# Logarithm of Cumulative Distribution Function

Rayleigh distribution logarithm of cumulative distribution function.

The cumulative distribution function for a Rayleigh random variable is

where sigma > 0 is the scale parameter.

## Usage

var logcdf = require( '@stdlib/math/base/dists/rayleigh/logcdf' );


#### logcdf( x, sigma )

Evaluates the logarithm of the cumulative distribution function for a Rayleigh distribution with scale parameter sigma.

var y = logcdf( 2.0, 3.0 );
// returns ~-1.614

y = logcdf( 1.0, 2.0 );
// returns ~-2.137

y = logcdf( -1.0, 4.0 );
// returns -Infinity


If provided NaN as any argument, the function returns NaN.

var y = logcdf( NaN, 1.0 );
// returns NaN

y = logcdf( 0.0, NaN );
// returns NaN


If provided sigma < 0, the function returns NaN.

var y = logcdf( 2.0, -1.0 );
// returns NaN


If provided sigma = 0, the function evaluates the logarithm of the CDF for a degenerate distribution centered at 0.

var y = logcdf( -2.0, 0.0 );
// returns -Infinity

y = logcdf( 0.0, 0.0 );
// returns 0.0

y = logcdf( 2.0, 0.0 );
// returns 0.0


#### logcdf.factory( sigma )

Returns a function for evaluating the logarithm of the cumulative distribution function of a Rayleigh distribution with parameter sigma (scale parameter).

var mylogCDF = logcdf.factory( 0.5 );
y = mylogCDF( 1.0 );
// returns ~-0.145

y = mylogCDF( 0.5 );
// returns ~-0.934


## Examples

var randu = require( '@stdlib/random/base/randu' );
var logcdf = require( '@stdlib/math/base/dists/rayleigh/logcdf' );

var sigma;
var x;
var y;
var i;

for ( i = 0; i < 10; i++ ) {
x = randu() * 10.0;
sigma = randu() * 10.0;
y = logcdf( x, sigma );
console.log( 'x: %d, σ: %d, log(F(x;σ)): %d', x.toFixed( 4 ), sigma.toFixed( 4 ), y.toFixed( 4 ) );
}