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+*DECK DDOT
+      DOUBLE PRECISION FUNCTION DDOT (N, DX, INCX, DY, INCY)
+C***BEGIN PROLOGUE  DDOT
+C***PURPOSE  Compute the inner product of two vectors.
+C***LIBRARY   SLATEC (BLAS)
+C***CATEGORY  D1A4
+C***TYPE      DOUBLE PRECISION (SDOT-S, DDOT-D, CDOTU-C)
+C***KEYWORDS  BLAS, INNER PRODUCT, LINEAR ALGEBRA, VECTOR
+C***AUTHOR  Lawson, C. L., (JPL)
+C           Hanson, R. J., (SNLA)
+C           Kincaid, D. R., (U. of Texas)
+C           Krogh, F. T., (JPL)
+C***DESCRIPTION
+C
+C                B L A S  Subprogram
+C    Description of Parameters
+C
+C     --Input--
+C        N  number of elements in input vector(s)
+C       DX  double precision vector with N elements
+C     INCX  storage spacing between elements of DX
+C       DY  double precision vector with N elements
+C     INCY  storage spacing between elements of DY
+C
+C     --Output--
+C     DDOT  double precision dot product (zero if N .LE. 0)
+C
+C     Returns the dot product of double precision DX and DY.
+C     DDOT = sum for I = 0 to N-1 of  DX(LX+I*INCX) * DY(LY+I*INCY),
+C     where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
+C     defined in a similar way using INCY.
+C
+C***REFERENCES  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
+C                 Krogh, Basic linear algebra subprograms for Fortran
+C                 usage, Algorithm No. 539, Transactions on Mathematical
+C                 Software 5, 3 (September 1979), pp. 308-323.
+C***ROUTINES CALLED  (NONE)
+C***REVISION HISTORY  (YYMMDD)
+C   791001  DATE WRITTEN
+C   890831  Modified array declarations.  (WRB)
+C   890831  REVISION DATE from Version 3.2
+C   891214  Prologue converted to Version 4.0 format.  (BAB)
+C   920310  Corrected definition of LX in DESCRIPTION.  (WRB)
+C   920501  Reformatted the REFERENCES section.  (WRB)
+C***END PROLOGUE  DDOT
+      DOUBLE PRECISION DX(*), DY(*)
+C***FIRST EXECUTABLE STATEMENT  DDOT
+      DDOT = 0.0D0
+      DTEMP = 0.0D0
+      IF (N .LE. 0) RETURN
+      IF (INCX .EQ. INCY) IF (INCX-1) 5,20,60
+C
+C     Code for unequal or nonpositive increments.
+C
+    5 IX = 1
+      IY = 1
+      IF (INCX .LT. 0) IX = (-N+1)*INCX + 1
+      IF (INCY .LT. 0) IY = (-N+1)*INCY + 1
+      DO 10 I = 1,N
+        DDOT = DDOT + DX(IX)*DY(IY)
+        IX = IX + INCX
+        IY = IY + INCY
+   10 CONTINUE
+      RETURN
+C
+C     Code for both increments equal to 1.
+C
+C     Clean-up loop so remaining vector length is a multiple of 5.
+C
+   20 M = MOD(N,5)
+      IF (M .EQ. 0) GO TO 40
+      DO 30 I = 1,M
+         DDOT = DDOT + DX(I)*DY(I)
+   30 CONTINUE
+      IF (N .LT. 5) RETURN
+   40 MP1 = M + 1
+      DO  I = MP1,N,5
+      DDOT = DDOT + DX(I)*DY(I) + DX(I+1)*DY(I+1) + DX(I+2)*DY(I+2) +
+     1              DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
+      END DO
+      RETURN
+C
+C     Code for equal, positive, non-unit increments.
+C
+   60 NS = N*INCX
+      DO 70 I = 1,NS,INCX
+        DDOT = DDOT + DX(I)*DY(I)
+   70 CONTINUE
+      RETURN
+      END