root / src / blas / srotg.f @ 7
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SUBROUTINE SROTG(SA,SB,C,S) |
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* .. Scalar Arguments .. |
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REAL C,S,SA,SB |
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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 givens plane rotation. |
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* jack dongarra, linpack, 3/11/78. |
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* |
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* |
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* .. Local Scalars .. |
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REAL R,ROE,SCALE,Z |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC ABS,SIGN,SQRT |
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* .. |
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ROE = SB |
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IF (ABS(SA).GT.ABS(SB)) ROE = SA |
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SCALE = ABS(SA) + ABS(SB) |
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IF (SCALE.NE.0.0) GO TO 10 |
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C = 1.0 |
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S = 0.0 |
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R = 0.0 |
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Z = 0.0 |
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GO TO 20 |
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10 R = SCALE*SQRT((SA/SCALE)**2+ (SB/SCALE)**2) |
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R = SIGN(1.0,ROE)*R |
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C = SA/R |
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S = SB/R |
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Z = 1.0 |
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IF (ABS(SA).GT.ABS(SB)) Z = S |
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IF (ABS(SB).GE.ABS(SA) .AND. C.NE.0.0) Z = 1.0/C |
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20 SA = R |
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SB = Z |
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RETURN |
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END |