 LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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## ◆ dsdot()

 double precision function dsdot ( integer N, real, dimension(*) SX, integer INCX, real, dimension(*) SY, integer INCY )

DSDOT

Purpose:
``` Compute the inner product of two vectors with extended
precision accumulation and result.

Returns D.P. dot product accumulated in D.P., for S.P. SX and SY
DSDOT = 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.```
Parameters
 [in] N ``` N is INTEGER number of elements in input vector(s)``` [in] SX ``` SX is REAL array, dimension(N) single precision vector with N elements``` [in] INCX ``` INCX is INTEGER storage spacing between elements of SX``` [in] SY ``` SY is REAL array, dimension(N) single precision vector with N elements``` [in] INCY ``` INCY is INTEGER storage spacing between elements of SY```
Returns
DSDOT
```          DSDOT is DOUBLE PRECISION
DSDOT  double precision dot product (zero 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
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 style (JL)```

Definition at line 118 of file dsdot.f.

119*
120* -- Reference BLAS level1 routine --
121* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
122* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
123*
124* .. Scalar Arguments ..
125 INTEGER INCX,INCY,N
126* ..
127* .. Array Arguments ..
128 REAL SX(*),SY(*)
129* ..
130*
131* Authors:
132* ========
133* Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
134* Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
135*
136* =====================================================================
137*
138* .. Local Scalars ..
139 INTEGER I,KX,KY,NS
140* ..
141* .. Intrinsic Functions ..
142 INTRINSIC dble
143* ..
144 dsdot = 0.0d0
145 IF (n.LE.0) RETURN
146 IF (incx.EQ.incy .AND. incx.GT.0) THEN
147*
148* Code for equal, positive, non-unit increments.
149*
150 ns = n*incx
151 DO i = 1,ns,incx
152 dsdot = dsdot + dble(sx(i))*dble(sy(i))
153 END DO
154 ELSE
155*
156* Code for unequal or nonpositive increments.
157*
158 kx = 1
159 ky = 1
160 IF (incx.LT.0) kx = 1 + (1-n)*incx
161 IF (incy.LT.0) ky = 1 + (1-n)*incy
162 DO i = 1,n
163 dsdot = dsdot + dble(sx(kx))*dble(sy(ky))
164 kx = kx + incx
165 ky = ky + incy
166 END DO
167 END IF
168 RETURN
169*
170* End of DSDOT
171*
double precision function dsdot(N, SX, INCX, SY, INCY)
DSDOT
Definition: dsdot.f:119
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