factorial2f

Evaluate the double factorial function as a single-precision floating-point number.

The double factorial of a number n, denoted n!!, is defined as the product of all the positive integers up to n that have the same parity (odd or even) as n.

Thus, for example, 5!! is 5 * 3 * 1 = 15 and 8!! is 8 * 6 * 4 * 2 = 384.

Installation

npm install @stdlib/math-base-special-factorial2f

Usage

var factorial2f = require( '@stdlib/math-base-special-factorial2f' );

factorial2f( n )

Evaluates the double factorial of n as a single-precision floating-point number.

var v = factorial2f( 3 );
// returns 3

v = factorial2f( 4 );
// returns 8

v = factorial2f( 10 );
// returns 3840

If n > 56, the function returns NaN, as larger double factorial values cannot be safely represented in single-precision floating-point format.

var v = factorial2f( 57 );
// returns Infinity

If not provided a nonnegative integer value, the function returns NaN.

var v = factorial2f( 3.14 );
// returns NaN

v = factorial2f( -1 );
// returns NaN

If provided NaN, the function returns NaN.

var v = factorial2f( NaN );
// returns NaN

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var factorial2f = require( '@stdlib/math-base-special-factorial2f' );

var x = discreteUniform( 10, 0, 56, {
    'dtype': 'int32'
});

logEachMap( 'factorial2f(%d) = %0.1f', x, factorial2f );

C APIs

Usage

#include "stdlib/math/base/special/factorial2f.h"

stdlib_base_factorial2f( n )

Evaluates the double factorial of n as a single-precision floating-point number.

float out = stdlib_base_factorial2f( 3.0f );
// returns 3.0f

The function accepts the following arguments:

• n: [in] float input value.

float stdlib_base_factorial2f( const float n );

Examples

#include "stdlib/math/base/special/factorial2f.h"
#include <stdio.h>

int main( void ) {
    const float x[] = { 1.0f, 10.0f, 50.0f, 56.0f, 57.0f };

    float b;
    int i;
    for ( i = 0; i < 5; i++ ) {
        b = stdlib_base_factorial2f( x[ i ] );
        printf ( "factorial2f(%f) = %f\n", x[ i ], b );
    }
}

Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, 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.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.