Hypergeometric Random Numbers

Hypergeometric distributed pseudorandom numbers.

Usage

``````var hypergeometric = require( '@stdlib/random/base/hypergeometric' );
``````

hypergeometric( N, K, n )

Returns a pseudorandom number drawn from a hypergeometric distribution with parameters `N` (population size), `K` (subpopulation size), and `n` (number of draws).

``````var r = hypergeometric( 20, 10, 7 );
// returns <number>
``````

`N`, `K`, and `n` must all be nonnegative integers; otherwise, the function returns `NaN`.

``````var r = hypergeometric( 10.5, 10, 10 );
// returns NaN

r = hypergeometric( 10, 4.4, 2 );
// returns NaN

r = hypergeometric( 10, 5, -1 );
// returns NaN

r = hypergeometric( NaN, NaN, NaN );
// returns NaN
``````

If `n > N`, the function returns `NaN`.

``````var r = hypergeometric( 7, 5, 12 );
// returns NaN
``````

hypergeometric.factory( [N, K, n, ][options] )

Returns a pseudorandom number generator (PRNG) for generating pseudorandom numbers drawn from a hypergeometric distribution.

``````var rand = hypergeometric.factory();

var r = rand( 20, 10, 15 );
// returns <number>
``````

If provided `N`, `K`, and `n`, the returned generator returns random variates from the specified distribution.

``````var rand = hypergeometric.factory( 20, 10, 15 );

var r = rand();
// returns <number>

r = rand();
// returns <number>
``````

If not provided `N`, `K`, and `n`, the returned generator requires that all three parameters be specified at each invocation.

``````var rand = hypergeometric.factory();

var r = rand( 10, 7, 3 );
// returns <number>

r = rand( 104, 48, 21 );
// returns <number>
``````

The function accepts the following `options`:

• seed: pseudorandom number generator seed.

To seed a pseudorandom number generator, set the `seed` option.

``````var rand = hypergeometric.factory({
'seed': 12345
});

var r = hypergeometric( 10, 8, 5 );
// returns <number>

rand = hypergeometric.factory( 10, 6, 5, {
'seed': 12345
});

r = rand();
// returns <number>
``````

hypergeometric.NAME

The generator name.

``````var str = hypergeometric.NAME;
// returns 'hypergeometric'
``````

hypergeometric.PRNG

The underlying pseudorandom number generator.

``````var prng = hypergeometric.PRNG;
// returns <Function>
``````

hypergeometric.SEED

The value used to seed `hypergeometric()`.

``````var rand;
var r;
var i;

// Generate pseudorandom values...
for ( i = 0; i < 100; i++ ) {
r = hypergeometric( 20, 10, 15 );
}

// Generate the same pseudorandom values...
rand = hypergeometric.factory( 20, 10, 15, {
'seed': hypergeometric.SEED
});
for ( i = 0; i < 100; i++ ) {
r = rand();
}
``````

Examples

``````var hypergeometric = require( '@stdlib/random/base/hypergeometric' );

var seed;
var rand;
var i;

// Generate pseudorandom numbers...
console.log( '\nseed: %d', hypergeometric.SEED );
for ( i = 0; i < 100; i++ ) {
console.log( hypergeometric( 10, 10, 10 ) );
}

// Create a new pseudorandom number generator...
seed = 1234;
rand = hypergeometric.factory( 5, 3, 2, {
'seed': seed
});
console.log( '\nseed: %d', seed );
for ( i = 0; i < 100; i++ ) {
console.log( rand() );
}

// Create another pseudorandom number generator using a previous seed...
rand = hypergeometric.factory( 10, 10, 10, {
'seed': hypergeometric.SEED
});
console.log( '\nseed: %d', hypergeometric.SEED );
for ( i = 0; i < 100; i++ ) {
console.log( rand() );
}
``````

References

• Kachitvichyanukul, Voratas., and Burce Schmeiser. 1985. "Computer generation of hypergeometric random variates." Journal of Statistical Computation and Simulation 22 (2): 127–45. doi:10.1080/00949658508810839.