﻿ f06ea Method
f06ea computes the scalar product of two real vectors.

# Syntax

C#
```public static double f06ea(
int n,
double[] x,
int incx,
double[] y,
int incy,
out int ifail
)```
Visual Basic
```Public Shared Function f06ea ( _
n As Integer, _
x As Double(), _
incx As Integer, _
y As Double(), _
incy As Integer, _
<OutAttribute> ByRef ifail As Integer _
) As Double```
Visual C++
```public:
static double f06ea(
int n,
array<double>^ x,
int incx,
array<double>^ y,
int incy,
[OutAttribute] int% ifail
)```
F#
```static member f06ea :
n : int *
x : float[] *
incx : int *
y : float[] *
incy : int *
ifail : int byref -> float
```

#### Parameters

n
Type: System..::..Int32
On entry: $n$, the number of elements in $x$ and $y$.
x
Type: array<System..::..Double>[]()[][]
An array of size [dim1]
Note: the dimension of the array x must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{n}}-1\right)×\left|{\mathbf{incx}}\right|\right)$.
On entry: the $n$-element vector $x$.
If ${\mathbf{incx}}>0$, ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left[1+\left(\mathit{i}-1\right)×{\mathbf{incx}}\right]$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
If ${\mathbf{incx}}<0$, ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left[1-\left({\mathbf{n}}-\mathit{i}\right)×{\mathbf{incx}}\right]$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
Intermediate elements of x are not referenced.
incx
Type: System..::..Int32
On entry: the increment in the subscripts of x between successive elements of $x$.
y
Type: array<System..::..Double>[]()[][]
An array of size [dim1]
Note: the dimension of the array y must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{n}}-1\right)×\left|{\mathbf{incy}}\right|\right)$.
On entry: the $n$-element vector $y$.
If ${\mathbf{incy}}>0$, ${y}_{\mathit{i}}$ must be stored in ${\mathbf{y}}\left[1+\left(\mathit{i}-1\right)×{\mathbf{incy}}\right]$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
If ${\mathbf{incy}}<0$, ${y}_{\mathit{i}}$ must be stored in ${\mathbf{y}}\left[1-\left({\mathbf{n}}-\mathit{i}\right)×{\mathbf{incy}}\right]$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
Intermediate elements of y are not referenced.
incy
Type: System..::..Int32
On entry: the increment in the subscripts of y between successive elements of $y$.
ifail
Type: System..::..Int32%
On exit: $\mathbf{ifail}=0$ unless the method detects an error (see [Error Indicators and Warnings]).

#### Return Value

f06ea computes the scalar product of two real vectors.

# Description

f06ea returns the value of the scalar product
 $xTy$
where $x$ and $y$ are $n$-element real vectors scattered with stride incx and incy respectively.

# 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

# Error Indicators and Warnings

${\mathbf{ifail}}=-9000$
An error occured, see message report.
${\mathbf{ifail}}=-8000$
Negative dimension for array $〈\mathit{\text{value}}〉$
${\mathbf{ifail}}=-6000$
Invalid Parameters $〈\mathit{\text{value}}〉$
${\mathbf{ifail}}=-6000$
Invalid Parameters $〈\mathit{\text{value}}〉$

Not applicable.

None.