# F Random Numbers

F distributed pseudorandom numbers.

## Usage

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

#### f( d1, d2 )

Returns a pseudorandom number drawn from an F distribution with parameters `d1` (degrees of freedom) and `d2` (degrees of freedom).

``````var r = f( 2.0, 5.0 );
// returns <number>
``````

If `d1 <= 0` or `d2 <= 0`, the function returns `NaN`.

``````var r = f( 2.0, -2.0 );
// returns NaN

r = f( -2.0, 2.0 );
// returns NaN
``````

If `d1` or `d2` is `NaN`, the function returns `NaN`.

``````var r = f( NaN, 5.0 );
// returns NaN

r = f( 2.0, NaN );
// returns NaN
``````

#### f.factory( [d1, d2, ][options] )

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

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

var r = rand( 1.5, 1.5 );
// returns <number>
``````

If provided `d1` and `d2`, the returned generator returns random variates from the specified distribution.

``````// Draw from F( 1.5, 1.5 ) distribution:
var rand = f.factory( 1.5, 1.5 );

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

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

If not provided `d1` and `d2`, the returned generator requires that both parameters be provided at each invocation.

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

var r = rand( 1.0, 1.0 );
// returns <number>

r = rand( 3.14, 2.25 );
// 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 = f.factory({
'seed': 12345
});

var r = rand( 2.0, 3.0 );
// returns <number>

rand = f.factory( 1.0, 2.0, {
'seed': 12345
});

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

#### f.NAME

The generator name.

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

#### f.PRNG

The underlying pseudorandom number generator.

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

#### f.SEED

The value used to seed `f()`.

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

// Generate pseudorandom values...
for ( i = 0; i < 100; i++ ) {
r = f( 2.0, 2.0 );
}

// Generate the same pseudorandom values...
rand = f.factory( 2.0, 2.0, {
'seed': f.SEED
});
for ( i = 0; i < 100; i++ ) {
r = rand();
}
``````

## Examples

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

var seed;
var rand;
var i;

// Generate pseudorandom numbers...
console.log( '\nseed: %d', f.SEED );
for ( i = 0; i < 100; i++ ) {
console.log( f( 2.0, 2.0 ) );
}

// Create a new pseudorandom number generator...
seed = 1234;
rand = f.factory( 6.0, 2.0, {
'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 = f.factory( 2.0, 2.0, {
'seed': f.SEED
});
console.log( '\nseed: %d', f.SEED );
for ( i = 0; i < 100; i++ ) {
console.log( rand() );
}
``````