Negative Binomial Random Numbers

Negative binomially distributed pseudorandom numbers.

Usage

var negativeBinomial = require( '@stdlib/random/base/negative-binomial' );

negativeBinomial( r, p )

Returns a pseudorandom number drawn from a negative binomial distribution with parameters r (number of successes until experiment is stopped) and p (success probability).

var r = negativeBinomial( 20, 0.8 );
// returns <number>

If r or p is NaN, the function returns NaN.

var r = negativeBinomial( NaN, 0.4 );
// returns NaN

r = negativeBinomial( 20, NaN );
// returns NaN

If p is not in the interval (0,1) (exclusive), the function returns NaN.

var r = negativeBinomial( 10, 1.1 );
// returns NaN

r = negativeBinomial( 10, 1.0 );
// returns NaN

r = negativeBinomial( 10, 0.0 );
// returns NaN

negativeBinomial.factory( [r, p, ][options] )

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

var rand = negativeBinomial.factory();

var r = rand( 20, 0.3 );
// returns <number>

If provided r and p, the returned generator returns random variates from the specified distribution.

var rand = negativeBinomial.factory( 10, 0.8 );

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

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

If not provided r and p, the returned generator requires that both parameters be provided at each invocation.

var rand = negativeBinomial.factory();

var r = rand( 20, 0.8 );
// returns <number>

r = rand( 123, 0.21 );
// 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 = negativeBinomial.factory({
    'seed': 12345
});

var r = negativeBinomial( 8, 0.9 );
// returns <number>

rand = negativeBinomial.factory( 8, 0.9, {
    'seed': 12345
});

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

negativeBinomial.NAME

The generator name.

var str = negativeBinomial.NAME;
// returns 'negative-binomial'

negativeBinomial.PRNG

The underlying pseudorandom number generator.

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

negativeBinomial.SEED

The value used to seed negativeBinomial().

var rand;
var r;
var i;

// Generate pseudorandom values...
for ( i = 0; i < 100; i++ ) {
    r = negativeBinomial( 20, 0.5 );
}

// Generate the same pseudorandom values...
rand = negativeBinomial.factory( 20, 0.5, {
    'seed': negativeBinomial.SEED
});
for ( i = 0; i < 100; i++ ) {
    r = rand();
}

Notes

  • The r parameter is the shape parameter of the gamma mixing distribution when expressing the negative binomial distribution as a Gamma–Poisson mixture. Accordingly, r is not required to be an integer value.

Examples

var negativeBinomial = require( '@stdlib/random/base/negative-binomial' );

var seed;
var rand;
var i;

// Generate pseudorandom numbers...
console.log( '\nseed: %d', negativeBinomial.SEED );
for ( i = 0; i < 100; i++ ) {
    console.log( negativeBinomial( 10, 0.5 ) );
}

// Create a new pseudorandom number generator...
seed = 1234;
rand = negativeBinomial.factory( 8, 0.8, {
    '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 = negativeBinomial.factory( 10, 0.5, {
    'seed': negativeBinomial.SEED
});
console.log( '\nseed: %d', negativeBinomial.SEED );
for ( i = 0; i < 100; i++ ) {
    console.log( rand() );
}