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https://gitlab.com/libeigen/eigen.git
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209 lines
4.7 KiB
FortranFixed
209 lines
4.7 KiB
FortranFixed
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SUBROUTINE SROTMG(SD1,SD2,SX1,SY1,SPARAM)
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* .. Scalar Arguments ..
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REAL SD1,SD2,SX1,SY1
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* ..
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* .. Array Arguments ..
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REAL SPARAM(5)
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* ..
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*
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* Purpose
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* =======
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*
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* CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
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* THE SECOND COMPONENT OF THE 2-VECTOR (SQRT(SD1)*SX1,SQRT(SD2)*
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* SY2)**T.
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* WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
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*
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* SFLAG=-1.E0 SFLAG=0.E0 SFLAG=1.E0 SFLAG=-2.E0
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*
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* (SH11 SH12) (1.E0 SH12) (SH11 1.E0) (1.E0 0.E0)
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* H=( ) ( ) ( ) ( )
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* (SH21 SH22), (SH21 1.E0), (-1.E0 SH22), (0.E0 1.E0).
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* LOCATIONS 2-4 OF SPARAM CONTAIN SH11,SH21,SH12, AND SH22
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* RESPECTIVELY. (VALUES OF 1.E0, -1.E0, OR 0.E0 IMPLIED BY THE
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* VALUE OF SPARAM(1) ARE NOT STORED IN SPARAM.)
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*
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* THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
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* INEXACT. THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
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* OF SD1 AND SD2. ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
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*
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*
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* Arguments
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* =========
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*
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*
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* SD1 (input/output) REAL
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*
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* SD2 (input/output) REAL
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*
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* SX1 (input/output) REAL
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*
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* SY1 (input) REAL
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*
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*
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* SPARAM (input/output) REAL array, dimension 5
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* SPARAM(1)=SFLAG
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* SPARAM(2)=SH11
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* SPARAM(3)=SH21
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* SPARAM(4)=SH12
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* SPARAM(5)=SH22
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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REAL GAM,GAMSQ,ONE,RGAMSQ,SFLAG,SH11,SH12,SH21,SH22,SP1,SP2,SQ1,
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+ SQ2,STEMP,SU,TWO,ZERO
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INTEGER IGO
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS
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* ..
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* .. Data statements ..
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*
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DATA ZERO,ONE,TWO/0.E0,1.E0,2.E0/
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DATA GAM,GAMSQ,RGAMSQ/4096.E0,1.67772E7,5.96046E-8/
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* ..
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IF (.NOT.SD1.LT.ZERO) GO TO 10
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* GO ZERO-H-D-AND-SX1..
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GO TO 60
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10 CONTINUE
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* CASE-SD1-NONNEGATIVE
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SP2 = SD2*SY1
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IF (.NOT.SP2.EQ.ZERO) GO TO 20
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SFLAG = -TWO
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GO TO 260
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* REGULAR-CASE..
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20 CONTINUE
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SP1 = SD1*SX1
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SQ2 = SP2*SY1
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SQ1 = SP1*SX1
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*
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IF (.NOT.ABS(SQ1).GT.ABS(SQ2)) GO TO 40
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SH21 = -SY1/SX1
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SH12 = SP2/SP1
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*
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SU = ONE - SH12*SH21
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*
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IF (.NOT.SU.LE.ZERO) GO TO 30
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* GO ZERO-H-D-AND-SX1..
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GO TO 60
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30 CONTINUE
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SFLAG = ZERO
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SD1 = SD1/SU
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SD2 = SD2/SU
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SX1 = SX1*SU
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* GO SCALE-CHECK..
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GO TO 100
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40 CONTINUE
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IF (.NOT.SQ2.LT.ZERO) GO TO 50
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* GO ZERO-H-D-AND-SX1..
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GO TO 60
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50 CONTINUE
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SFLAG = ONE
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SH11 = SP1/SP2
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SH22 = SX1/SY1
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SU = ONE + SH11*SH22
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STEMP = SD2/SU
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SD2 = SD1/SU
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SD1 = STEMP
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SX1 = SY1*SU
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* GO SCALE-CHECK
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GO TO 100
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* PROCEDURE..ZERO-H-D-AND-SX1..
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60 CONTINUE
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SFLAG = -ONE
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SH11 = ZERO
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SH12 = ZERO
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SH21 = ZERO
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SH22 = ZERO
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*
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SD1 = ZERO
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SD2 = ZERO
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SX1 = ZERO
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* RETURN..
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GO TO 220
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* PROCEDURE..FIX-H..
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70 CONTINUE
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IF (.NOT.SFLAG.GE.ZERO) GO TO 90
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*
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IF (.NOT.SFLAG.EQ.ZERO) GO TO 80
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SH11 = ONE
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SH22 = ONE
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SFLAG = -ONE
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GO TO 90
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80 CONTINUE
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SH21 = -ONE
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SH12 = ONE
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SFLAG = -ONE
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90 CONTINUE
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GO TO IGO(120,150,180,210)
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* PROCEDURE..SCALE-CHECK
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100 CONTINUE
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110 CONTINUE
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IF (.NOT.SD1.LE.RGAMSQ) GO TO 130
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IF (SD1.EQ.ZERO) GO TO 160
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ASSIGN 120 TO IGO
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* FIX-H..
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GO TO 70
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120 CONTINUE
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SD1 = SD1*GAM**2
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SX1 = SX1/GAM
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SH11 = SH11/GAM
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SH12 = SH12/GAM
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GO TO 110
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130 CONTINUE
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140 CONTINUE
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IF (.NOT.SD1.GE.GAMSQ) GO TO 160
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ASSIGN 150 TO IGO
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* FIX-H..
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GO TO 70
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150 CONTINUE
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SD1 = SD1/GAM**2
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SX1 = SX1*GAM
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SH11 = SH11*GAM
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SH12 = SH12*GAM
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GO TO 140
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160 CONTINUE
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170 CONTINUE
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IF (.NOT.ABS(SD2).LE.RGAMSQ) GO TO 190
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IF (SD2.EQ.ZERO) GO TO 220
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ASSIGN 180 TO IGO
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* FIX-H..
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GO TO 70
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180 CONTINUE
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SD2 = SD2*GAM**2
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SH21 = SH21/GAM
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SH22 = SH22/GAM
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GO TO 170
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190 CONTINUE
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200 CONTINUE
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IF (.NOT.ABS(SD2).GE.GAMSQ) GO TO 220
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ASSIGN 210 TO IGO
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* FIX-H..
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GO TO 70
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210 CONTINUE
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SD2 = SD2/GAM**2
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SH21 = SH21*GAM
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SH22 = SH22*GAM
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GO TO 200
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220 CONTINUE
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IF (SFLAG) 250,230,240
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230 CONTINUE
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SPARAM(3) = SH21
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SPARAM(4) = SH12
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GO TO 260
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240 CONTINUE
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SPARAM(2) = SH11
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SPARAM(5) = SH22
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GO TO 260
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250 CONTINUE
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SPARAM(2) = SH11
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SPARAM(3) = SH21
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SPARAM(4) = SH12
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SPARAM(5) = SH22
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260 CONTINUE
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SPARAM(1) = SFLAG
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RETURN
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END
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