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About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

ddot

NPM version Build Status Coverage Status

Calculate the dot product of two double-precision floating-point vectors.

The dot product (or scalar product) is defined as

$$\mathbf{x}\cdot\mathbf{y} = \sum_{i=0}^{N-1} x_i y_i = x_0 y_0 + x_1 y_1 + \ldots + x_{N-1} y_{N-1}$$

Usage

import ddot from 'https://cdn.jsdelivr.net/gh/stdlib-js/blas-ddot@esm/index.mjs';

ddot( x, y[, dim] )

Calculates the dot product of two double-precision floating-point vectors x and y.

import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@esm/index.mjs';
import array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-array@esm/index.mjs';

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 ndarray whose underlying data type is float64. Must be broadcast-compatible with y.
  • y: a non-zero-dimensional ndarray whose underlying data type is float64. Must be broadcast-compatible with x.
  • 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.

import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@esm/index.mjs';
import array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-array@esm/index.mjs';

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 ndarray dimension, with the last dimension corresponding to -1.
  • The output ndarray has the same data type as the input ndarrays and 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 function ddot.

Examples

<!DOCTYPE html>
<html lang="en">
<body>
<script type="module">

import discreteUniform from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-array-discrete-uniform@esm/index.mjs';
import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@esm/index.mjs';
import array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-array@esm/index.mjs';
import ddot from 'https://cdn.jsdelivr.net/gh/stdlib-js/blas-ddot@esm/index.mjs';

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 ) );

</script>
</body>
</html>

See Also

Notice

This package is part of stdlib, a standard library 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.

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.