Logarithm of Cumulative Distribution Function

Evaluate the natural logarithm of the cumulative distribution function for a discrete uniform distribution.

The cumulative distribution function for a discrete uniform random variable is

where a is the minimum support and b is the maximum support. The parameters must satisfy a <= b.

Usage

var logcdf = require( '@stdlib/stats/base/dists/discrete-uniform/logcdf' );

logcdf( x, a, b )

Evaluates the natural logarithm of the cumulative distribution function (CDF) for a discrete uniform distribution with parameters a (minimum support) and b (maximum support).

var y = logcdf( 9.0, 0, 10 );
// returns ~-0.095

y = logcdf( 0.5, -2, 2 );
// returns ~-0.511

y = logcdf( -Infinity, 2, 4 );
// returns -Infinity

y = logcdf( Infinity, 2, 4 );
// returns 0.0

If a or b is not an integer value, the function returns NaN.

var y = logcdf( 2.0, 1, 5.5 );
// returns NaN

If provided a > b, the function returns NaN.

var y = logcdf( 0.5, 3, 2);
// returns NaN

If provided NaN for any parameter, the function returns NaN.

var y = logcdf( NaN, 0, 1 );
// returns NaN

y = logcdf( 0.0, NaN, 1 );
// returns NaN

y = logcdf( 0.0, 0, NaN );
// returns NaN

logcdf.factory( a, b )

Returns a function for evaluating the natural logarithm of the cumulative distribution function of a discrete uniform distribution with parameters a (minimum support) and b (maximum support).

var myLogCDF = logcdf.factory( 0, 10 );
var y = myLogCDF( 0.5 );
// returns ~-2.398

y = myLogCDF( 8.0 );
// returns ~-0.201

Examples

var randint = require( '@stdlib/random/base/discrete-uniform' );
var randu = require( '@stdlib/random/base/randu' );
var logcdf = require( '@stdlib/stats/base/dists/discrete-uniform/logcdf' );

var randa = randint.factory( 0, 10 );
var randb = randint.factory();
var a;
var b;
var x;
var v;
var i;

for ( i = 0; i < 10; i++ ) {
    x = randu() * 15.0;
    a = randa();
    b = randb( a, a+randa() );
    v = logcdf( x, a, b );
    console.log( 'x: %d, a: %d, b: %d, ln(F(x;a,b)): %d', x.toFixed( 4 ), a.toFixed( 4 ), b.toFixed( 4 ), v.toFixed( 4 ) );
}