# ?dot

Computes a vector-vector dot product.

## Syntax

FORTRAN 77:

res = sdot(n, x, incx, y, incy)

res = ddot(n, x, incx, y, incy)

Fortran 95:

res = dot(x, y)

## Description

The ?dot functions perform a vector-vector reduction operation defined as

`res = ∑(x*y)`

where x and y are vectors.

## Input Parameters

n

  INTEGER. Specifies the number of elements in vectors x and y.

x

  REAL for sdot

  DOUBLE PRECISION for ddot

  Array, DIMENSION at least `(1+(n-1)*abs(incx))`.

incx

  INTEGER. Specifies the increment for the elements of x.

y

  REAL for sdot

  DOUBLE PRECISION for ddot

  Array, DIMENSION at least `(1+(n-1)*abs(incy))`.

incy

  INTEGER. Specifies the increment for the elements of y.

## Output Parameters

res

  REAL for sdot

  DOUBLE PRECISION for ddot

  Contains the result of the dot product of x and y, if n is positive. Otherwise, res contains `0`.

## Fortran 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see Fortran 95 Interface Conventions.

Specific details for the routine dot interface are the following:

x

  Holds the vector of length(n).

y

  Holds the vector of length (n).

Parent topic: BLAS Level 1 Routines