| 1 | DOUBLE PRECISION FUNCTION DSDOT(N,SX,INCX,SY,INCY) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | INTEGER INCX,INCY,N |
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| 4 | * .. |
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| 5 | * .. Array Arguments .. |
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| 6 | REAL SX(*),SY(*) |
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| 7 | * .. |
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| 8 | * |
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| 9 | * AUTHORS |
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| 10 | * ======= |
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| 11 | * Lawson, C. L., (JPL), Hanson, R. J., (SNLA), |
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| 12 | * Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL) |
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| 13 | * |
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| 14 | * Purpose |
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| 15 | * ======= |
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| 16 | * Compute the inner product of two vectors with extended |
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| 17 | * precision accumulation and result. |
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| 18 | * |
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| 19 | * Returns D.P. dot product accumulated in D.P., for S.P. SX and SY |
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| 20 | * DSDOT = sum for I = 0 to N-1 of SX(LX+I*INCX) * SY(LY+I*INCY), |
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| 21 | * where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is |
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| 22 | * defined in a similar way using INCY. |
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| 23 | * |
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| 24 | * Arguments |
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| 25 | * ========= |
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| 26 | * |
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| 27 | * N (input) INTEGER |
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| 28 | * number of elements in input vector(s) |
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| 29 | * |
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| 30 | * SX (input) REAL array, dimension(N) |
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| 31 | * single precision vector with N elements |
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| 32 | * |
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| 33 | * INCX (input) INTEGER |
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| 34 | * storage spacing between elements of SX |
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| 35 | * |
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| 36 | * SY (input) REAL array, dimension(N) |
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| 37 | * single precision vector with N elements |
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| 38 | * |
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| 39 | * INCY (input) INTEGER |
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| 40 | * storage spacing between elements of SY |
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| 41 | * |
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| 42 | * DSDOT (output) DOUBLE PRECISION |
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| 43 | * DSDOT double precision dot product (zero if N.LE.0) |
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| 44 | * |
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| 45 | * REFERENCES |
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| 46 | * ========== |
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| 47 | * |
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| 48 | * C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T. |
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| 49 | * Krogh, Basic linear algebra subprograms for Fortran |
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| 50 | * usage, Algorithm No. 539, Transactions on Mathematical |
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| 51 | * Software 5, 3 (September 1979), pp. 308-323. |
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| 52 | * |
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| 53 | * REVISION HISTORY (YYMMDD) |
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| 54 | * ========================== |
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| 55 | * |
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| 56 | * 791001 DATE WRITTEN |
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| 57 | * 890831 Modified array declarations. (WRB) |
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| 58 | * 890831 REVISION DATE from Version 3.2 |
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| 59 | * 891214 Prologue converted to Version 4.0 format. (BAB) |
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| 60 | * 920310 Corrected definition of LX in DESCRIPTION. (WRB) |
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| 61 | * 920501 Reformatted the REFERENCES section. (WRB) |
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| 62 | * 070118 Reformat to LAPACK style (JL) |
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| 63 | * |
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| 64 | * ===================================================================== |
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| 65 | * |
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| 66 | * .. Local Scalars .. |
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| 67 | INTEGER I,KX,KY,NS |
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| 68 | * .. |
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| 69 | * .. Intrinsic Functions .. |
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| 70 | INTRINSIC DBLE |
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| 71 | * .. |
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| 72 | DSDOT = 0.0D0 |
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| 73 | IF (N.LE.0) RETURN |
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| 74 | IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 20 |
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| 75 | * |
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| 76 | * Code for unequal or nonpositive increments. |
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| 77 | * |
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| 78 | KX = 1 |
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| 79 | KY = 1 |
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| 80 | IF (INCX.LT.0) KX = 1 + (1-N)*INCX |
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| 81 | IF (INCY.LT.0) KY = 1 + (1-N)*INCY |
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| 82 | DO 10 I = 1,N |
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| 83 | DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY)) |
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| 84 | KX = KX + INCX |
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| 85 | KY = KY + INCY |
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| 86 | 10 CONTINUE |
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| 87 | RETURN |
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| 88 | * |
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| 89 | * Code for equal, positive, non-unit increments. |
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| 90 | * |
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| 91 | 20 NS = N*INCX |
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| 92 | DO 30 I = 1,NS,INCX |
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| 93 | DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I)) |
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| 94 | 30 CONTINUE |
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| 95 | RETURN |
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| 96 | END |
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