root / src / blas / drotg.f @ 11
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SUBROUTINE DROTG(DA,DB,C,S) |
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* .. Scalar Arguments .. |
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DOUBLE PRECISION C,DA,DB,S |
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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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DOUBLE PRECISION R,ROE,SCALE,Z |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC DABS,DSIGN,DSQRT |
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* .. |
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ROE = DB |
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IF (DABS(DA).GT.DABS(DB)) ROE = DA |
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SCALE = DABS(DA) + DABS(DB) |
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IF (SCALE.NE.0.0d0) GO TO 10 |
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C = 1.0d0 |
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S = 0.0d0 |
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R = 0.0d0 |
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Z = 0.0d0 |
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GO TO 20 |
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10 R = SCALE*DSQRT((DA/SCALE)**2+ (DB/SCALE)**2) |
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R = DSIGN(1.0d0,ROE)*R |
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C = DA/R |
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S = DB/R |
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Z = 1.0d0 |
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IF (DABS(DA).GT.DABS(DB)) Z = S |
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IF (DABS(DB).GE.DABS(DA) .AND. C.NE.0.0d0) Z = 1.0d0/C |
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20 DA = R |
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DB = Z |
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RETURN |
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END |