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| 1 | SUBROUTINE SROTG(SA,SB,C,S) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | REAL C,S,SA,SB |
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| 4 | * .. |
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| 5 | * |
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| 6 | * Purpose |
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| 7 | * ======= |
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| 8 | * |
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| 9 | * construct givens plane rotation. |
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| 10 | * jack dongarra, linpack, 3/11/78. |
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| 11 | * |
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| 12 | * |
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| 13 | * .. Local Scalars .. |
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| 14 | REAL R,ROE,SCALE,Z |
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| 15 | * .. |
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| 16 | * .. Intrinsic Functions .. |
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| 17 | INTRINSIC ABS,SIGN,SQRT |
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| 18 | * .. |
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| 19 | ROE = SB |
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| 20 | IF (ABS(SA).GT.ABS(SB)) ROE = SA |
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| 21 | SCALE = ABS(SA) + ABS(SB) |
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| 22 | IF (SCALE.NE.0.0) GO TO 10 |
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| 23 | C = 1.0 |
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| 24 | S = 0.0 |
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| 25 | R = 0.0 |
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| 26 | Z = 0.0 |
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| 27 | GO TO 20 |
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| 28 | 10 R = SCALE*SQRT((SA/SCALE)**2+ (SB/SCALE)**2) |
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| 29 | R = SIGN(1.0,ROE)*R |
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| 30 | C = SA/R |
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| 31 | S = SB/R |
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| 32 | Z = 1.0 |
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| 33 | IF (ABS(SA).GT.ABS(SB)) Z = S |
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| 34 | IF (ABS(SB).GE.ABS(SA) .AND. C.NE.0.0) Z = 1.0/C |
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| 35 | 20 SA = R |
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| 36 | SB = Z |
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| 37 | RETURN |
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| 38 | END |
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