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| 1 | SUBROUTINE DSCAL(N,DA,DX,INCX) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | DOUBLE PRECISION DA |
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| 4 | INTEGER INCX,N |
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| 5 | * .. |
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| 6 | * .. Array Arguments .. |
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| 7 | DOUBLE PRECISION DX(*) |
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| 8 | * .. |
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| 9 | * |
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| 10 | * Purpose |
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| 11 | * ======= |
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| 12 | ** |
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| 13 | * scales a vector by a constant. |
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| 14 | * uses unrolled loops for increment equal to one. |
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| 15 | * jack dongarra, linpack, 3/11/78. |
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| 16 | * modified 3/93 to return if incx .le. 0. |
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| 17 | * modified 12/3/93, array(1) declarations changed to array(*) |
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| 18 | * |
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| 19 | * |
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| 20 | * .. Local Scalars .. |
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| 21 | INTEGER I,M,MP1,NINCX |
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| 22 | * .. |
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| 23 | * .. Intrinsic Functions .. |
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| 24 | INTRINSIC MOD |
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| 25 | * .. |
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| 26 | IF (N.LE.0 .OR. INCX.LE.0) RETURN |
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| 27 | IF (INCX.EQ.1) GO TO 20 |
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| 28 | * |
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| 29 | * code for increment not equal to 1 |
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| 30 | * |
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| 31 | NINCX = N*INCX |
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| 32 | DO 10 I = 1,NINCX,INCX |
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| 33 | DX(I) = DA*DX(I) |
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| 34 | 10 CONTINUE |
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| 35 | RETURN |
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| 36 | * |
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| 37 | * code for increment equal to 1 |
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| 38 | * |
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| 39 | * |
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| 40 | * clean-up loop |
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| 41 | * |
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| 42 | 20 M = MOD(N,5) |
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| 43 | IF (M.EQ.0) GO TO 40 |
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| 44 | DO 30 I = 1,M |
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| 45 | DX(I) = DA*DX(I) |
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| 46 | 30 CONTINUE |
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| 47 | IF (N.LT.5) RETURN |
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| 48 | 40 MP1 = M + 1 |
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| 49 | DO 50 I = MP1,N,5 |
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| 50 | DX(I) = DA*DX(I) |
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| 51 | DX(I+1) = DA*DX(I+1) |
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| 52 | DX(I+2) = DA*DX(I+2) |
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| 53 | DX(I+3) = DA*DX(I+3) |
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| 54 | DX(I+4) = DA*DX(I+4) |
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| 55 | 50 CONTINUE |
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| 56 | RETURN |
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| 57 | END |
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