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.

Usage

var factorial = require( '@stdlib/math/base/special/factorial' );

factorial( x )

Evaluates the factorial function.

var v = factorial( 3.0 );
// returns 6.0

v = factorial( -1.5 );
// returns ~-3.545

v = factorial( -0.5 );
// returns ~1.772

v = factorial( 0.5 );
// returns ~0.886

v = factorial( -10.0 );
// returns NaN

v = factorial( 171.0 );
// returns Number.POSITIVE_INFINITY

v = factorial( NaN );
// returns NaN

Examples

var incrspace = require( '@stdlib/math/utils/incrspace' );
var factorial = require( '@stdlib/math/base/special/factorial' );

var x = incrspace( -10.0, 100.0, 1.0 );
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 );
}