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SUBROUTINE DROTMG(DD1,DD2,DX1,DY1,DPARAM) |
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* .. Scalar Arguments .. |
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DOUBLE PRECISION DD1,DD2,DX1,DY1 |
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* .. |
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* .. Array Arguments .. |
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DOUBLE PRECISION DPARAM(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 (DSQRT(DD1)*DX1,DSQRT(DD2)* |
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* DY2)**T. |
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* WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS.. |
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* |
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* DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0 |
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* |
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* (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0) |
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* H=( ) ( ) ( ) ( ) |
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* (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0). |
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* LOCATIONS 2-4 OF DPARAM CONTAIN DH11, DH21, DH12, AND DH22 |
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* RESPECTIVELY. (VALUES OF 1.D0, -1.D0, OR 0.D0 IMPLIED BY THE |
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* VALUE OF DPARAM(1) ARE NOT STORED IN DPARAM.) |
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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 DD1 AND DD2. 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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* DD1 (input/output) DOUBLE PRECISION |
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* |
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* DD2 (input/output) DOUBLE PRECISION |
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* |
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* DX1 (input/output) DOUBLE PRECISION |
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* |
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* DY1 (input) DOUBLE PRECISION |
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* |
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* DPARAM (input/output) DOUBLE PRECISION array, dimension 5 |
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* DPARAM(1)=DFLAG |
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* DPARAM(2)=DH11 |
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* DPARAM(3)=DH21 |
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* DPARAM(4)=DH12 |
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* DPARAM(5)=DH22 |
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* |
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* ===================================================================== |
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* |
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* .. Local Scalars .. |
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DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,DP1,DP2,DQ1,DQ2,DTEMP, |
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+ DU,GAM,GAMSQ,ONE,RGAMSQ,TWO,ZERO |
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INTEGER IGO |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC DABS |
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* .. |
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* .. Data statements .. |
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* |
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DATA ZERO,ONE,TWO/0.D0,1.D0,2.D0/ |
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DATA GAM,GAMSQ,RGAMSQ/4096.D0,16777216.D0,5.9604645D-8/ |
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* .. |
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|
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IF (.NOT.DD1.LT.ZERO) GO TO 10 |
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* GO ZERO-H-D-AND-DX1.. |
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GO TO 60 |
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10 CONTINUE |
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* CASE-DD1-NONNEGATIVE |
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DP2 = DD2*DY1 |
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IF (.NOT.DP2.EQ.ZERO) GO TO 20 |
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DFLAG = -TWO |
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GO TO 260 |
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* REGULAR-CASE.. |
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20 CONTINUE |
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DP1 = DD1*DX1 |
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DQ2 = DP2*DY1 |
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DQ1 = DP1*DX1 |
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* |
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IF (.NOT.DABS(DQ1).GT.DABS(DQ2)) GO TO 40 |
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DH21 = -DY1/DX1 |
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DH12 = DP2/DP1 |
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* |
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DU = ONE - DH12*DH21 |
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* |
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IF (.NOT.DU.LE.ZERO) GO TO 30 |
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* GO ZERO-H-D-AND-DX1.. |
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GO TO 60 |
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30 CONTINUE |
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DFLAG = ZERO |
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DD1 = DD1/DU |
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DD2 = DD2/DU |
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DX1 = DX1*DU |
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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.DQ2.LT.ZERO) GO TO 50 |
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* GO ZERO-H-D-AND-DX1.. |
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GO TO 60 |
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50 CONTINUE |
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DFLAG = ONE |
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DH11 = DP1/DP2 |
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DH22 = DX1/DY1 |
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DU = ONE + DH11*DH22 |
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DTEMP = DD2/DU |
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DD2 = DD1/DU |
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DD1 = DTEMP |
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DX1 = DY1*DU |
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* GO SCALE-CHECK |
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GO TO 100 |
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* PROCEDURE..ZERO-H-D-AND-DX1.. |
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60 CONTINUE |
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DFLAG = -ONE |
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DH11 = ZERO |
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DH12 = ZERO |
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DH21 = ZERO |
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DH22 = ZERO |
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* |
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DD1 = ZERO |
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DD2 = ZERO |
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DX1 = 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.DFLAG.GE.ZERO) GO TO 90 |
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* |
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IF (.NOT.DFLAG.EQ.ZERO) GO TO 80 |
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DH11 = ONE |
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DH22 = ONE |
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DFLAG = -ONE |
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GO TO 90 |
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80 CONTINUE |
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DH21 = -ONE |
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DH12 = ONE |
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DFLAG = -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.DD1.LE.RGAMSQ) GO TO 130 |
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IF (DD1.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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DD1 = DD1*GAM**2 |
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DX1 = DX1/GAM |
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DH11 = DH11/GAM |
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DH12 = DH12/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.DD1.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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DD1 = DD1/GAM**2 |
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DX1 = DX1*GAM |
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DH11 = DH11*GAM |
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DH12 = DH12*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.DABS(DD2).LE.RGAMSQ) GO TO 190 |
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IF (DD2.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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DD2 = DD2*GAM**2 |
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DH21 = DH21/GAM |
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DH22 = DH22/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.DABS(DD2).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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DD2 = DD2/GAM**2 |
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DH21 = DH21*GAM |
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DH22 = DH22*GAM |
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GO TO 200 |
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220 CONTINUE |
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IF (DFLAG) 250,230,240 |
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230 CONTINUE |
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DPARAM(3) = DH21 |
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DPARAM(4) = DH12 |
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GO TO 260 |
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240 CONTINUE |
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DPARAM(2) = DH11 |
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DPARAM(5) = DH22 |
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GO TO 260 |
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250 CONTINUE |
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DPARAM(2) = DH11 |
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DPARAM(3) = DH21 |
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DPARAM(4) = DH12 |
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DPARAM(5) = DH22 |
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260 CONTINUE |
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DPARAM(1) = DFLAG |
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RETURN |
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END |