dsdot.f.html

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<pre>
      DOUBLE PRECISION FUNCTION <a name="DSDOT.1"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a>(N,SX,INCX,SY,INCY)
<span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      INTEGER INCX,INCY,N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      REAL SX(*),SY(*)
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  AUTHORS
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">  Lawson, C. L., (JPL), Hanson, R. J., (SNLA), 
</span><span class="comment">*</span><span class="comment">  Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">  Compute the inner product of two vectors with extended
</span><span class="comment">*</span><span class="comment">  precision accumulation and result.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Returns D.P. dot product accumulated in D.P., for S.P. SX and SY
</span><span class="comment">*</span><span class="comment">  <a name="DSDOT.20"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> = sum for I = 0 to N-1 of  SX(LX+I*INCX) * SY(LY+I*INCY),
</span><span class="comment">*</span><span class="comment">  where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
</span><span class="comment">*</span><span class="comment">  defined in a similar way using INCY.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N      (input) INTEGER
</span><span class="comment">*</span><span class="comment">         number of elements in input vector(s)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  SX     (input) REAL array, dimension(N)
</span><span class="comment">*</span><span class="comment">         single precision vector with N elements
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCX   (input) INTEGER
</span><span class="comment">*</span><span class="comment">          storage spacing between elements of SX
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  SY     (input) REAL array, dimension(N)
</span><span class="comment">*</span><span class="comment">         single precision vector with N elements
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCY   (input) INTEGER
</span><span class="comment">*</span><span class="comment">         storage spacing between elements of SY
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="DSDOT.42"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a>  (output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment">         <a name="DSDOT.43"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a>  double precision dot product (zero if N.LE.0)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  REFERENCES
</span><span class="comment">*</span><span class="comment">  ==========
</span><span class="comment">*</span><span class="comment">      
</span><span class="comment">*</span><span class="comment">  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
</span><span class="comment">*</span><span class="comment">  Krogh, Basic linear algebra subprograms for Fortran
</span><span class="comment">*</span><span class="comment">  usage, Algorithm No. 539, Transactions on Mathematical
</span><span class="comment">*</span><span class="comment">  Software 5, 3 (September 1979), pp. 308-323.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  REVISION HISTORY  (YYMMDD)
</span><span class="comment">*</span><span class="comment">  ==========================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  791001  DATE WRITTEN
</span><span class="comment">*</span><span class="comment">  890831  Modified array declarations.  (WRB)
</span><span class="comment">*</span><span class="comment">  890831  REVISION DATE from Version 3.2
</span><span class="comment">*</span><span class="comment">  891214  Prologue converted to Version 4.0 format.  (BAB)
</span><span class="comment">*</span><span class="comment">  920310  Corrected definition of LX in DESCRIPTION.  (WRB)
</span><span class="comment">*</span><span class="comment">  920501  Reformatted the REFERENCES section.  (WRB)
</span><span class="comment">*</span><span class="comment">  070118  Reformat to LAPACK style (JL)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER I,KX,KY,NS
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC DBLE
<span class="comment">*</span><span class="comment">     ..
</span>      <a name="DSDOT.72"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> = 0.0D0
      IF (N.LE.0) RETURN
      IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 20
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Code for unequal or nonpositive increments.
</span><span class="comment">*</span><span class="comment">
</span>      KX = 1
      KY = 1
      IF (INCX.LT.0) KX = 1 + (1-N)*INCX
      IF (INCY.LT.0) KY = 1 + (1-N)*INCY
      DO 10 I = 1,N
          <a name="DSDOT.83"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> = <a name="DSDOT.83"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> + DBLE(SX(KX))*DBLE(SY(KY))
          KX = KX + INCX
          KY = KY + INCY
   10 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Code for equal, positive, non-unit increments.
</span><span class="comment">*</span><span class="comment">
</span>   20 NS = N*INCX
      DO 30 I = 1,NS,INCX
          <a name="DSDOT.93"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> = <a name="DSDOT.93"></a><a href="dsdot.f.html#DSDOT.1">DSDOT</a> + DBLE(SX(I))*DBLE(SY(I))
   30 CONTINUE
      RETURN
      END

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