NAG FL Interface
f06eaf (ddot)

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1 Purpose

f06eaf computes the scalar product of two real vectors.

2 Specification

Fortran Interface
Function f06eaf ( n, x, incx, y, incy)
Real (Kind=nag_wp) :: f06eaf
Integer, Intent (In) :: n, incx, incy
Real (Kind=nag_wp), Intent (In) :: x(*), y(*)
C Header Interface
#include <nag.h>
double  f06eaf_ (const Integer *n, const double x[], const Integer *incx, const double y[], const Integer *incy)
The routine may be called by the names f06eaf, nagf_blas_ddot or its BLAS name ddot.

3 Description

f06eaf returns, via the function name, the value of the scalar product
xTy  
where x and y are n-element real vectors scattered with stride incx and incy respectively.

4 References

Lawson C L, Hanson R J, Kincaid D R and Krogh F T (1979) Basic linear algebra supbrograms for Fortran usage ACM Trans. Math. Software 5 308–325

5 Arguments

1: n Integer Input
On entry: n, the number of elements in x and y.
2: x(*) Real (Kind=nag_wp) array Input
Note: the dimension of the array x must be at least max(1, 1+(n-1) ×|incx| ) .
On entry: the n-element vector x.
If incx>0, xi must be stored in x(1+(i-1)×incx), for i=1,2,,n.
If incx<0, xi must be stored in x(1-(n-i)×incx), for i=1,2,,n.
Intermediate elements of x are not referenced.
3: incx Integer Input
On entry: the increment in the subscripts of x between successive elements of x.
4: y(*) Real (Kind=nag_wp) array Input
Note: the dimension of the array y must be at least max(1, 1+(n-1) ×|incy| ) .
On entry: the n-element vector y.
If incy>0, yi must be stored in y(1+(i-1)×incy), for i=1,2,,n.
If incy<0, yi must be stored in y(1-(n-i)×incy), for i=1,2,,n.
Intermediate elements of y are not referenced.
5: incy Integer Input
On entry: the increment in the subscripts of y between successive elements of y.

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
f06eaf is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.