Polygamma

Polygamma function.

Installation

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

Usage

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

polygamma( n, x )

Evaluates the polygamma function of order n; i.e., the (n+1)th derivative of the natural logarithm of the gamma function.

var v = polygamma( 3, 1.2 );
// returns ~3.245

v = polygamma( 5, 1.2 );
// returns ~41.39

v = polygamma( 3, -4.9 );
// returns ~60014.239

If n is not a nonnegative integer, the function returns NaN.

var v = polygamma( 2.5, -1.2 );
// returns NaN

v = polygamma( -1, 5.3 );
// returns NaN

If x is 0 or a negative odd integer, the function returns +Infinity.

var v = polygamma( 2, 0.0 );
// returns +Infinity

v = polygamma( 2, -1.0 );
// returns +Infinity

If x on the other hand is a negative even integer, the function returns NaN.

v = polygamma( 2, -4.0 );
// returns NaN

v = polygamma( 2, -2.0 );
// returns NaN

If provided NaN as either parameter, the function returns NaN.

var v = polygamma( NaN, 2.1 );
// returns NaN

v = polygamma( 1, NaN );
// returns NaN

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

Examples

var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var polygamma = require( '@stdlib/math-base-special-polygamma' );

var n;
var x;
var v;
var i;

for ( i = 0; i < 100; i++ ) {
    x = (randu()*100.0) - 50.0;
    n = round( randu()*50.0 );
    v = polygamma( x, n );
    console.log( 'x: %d, ψ^(%d)(x): %d', x, n, v );
}

See Also

• @stdlib/math-base/special/trigamma: trigamma function.
• @stdlib/math-base/special/digamma: digamma function.
• @stdlib/math-base/special/gamma: gamma function.

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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