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gdot
Calculate the dot product of two vectors.
The dot product (or scalar product) is defined as
Installation
npm install @stdlib/blasbasegdot
Usage
var gdot = require( '@stdlib/blasbasegdot' );
gdot( N, x, strideX, y, strideY )
Calculates the dot product of vectors x
and y
.
var x = [ 4.0, 2.0, 3.0, 5.0, 1.0 ];
var y = [ 2.0, 6.0, 1.0, 4.0, 8.0 ];
var z = gdot( x.length, x, 1, y, 1 );
// returns 5.0
The function has the following parameters:
 N: number of indexed elements.

x: first input
Array
ortyped array
. 
strideX: index increment for
x
. 
y: second input
Array
ortyped array
. 
strideY: index increment for
y
.
The N
and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to calculate the dot product of every other value in x
and the first N
elements of y
in reverse order,
var floor = require( '@stdlib/mathbasespecialfloor' );
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0 ];
var N = floor( x.length / 2 );
var z = gdot( N, x, 2, y, 1 );
// returns 9.0
Note that indexing is relative to the first index. To introduce an offset, use typed array
views.
var Float64Array = require( '@stdlib/arrayfloat64' );
var floor = require( '@stdlib/mathbasespecialfloor' );
// Initial arrays...
var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y0 = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var N = floor( x0.length / 2 );
var z = gdot( N, x1, 2, y1, 1 );
// returns 128.0
gdot.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
Calculates the dot product of x
and y
using alternative indexing semantics.
var x = [ 4.0, 2.0, 3.0, 5.0, 1.0 ];
var y = [ 2.0, 6.0, 1.0, 4.0, 8.0 ];
var z = gdot.ndarray( x.length, x, 1, 0, y, 1, 0 );
// returns 5.0
The function has the following additional parameters:

offsetX: starting index for
x
. 
offsetY: starting index for
y
.
While typed array
views mandate a view offset based on the underlying buffer
, the offset parameters support indexing semantics based on starting indices. For example, to calculate the dot product of every other value in x
starting from the second value with the last 3 elements in y
in reverse order
var floor = require( '@stdlib/mathbasespecialfloor' );
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];
var N = floor( x.length / 2 );
var z = gdot.ndarray( N, x, 2, 1, y, 1, y.length1 );
// returns 128.0
Notes
 If
N <= 0
both functions return0.0
. 
gdot()
corresponds to the BLAS level 1 functionddot
with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (ddot
,sdot
, etc.) are likely to be significantly more performant.
Examples
var randu = require( '@stdlib/randombaserandu' );
var round = require( '@stdlib/mathbasespecialround' );
var Float64Array = require( '@stdlib/arrayfloat64' );
var Uint8ClampedArray = require( '@stdlib/arrayuint8c' );
var gdot = require( '@stdlib/blasbasegdot' );
var x;
var y;
var i;
x = new Float64Array( 10 );
y = new Uint8ClampedArray( 10 );
for ( i = 0; i < x.length; i++ ) {
x[ i ] = round( randu()*500.0 );
y[ i ] = round( randu()*255.0 );
}
console.log( x );
console.log( y );
// Compute the dot product:
var dot = gdot.ndarray( x.length, x, 1, 0, y, 1, y.length1 );
console.log( dot );
See Also

@stdlib/blasbase/ddot
: calculate the dot product of two doubleprecision floatingpoint vectors. 
@stdlib/blasbase/sdot
: calculate the dot product of two singleprecision floatingpoint vectors. 
@stdlib/blasgdot
: calculate the dot product of two vectors.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 20162023. The Stdlib Authors.