LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ 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)
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
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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