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Generate pseudorandom numbers drawn from an exponential distribution.
npm install @stdlib/random-exponentialAlternatively,
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umdbranch (see README).
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var exponential = require( '@stdlib/random-exponential' );Returns an ndarray containing pseudorandom numbers drawn from an exponential distribution.
var arr = exponential( [ 3, 3 ], 2.0 );
// returns <ndarray>The function has the following parameters:
- shape: output shape.
- lambda: rate parameter. May be either a scalar or an ndarray. When providing an ndarray, the ndarray must be broadcast compatible with the specified output shape.
- options: function options.
When provided a scalar distribution parameter, every element in the output ndarray is drawn from the same distribution. To generate pseudorandom numbers drawn from different distributions, provide a distribution parameter argument as an ndarray. The following example demonstrates broadcasting an ndarray containing distribution parameters to generate sub-matrices drawn from different distributions.
var getShape = require( '@stdlib/ndarray-shape' );
var array = require( '@stdlib/ndarray-array' );
var lambda = array( [ [ [ 2.0 ] ], [ [ 5.0 ] ] ] );
// returns <ndarray>
var shape = getShape( lambda );
// returns [ 2, 1, 1 ]
var arr = exponential( [ 2, 3, 3 ], lambda );
// returns <ndarray>If provided an empty shape, the function returns a zero-dimensional ndarray.
var getShape = require( '@stdlib/ndarray-shape' );
var arr = exponential( [], 2.0 );
// returns <ndarray>
var shape = getShape( arr );
// returns []
var v = arr.get();
// returns <number>The function accepts the following options:
- dtype: output ndarray data type. Must be a real-valued floating-point or "generic" data type.
- order: ndarray order (i.e., memory layout), which is either
row-major(C-style) orcolumn-major(Fortran-style). Default:'row-major'. - mode: specifies how to handle indices which exceed ndarray dimensions. For a list of supported modes, see
ndarray. Default:'throw'. - submode: a mode array which specifies for each dimension how to handle subscripts which exceed ndarray dimensions. If provided fewer modes than dimensions, an ndarray instance recycles modes using modulo arithmetic. Default:
[ options.mode ]. - readonly: boolean indicating whether an ndarray should be read-only. Default:
false.
By default, the function returns an ndarray having a data type determined by the function's output data type policy. To override the default behavior, set the dtype option.
var getDType = require( '@stdlib/ndarray-dtype' );
var opts = {
'dtype': 'generic'
};
var arr = exponential( [ 3, 3 ], 2.0, opts );
// returns <ndarray>
var dt = getDType( arr );
// returns 'generic'Fills an ndarray with pseudorandom numbers drawn from an exponential distribution.
var zeros = require( '@stdlib/ndarray-zeros' );
var out = zeros( [ 3, 3 ] );
// returns <ndarray>
var v = exponential.assign( 2.0, out );
// returns <ndarray>
var bool = ( v === out );
// returns trueThe method has the following parameters:
- lambda: rate parameter. May be either a scalar or an ndarray. When providing an ndarray, the ndarray must be broadcast compatible with the output ndarray.
- out: output ndarray.
Returns a function for generating pseudorandom numbers drawn from an exponential distribution.
var getShape = require( '@stdlib/ndarray-shape' );
var random = exponential.factory();
var out = random( [ 3, 3 ], 2.0 );
// returns <ndarray>
var sh = getShape( out );
// returns [ 3, 3 ]The method 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 thestateandseedoptions. In order to seed the underlying pseudorandom number generator, one must seed the providedprng(assuming the providedprngis seedable). - seed: pseudorandom number generator seed.
- state: a
Uint32Arraycontaining pseudorandom number generator state. If provided, the function ignores theseedoption. - copy: boolean indicating whether to copy a provided pseudorandom number generator state. Setting this option to
falseallows sharing state between two or more pseudorandom number generators. Setting this option totrueensures that an underlying 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 opts = {
'prng': minstd.normalized
};
var random = exponential.factory( opts );
var out = random( [ 3, 3 ], 2.0 );
// returns <ndarray>To seed the underlying pseudorandom number generator, set the seed option.
var opts = {
'seed': 12345
};
var random = exponential.factory( opts );
var out = random( [ 3, 3 ], 2.0 );
// returns <ndarray>The function returned by the factory method has the same interface and accepts the same options as the exponential function above.
The underlying pseudorandom number generator.
var prng = exponential.PRNG;
// returns <Function>The value used to seed the underlying pseudorandom number generator.
var seed = exponential.seed;
// returns <Uint32Array>If the factory method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is null.
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;
var random = exponential.factory({
'prng': minstd
});
var seed = random.seed;
// returns nullLength of underlying pseudorandom number generator seed.
var len = exponential.seedLength;
// returns <number>If the factory method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is null.
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;
var random = exponential.factory({
'prng': minstd
});
var len = random.seedLength;
// returns nullWritable property for getting and setting the underlying pseudorandom number generator state.
var state = exponential.state;
// returns <Uint32Array>If the factory method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is null.
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;
var random = exponential.factory({
'prng': minstd
});
var state = random.state;
// returns nullLength of underlying pseudorandom number generator state.
var len = exponential.stateLength;
// returns <number>If the factory method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is null.
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;
var random = exponential.factory({
'prng': minstd
});
var len = random.stateLength;
// returns nullSize (in bytes) of underlying pseudorandom number generator state.
var sz = exponential.byteLength;
// returns <number>If the factory method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is null.
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;
var random = exponential.factory({
'prng': minstd
});
var sz = random.byteLength;
// returns null- If PRNG state is "shared" (meaning a state array was provided during function creation and not copied) and one sets the underlying generator state to a state array having a different length, the function returned by the
factorymethod does not update the existing shared state and, instead, points to the newly provided state array. In order to synchronize the output of the underlying generator according to the new shared state array, the state array for each relevant creation function and/or PRNG must be explicitly set. - If PRNG state is "shared" and one sets the underlying generator state to a state array of the same length, the PRNG state is updated (along with the state of all other creation functions and/or PRNGs sharing the PRNG's state array).
- The output data type policy only applies to the main function and specifies that, by default, the function must return an ndarray having a real-valued floating-point or "generic" data type. For the
assignmethod, the output ndarray is allowed to have any supported output data type.
var logEach = require( '@stdlib/console-log-each' );
var toArray = require( '@stdlib/ndarray-to-array' );
var exponential = require( '@stdlib/random-exponential' );
// Create a function for generating random arrays originating from the same state:
var random = exponential.factory({
'state': exponential.state,
'copy': true
});
// Generate 3 one-dimensional arrays:
var x1 = random( [ 5 ], 2.0 );
var x2 = random( [ 5 ], 2.0 );
var x3 = random( [ 5 ], 2.0 );
// Print the contents:
logEach( '%f, %f, %f', toArray( x1 ), toArray( x2 ), toArray( x3 ) );
// Create another function for generating random arrays with the original state:
random = exponential.factory({
'state': exponential.state,
'copy': true
});
// Generate a two-dimensional array which replicates the above pseudorandom number generation sequence:
var x4 = random( [ 3, 5 ], 2.0 );
// Convert to a list of nested arrays:
var arr = toArray( x4 );
// Print the contents:
console.log( '' );
logEach( '%f, %f, %f', arr[ 0 ], arr[ 1 ], arr[ 2 ] );This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.
