# ddot
> Calculate the dot product of two double-precision floating-point vectors.
The [dot product][dot-product] (or scalar product) is defined as
## Usage
```javascript
var ddot = require( '@stdlib/blas/ddot' );
```
#### ddot( x, y )
Calculates the dot product of two double-precision floating-point vectors `x` and `y`.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var array = require( '@stdlib/ndarray/array' );
var x = array( new Float64Array( [ 4.0, 2.0, -3.0, 5.0, -1.0 ] ) );
var y = array( new Float64Array( [ 2.0, 6.0, -1.0, -4.0, 8.0 ] ) );
var z = ddot( x, y );
// returns -5.0
```
The function has the following parameters:
- **x**: a 1-dimensional [`ndarray`][@stdlib/ndarray/array] whose underlying data type is `float64`.
- **y**: a 1-dimensional [`ndarray`][@stdlib/ndarray/array] whose underlying data type is `float64`.
If provided empty vectors, the function returns `0.0`.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var array = require( '@stdlib/ndarray/array' );
var x = array( new Float64Array() );
var y = array( new Float64Array() );
var z = ddot( x, y );
// returns 0.0
```
## Notes
- `ddot()` provides a higher-level interface to the [BLAS][blas] level 1 function [`ddot`][@stdlib/blas/base/ddot].
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var Float64Array = require( '@stdlib/array/float64' );
var array = require( '@stdlib/ndarray/array' );
var ddot = require( '@stdlib/blas/ddot' );
var x = array( new Float64Array( 10 ) );
var y = array( new Float64Array( 10 ) );
var rand1 = discreteUniform.factory( 0, 100 );
var rand2 = discreteUniform.factory( 0, 10 );
var i;
for ( i = 0; i < x.length; i++ ) {
x.set( i, rand1() );
y.set( i, rand2() );
}
console.log( x.toString() );
console.log( y.toString() );
var z = ddot( x, y );
console.log( z );
```
[dot-product]: https://en.wikipedia.org/wiki/Dot_product
[blas]: http://www.netlib.org/blas
[@stdlib/blas/base/ddot]: https://www.npmjs.com/package/@stdlib/blas/tree/main/base/ddot
[@stdlib/ndarray/array]: https://www.npmjs.com/package/@stdlib/ndarray-array
