Factorial

Factorial function.

The factorial function may be defined as the product

or according to the recurrence relation

Following the convention for an empty product, in all definitions,

The Gamma function extends the factorial function for non-integer values.

The factorial of a negative integer is not defined.

Installation

$ npm install math-factorial

Usage

var factorial = require( 'math-factorial' );

factorial( x )

Evaluates the factorial function.

var val = factorial( 3 );
// returns 3! = 6

val = factorial( -3/2 );
// returns ~-3.545

val = factorial( -1/2 );
// returns ~1.772

val = factorial( 1/2 );
// returns ~0.886

val = factorial( -10 );
// returns NaN

val = factorial( 171 );
// returns +infinity

val = factorial( NaN );
// returns NaN

Examples

var incrspace = require( 'compute-incrspace' );
var factorial = require( 'math-factorial' );

var x = incrspace( -10, 100, 1 );
var v;
var i;

for ( i = 0; i < x.length; i++ ) {
	v = factorial( x[ i ] );
	console.log( 'x: %d, f(x): %d', x[ i ], v );
}

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

$ node ./examples/index.js

Tests

Unit

This repository uses tape for unit tests. 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

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

License

MIT license.

Copyright

Copyright © 2016. The Compute.io Authors.