Dot Product

Computes the dot product between two arrays.

Installation

$ npm install compute-dot

For use in the browser, use browserify.

Usage

var dot = require( 'compute-dot' );

dot( x, y[, accessor] )

Computes the dot product between two arrays of equal length.

var val = dot( [1,2,3], [4,5,6] );
// returns 32

To compute the dot product between nested array values, provide an accessor function for accessing numeric values.

var x = [
	{'x':2},
	{'x':4},
	{'x':5}
];

var y = [
	[1,3],
	[2,1],
	[3,5]
];

function getValue( d, i, j ) {
	if ( j === 0 ) {
		return d.x;
	}
	return d[ 1 ];
}

var val = dot( x, y, getValue );
// returns 35

The accessor function is provided three arguments:

• d: current datum.
• i: current datum index.
• j: array index; e.g., array x has index 0 and array y has index 1.

If provided empty arrays, the function returns null.

Examples

var dot = require( 'compute-dot' );

// Simulate some data...
var x = new Array( 100 ),
	y = new Array( 100 );

var val;
for ( var i = 0; i < x.length; i++ ) {
	val = Math.round( Math.random()*100 ) + 1;
	x[ i ] = val;
	if ( i % 2 === 0 ) {
		val = -val;
	}
	y[ i ] = 1 / val;
}

console.log( dot( x, y ) );
// returns ~0 (floating-point errors)

To run the example code from the top-level application directory,

$ node ./examples/index.js

Tests

Unit

Unit tests use the Mocha test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

License

MIT license.

Copyright

Copyright © 2014-2015. Athan Reines.