root / src / blas / zrotg.f @ 5
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SUBROUTINE ZROTG(CA,CB,C,S) |
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* .. Scalar Arguments .. |
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DOUBLE COMPLEX CA,CB,S |
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DOUBLE PRECISION C |
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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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* determines a double complex Givens rotation. |
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* |
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* .. Local Scalars .. |
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DOUBLE COMPLEX ALPHA |
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DOUBLE PRECISION NORM,SCALE |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT |
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* .. |
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IF (CDABS(CA).NE.0.0d0) GO TO 10 |
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C = 0.0d0 |
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S = (1.0d0,0.0d0) |
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CA = CB |
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GO TO 20 |
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10 CONTINUE |
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SCALE = CDABS(CA) + CDABS(CB) |
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NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+ |
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+ (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2) |
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ALPHA = CA/CDABS(CA) |
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C = CDABS(CA)/NORM |
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S = ALPHA*DCONJG(CB)/NORM |
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CA = ALPHA*NORM |
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20 CONTINUE |
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RETURN |
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END |