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| 1 | SUBROUTINE ZROTG(CA,CB,C,S) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | DOUBLE COMPLEX CA,CB,S |
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| 4 | DOUBLE PRECISION C |
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| 5 | * .. |
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| 6 | * |
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| 7 | * Purpose |
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| 8 | * ======= |
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| 9 | * |
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| 10 | * determines a double complex Givens rotation. |
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| 11 | * |
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| 12 | * .. Local Scalars .. |
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| 13 | DOUBLE COMPLEX ALPHA |
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| 14 | DOUBLE PRECISION NORM,SCALE |
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| 15 | * .. |
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| 16 | * .. Intrinsic Functions .. |
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| 17 | INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT |
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| 18 | * .. |
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| 19 | IF (CDABS(CA).NE.0.0d0) GO TO 10 |
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| 20 | C = 0.0d0 |
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| 21 | S = (1.0d0,0.0d0) |
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| 22 | CA = CB |
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| 23 | GO TO 20 |
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| 24 | 10 CONTINUE |
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| 25 | SCALE = CDABS(CA) + CDABS(CB) |
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| 26 | NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+ |
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| 27 | + (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2) |
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| 28 | ALPHA = CA/CDABS(CA) |
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| 29 | C = CDABS(CA)/NORM |
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| 30 | S = ALPHA*DCONJG(CB)/NORM |
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| 31 | CA = ALPHA*NORM |
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| 32 | 20 CONTINUE |
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| 33 | RETURN |
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| 34 | END |
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