ddot
Calculate the dot product of two double-precision floating-point vectors.
The dot product (or scalar product) is defined as
Usage
var ddot = require( '@stdlib/blas/ddot' );
ddot( x, y[, dim] )
Calculates the dot product of two double-precision floating-point vectors x and y.
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 <ndarray>
var v = z.get();
// returns -5.0
The function has the following parameters:
- x: a non-zero-dimensional
ndarraywhose underlying data type isfloat64. Must be broadcast-compatible withy. - y: a non-zero-dimensional
ndarraywhose underlying data type isfloat64. Must be broadcast-compatible withx. - dim: dimension for which to compute the dot product. Must be a negative integer. Negative indices are resolved relative to the last array dimension, with the last dimension corresponding to
-1. Default:-1.
If provided at least one input ndarray having more than one dimension, the input ndarrays are broadcasted to a common shape. For multi-dimensional input ndarrays, the function performs batched computation, such that the function computes the dot product for each pair of vectors in x and y according to the specified dimension index.
var Float64Array = require( '@stdlib/array/float64' );
var array = require( '@stdlib/ndarray/array' );
var opts = {
'shape': [ 2, 3 ]
};
var x = array( new Float64Array( [ 4.0, 2.0, -3.0, 5.0, -1.0, 3.0 ] ), opts );
var y = array( new Float64Array( [ 2.0, 6.0, -1.0, -4.0, 8.0, 2.0 ] ), opts );
var z = ddot( x, y );
// returns <ndarray>
var v1 = z.get( 0 );
// returns 23.0
var v2 = z.get( 1 );
// returns -22.0
Notes
- The size of the contracted dimension must be the same for both input
ndarrays. - The function resolves the dimension index for which to compute the dot product before broadcasting.
- Negative indices are resolved relative to the last
ndarraydimension, with the last dimension corresponding to-1. - The output
ndarrayhas the same data type as the inputndarraysand has a shape which is determined by broadcasting and excludes the contracted dimension. - If provided empty vectors, the dot product is
0. ddot()provides a higher-level interface to the BLAS level 1 functionddot.
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var array = require( '@stdlib/ndarray/array' );
var ddot = require( '@stdlib/blas/ddot' );
var opts = {
'dtype': 'float64'
};
var x = array( discreteUniform( 10, 0, 100, opts ), {
'shape': [ 5, 2 ]
});
console.log( ndarray2array( x ) );
var y = array( discreteUniform( 10, 0, 10, opts ), {
'shape': x.shape
});
console.log( ndarray2array( y ) );
var z = ddot( x, y, -1 );
console.log( ndarray2array( z ) );