sdsdot.f

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*> \brief \b SDSDOT
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*  Definition:
*  ===========
*
*       REAL FUNCTION SDSDOT(N,SB,SX,INCX,SY,INCY)
* 
*       .. Scalar Arguments ..
*       REAL SB
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       REAL SX(*),SY(*)
*       ..
*  
*    PURPOSE
*    =======
*  
*    Compute the inner product of two vectors with extended
*    precision accumulation.
*  
*    Returns S.P. result with dot product accumulated in D.P.
*    SDSDOT = SB + sum for I = 0 to N-1 of SX(LX+I*INCX)*SY(LY+I*INCY),
*    where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
*    defined in a similar way using INCY.
*  
*    AUTHOR
*    ======
*    Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
*    Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
*  
*    ARGUMENTS 
*    =========
*  
*    N      (input) INTEGER
*           number of elements in input vector(s)
*  
*    SB     (input) REAL
*           single precision scalar to be added to inner product
*  
*    SX     (input) REAL array, dimension (N)
*           single precision vector with N elements
*  
*    INCX   (input) INTEGER
*           storage spacing between elements of SX
*  
*    SY     (input) REAL array, dimension (N)
*           single precision vector with N elements
*  
*    INCY   (input) INTEGER
*           storage spacing between elements of SY
*  
*    SDSDOT (output) REAL
*           single precision dot product (SB if N .LE. 0)
*  
*    Further Details
*    ===============
*  
*    REFERENCES
*  
*    C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
*    Krogh, Basic linear algebra subprograms for Fortran
*    usage, Algorithm No. 539, Transactions on Mathematical
*    Software 5, 3 (September 1979), pp. 308-323.
*  
*    REVISION HISTORY  (YYMMDD)
*        
*    791001  DATE WRITTEN
*    890531  Changed all specific intrinsics to generic.  (WRB)
*    890831  Modified array declarations.  (WRB)
*    890831  REVISION DATE from Version 3.2
*    891214  Prologue converted to Version 4.0 format.  (BAB)
*    920310  Corrected definition of LX in DESCRIPTION.  (WRB)
*    920501  Reformatted the REFERENCES section.  (WRB)
*    070118  Reformat to LAPACK coding style
*  
*    =====================================================================
*  
*       .. Local Scalars ..
*       DOUBLE PRECISION DSDOT
*       INTEGER I,KX,KY,NS
*       ..
*       .. Intrinsic Functions ..
*       INTRINSIC DBLE
*       ..
*       DSDOT = SB
*       IF (N.LE.0) THEN
*          SDSDOT = DSDOT
*          RETURN
*       END IF   
*       IF (INCX.EQ.INCY .AND. INCX.GT.0) THEN
*  
*       Code for equal and positive increments.
*  
*          NS = N*INCX
*          DO I = 1,NS,INCX
*             DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
*          END DO
*       ELSE
*  
*       Code for unequal or nonpositive increments.
*  
*          KX = 1
*          KY = 1
*          IF (INCX.LT.0) KX = 1 + (1-N)*INCX
*          IF (INCY.LT.0) KY = 1 + (1-N)*INCY
*          DO I = 1,N
*             DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
*             KX = KX + INCX
*             KY = KY + INCY
*          END DO
*       END IF
*       SDSDOT = DSDOT
*       RETURN
*       END
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2011
*
*> \ingroup single_blas_level1
*
*  =====================================================================
      REAL FUNCTION sdsdot(N,SB,SX,INCX,SY,INCY)
*
*  -- Reference BLAS level1 routine (version 3.4.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2011
*
*     .. Scalar Arguments ..
      REAL SB
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      REAL SX(*),SY(*)
*     ..
*
*  PURPOSE
*  =======
*
*  Compute the inner product of two vectors with extended
*  precision accumulation.
*
*  Returns S.P. result with dot product accumulated in D.P.
*  SDSDOT = SB + sum for I = 0 to N-1 of SX(LX+I*INCX)*SY(LY+I*INCY),
*  where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
*  defined in a similar way using INCY.
*
*  AUTHOR
*  ======
*  Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
*  Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
*
*  ARGUMENTS 
*  =========
*
*  N      (input) INTEGER
*         number of elements in input vector(s)
*
*  SB     (input) REAL
*         single precision scalar to be added to inner product
*
*  SX     (input) REAL array, dimension (N)
*         single precision vector with N elements
*
*  INCX   (input) INTEGER
*         storage spacing between elements of SX
*
*  SY     (input) REAL array, dimension (N)
*         single precision vector with N elements
*
*  INCY   (input) INTEGER
*         storage spacing between elements of SY
*
*  SDSDOT (output) REAL
*         single precision dot product (SB if N .LE. 0)
*
*  Further Details
*  ===============
*
*  REFERENCES
*
*  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
*  Krogh, Basic linear algebra subprograms for Fortran
*  usage, Algorithm No. 539, Transactions on Mathematical
*  Software 5, 3 (September 1979), pp. 308-323.
*
*  REVISION HISTORY  (YYMMDD)
*      
*  791001  DATE WRITTEN
*  890531  Changed all specific intrinsics to generic.  (WRB)
*  890831  Modified array declarations.  (WRB)
*  890831  REVISION DATE from Version 3.2
*  891214  Prologue converted to Version 4.0 format.  (BAB)
*  920310  Corrected definition of LX in DESCRIPTION.  (WRB)
*  920501  Reformatted the REFERENCES section.  (WRB)
*  070118  Reformat to LAPACK coding style
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION DSDOT
      INTEGER I,KX,KY,NS
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC dble
*     ..
      dsdot = sb
      IF (n.LE.0) THEN
         sdsdot = dsdot
         RETURN
      END IF   
      IF (incx.EQ.incy .AND. incx.GT.0) THEN
*
*     Code for equal and positive increments.
*
         ns = n*incx
         DO i = 1,ns,incx
            dsdot = dsdot + dble(sx(i))*dble(sy(i))
         END DO
      ELSE
*
*     Code for unequal or nonpositive increments.
*
         kx = 1
         ky = 1
         IF (incx.LT.0) kx = 1 + (1-n)*incx
         IF (incy.LT.0) ky = 1 + (1-n)*incy
         DO i = 1,n
            dsdot = dsdot + dble(sx(kx))*dble(sy(ky))
            kx = kx + incx
            ky = ky + incy
         END DO
      END IF
      sdsdot = dsdot
      RETURN
      END