gdot
Calculate the dot product of two vectors.
The dot product (or scalar product) is defined as
Usage
var gdot = require( '@stdlib/blas/base/gdot' );
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 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 z = gdot( 3, 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/array/float64' );
// 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 z = gdot( 3, 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 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 z = gdot.ndarray( 3, x, 2, 1, y, -1, y.length-1 );
// returns 128.0
Notes
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var gdot = require( '@stdlib/blas/base/gdot' );
var opts = {
'dtype': 'float64'
};
var x = discreteUniform( 10, 0, 500, opts );
console.log( x );
var y = discreteUniform( x.length, 0, 255, opts );
console.log( y );
var out = gdot.ndarray( x.length, x, 1, 0, y, -1, y.length-1 );
console.log( out );