Statistiques
| Révision :

root / src / blas / dsdot.f @ 4

Historique | Voir | Annoter | Télécharger (2,6 ko)

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