE..
SP1 = SD1*SX1
SQ2 = SP2*SY1
SQ1 = SP1*SX1
*
IF (ABS(SQ1).GT.ABS(SQ2)) THEN
SH21 = -SY1/SX1
SH12 = SP2/SP1
*
SU = ONE - SH12*SH21
*
IF (SU.GT.ZERO) THEN
SFLAG = ZERO
SD1 = SD1/SU
SD2 = SD2/SU
SX1 = SX1*SU
END IF
ELSE
IF (SQ2.LT.ZERO) THEN
* GO ZERO-H-D-AND-SX1..
SFLAG = -ONE
SH11 = ZERO
SH12 = ZERO
SH21 = ZERO
SH22 = ZERO
*
SD1 = ZERO
SD2 = ZERO
SX1 = ZERO
ELSE
SFLAG = ONE
SH11 = SP1/SP2
SH22 = SX1/SY1
SU = ONE + SH11*SH22
STEMP = SD2/SU
SD2 = SD1/SU
SD1 = STEMP
SX1 = SY1*SU
END IF
END IF
* PROCESURE..SCALE-CHECK
IF (SD1.NE.ZERO) THEN
DO WHILE ((SD1.LE.RGAMSQ) .OR. (SD1.GE.GAMSQ))
IF (SFLAG.EQ.ZERO) THEN
SH11 = ONE
SH22 = ONE
SFLAG = -ONE
ELSE
SH21 = -ONE
SH12 = ONE
SFLAG = -ONE
END IF
IF (SD1.LE.RGAMSQ) THEN
SD1 = SD1*GAM**2
SX1 = SX1/GAM
SH11 = SH11/GAM
SH12 = SH12/GAM
ELSE
SD1 = SD1/GAM**2
SX1 = SX1*GAM
SH11 = SH11*GAM
SH12 = SH12*GAM
END IF
ENDDO
END IF
IF (SD2.NE.ZERO) THEN
DO WHILE ( (ABS(SD2).LE.RGAMSQ) .OR. (ABS(SD2).GE.GAMSQ) )
IF (SFLAG.EQ.ZERO) THEN
SH11 = ONE
SH22 = ONE
SFLAG = -ONE
ELSE
SH21 = -ONE
SH12 = ONE
SFLAG = -ONE
END IF
IF (ABS(SD2).LE.RGAMSQ) THEN
SD2 = SD2*GAM**2
SH21 = SH21/GAM
SH22 = SH22/GAM
ELSE
SD2 = SD2/GAM**2
SH21 = SH21*GAM
SH22 = SH22*GAM
END IF
END DO
END IF
END IF
IF (SFLAG.LT.ZERO) THEN
SPARAM(2) = SH11
SPARAM(3) = SH21
SPARAM(4) = SH12
SPARAM(5) = SH22
ELSE IF (SFLAG.EQ.ZERO) THEN
SPARAM(3) = SH21
SPARAM(4) = SH12
ELSE
SPARAM(2) = SH11
SPARAM(5) = SH22
END IF
260 CONTINUE
SPARAM(1) = SFLAG
RETURN
END
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