Falling Factorial

Compute the falling factorial.

Installation

npm install @stdlib/math-base-special-falling-factorial

Usage

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

fallingFactorial( x, n )

Evaluates the falling factorial of x and n.

var v = fallingFactorial( 0.9, 5 );
// returns ~0.644

v = fallingFactorial( -9.0, 3 );
// returns -990.0

v = fallingFactorial( 0.0, 2 );
// returns 0.0

v = fallingFactorial( NaN, 3 );
// returns NaN

v = fallingFactorial( 5.0, NaN );
// returns NaN

v = fallingFactorial( NaN, NaN );
// returns NaN

The function returns NaN if not provided a nonnegative integer for n.

var v = fallingFactorial( 2.0, 1.5 );
// returns NaN

v = fallingFactorial( 3.0, -2 );
// returns NaN

Examples

var randu = require( '@stdlib/random-base-randu' );
var ceil = require( '@stdlib/math-base-special-ceil' );
var fallingFactorial = require( '@stdlib/math-base-special-falling-factorial' );

var n;
var x;
var i;

for ( i = 0; i < 100; i++ ) {
    x = ( randu()*40.0 ) - 20.0;
    n = ceil( randu()*20.0 );
    console.log( 'fallingFactorial(%d,%d) = %d', x, n, fallingFactorial( x, n ) );
}

See Also

• @stdlib/math-base/special/rising-factorial: compute the rising factorial.

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.

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Copyright

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