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