# betaln
> [Natural logarithm][natural-logarithm] of the [beta function][beta-function].
The [beta function][beta-function], also called the Euler integral, is defined as
The [beta function][beta-function] is related to the [gamma function][gamma-function] via the following equation
## Usage
```javascript
var betaln = require( '@stdlib/math/base/special/betaln' );
```
#### betaln( x, y )
Evaluates the the [natural logarithm][natural-logarithm] of the [beta function][beta-function].
```javascript
var val = betaln( 0.0, 0.0 );
// returns Infinity
val = betaln( 1.0, 1.0 );
// returns 0.0
val = betaln( -1.0, 2.0 );
// returns NaN
val = betaln( 5.0, 0.2 );
// returns ~1.218
val = betaln( 4.0, 1.0 );
// returns ~-1.386
```
## Examples
```javascript
var betaln = require( '@stdlib/math/base/special/betaln' );
var x;
var y;
for ( x = 0; x < 10; x++ ) {
for ( y = 10; y > 0; y-- ) {
console.log( 'x: %d, \t y: %d, \t f(x,y): %d', x, y, betaln( x, y ) );
}
}
```
[natural-logarithm]: https://en.wikipedia.org/wiki/Natural_logarithm
[beta-function]: http://en.wikipedia.org/wiki/Beta_function
[gamma-function]: https://en.wikipedia.org/wiki/Gamma_function
