gammaln

Natural logarithm of the gamma function.

Usage

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

gammaln( x )

Evaluates the natural logarithm of the gamma function.

var v = gammaln( 2.0 );
// returns 0.0

v = gammaln( 1.0 );
// returns 0.0

v = gammaln( 4.0 );
// returns ~1.792

v = gammaln( -0.5 );
// returns ~1.266

v = gammaln( 0.5 );
// returns ~0.572

v = gammaln( 0.0 );
// returns Infinity

v = gammaln( NaN );
// returns NaN

Examples

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

var opts = {
    'dtype': 'float64'
};
var x = uniform( 100, -10.0, 10.0, opts );

logEachMap( 'x: %0.4f, f(x): %0.4f', x, gammaln );

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C APIs

Usage

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

stdlib_base_gammaln( x )

Evaluates the natural logarithm of the gamma function.

double out = stdlib_base_gammaln( 2.0 );
// returns 0.0

out = stdlib_base_gammaln( 4.0 );
// returns ~1.792

The function accepts the following arguments:

• x: [in] double input value.

double stdlib_base_gammaln( const double x );

Examples

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

int main( void ) {
    const double x[] = { 4.0, -1.5, -0.5, 0.5 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_gammaln( x[ i ] );
        printf( "gammaln(%lf) = %lf\n", x[ i ], y );
    }
}

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See Also

• @stdlib/math/base/special/gamma: gamma function.
• @stdlib/math/base/special/gammainc: incomplete gamma function.
• @stdlib/math/base/special/gammaincinv: inverse incomplete gamma function.