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F Random Numbers

F distributed pseudorandom numbers.

Usage

To use in Observable,

f = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-f@umd/browser.js' )

To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:

var f = require( 'path/to/vendor/umd/random-base-f/index.js' )

To include the bundle in a webpage,

<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/random-base-f@umd/browser.js"></script>

If no recognized module system is present, access bundle contents via the global scope:

<script type="text/javascript">
(function () {
    window.f;
})();
</script>

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:

prng: pseudorandom number generator for generating uniformly distributed pseudorandom numbers on the interval [0,1). If provided, the function ignores both the state and seed options. In order to seed the returned pseudorandom number generator, one must seed the provided prng (assuming the provided prng is seedable).
seed: pseudorandom number generator seed.
state: a Uint32Array containing pseudorandom number generator state. If provided, the function ignores the seed option.
copy: boolean indicating whether to copy a provided pseudorandom number generator state. Setting this option to false allows sharing state between two or more pseudorandom number generators. Setting this option to true ensures that a returned generator has exclusive control over its internal state. Default: true.

To use a custom PRNG as the underlying source of uniformly distributed pseudorandom numbers, set the prng option.

var minstd = require( '@stdlib/random-base-minstd' );

var rand = f.factory({
    'prng': minstd.normalized
});

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

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

var rand1 = f.factory({
    'seed': 12345
});

var r1 = rand1( 2.0, 3.0 );
// returns <number>

var rand2 = f.factory( 2.0, 3.0, {
    'seed': 12345
});

var r2 = rand2();
// returns <number>

var bool = ( r1 === r2 );
// returns true

To return a generator having a specific initial state, set the generator state option.

var rand;
var bool;
var r;
var i;

// Generate pseudorandom numbers, thus progressing the generator state:
for ( i = 0; i < 1000; i++ ) {
    r = f( 2.0, 3.0 );
}

// Create a new PRNG initialized to the current state of `f`:
rand = f.factory({
    'state': f.state
});

// Test that the generated pseudorandom numbers are the same:
bool = ( rand( 2.0, 3.0 ) === f( 2.0, 3.0 ) );
// returns true

f.NAME

The generator name.

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

f.PRNG

The underlying pseudorandom number generator.

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