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random-exponential

Generate pseudorandom numbers drawn from an exponential distribution.

https://github.com/stdlib-js/random-exponential

Science Score: 44.0%

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Keywords

continuous exp exponential generator javascript math mathematics node node-js nodejs prng pseudorandom rand random rng seed seedable statistics stats stdlib
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Generate pseudorandom numbers drawn from an exponential distribution.

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continuous exp exponential generator javascript math mathematics node node-js nodejs prng pseudorandom rand random rng seed seedable statistics stats stdlib
Created almost 3 years ago · Last pushed 6 months ago
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README.md

About stdlib...

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Exponential Random Numbers

NPM version Build Status Coverage Status <!-- dependencies -->

Generate pseudorandom numbers drawn from an exponential distribution.

## Installation ```bash npm install @stdlib/random-exponential ``` Alternatively, - To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]). - If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions). - For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]). The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships. To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage ```javascript var exponential = require( '@stdlib/random-exponential' ); ``` #### exponential( shape, lambda\[, options] ) Returns an [ndarray][@stdlib/ndarray/ctor] containing pseudorandom numbers drawn from an [exponential][@stdlib/random/base/exponential] distribution. ```javascript var arr = exponential( [ 3, 3 ], 2.0 ); // returns ``` The function has the following parameters: - **shape**: output shape. - **lambda**: rate parameter. May be either a scalar or an [ndarray][@stdlib/ndarray/ctor]. When providing an [ndarray][@stdlib/ndarray/ctor], the [ndarray][@stdlib/ndarray/ctor] must be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the specified output shape. - **options**: function options. When provided a scalar distribution parameter, every element in the output [ndarray][@stdlib/ndarray/ctor] is drawn from the same distribution. To generate pseudorandom numbers drawn from different distributions, provide a distribution parameter argument as an [ndarray][@stdlib/ndarray/ctor]. The following example demonstrates broadcasting an [ndarray][@stdlib/ndarray/ctor] containing distribution parameters to generate sub-matrices drawn from different distributions. ```javascript var getShape = require( '@stdlib/ndarray-shape' ); var array = require( '@stdlib/ndarray-array' ); var lambda = array( [ [ [ 2.0 ] ], [ [ 5.0 ] ] ] ); // returns var shape = getShape( lambda ); // returns [ 2, 1, 1 ] var arr = exponential( [ 2, 3, 3 ], lambda ); // returns ``` If provided an empty shape, the function returns a zero-dimensional [ndarray][@stdlib/ndarray/ctor]. ```javascript var getShape = require( '@stdlib/ndarray-shape' ); var arr = exponential( [], 2.0 ); // returns var shape = getShape( arr ); // returns [] var v = arr.get(); // returns ``` The function accepts the following options: - **dtype**: output ndarray data type. Must be a real-valued floating-point or "generic" [data type][@stdlib/ndarray/dtypes]. - **order**: ndarray order (i.e., memory layout), which is either `row-major` (C-style) or `column-major` (Fortran-style). Default: `'row-major'`. - **mode**: specifies how to handle indices which exceed ndarray dimensions. For a list of supported modes, see [`ndarray`][@stdlib/ndarray/ctor]. 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][@stdlib/ndarray/ctor] 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][@stdlib/ndarray/ctor] having a [data type][@stdlib/ndarray/dtypes] determined by the function's output data type [policy][@stdlib/ndarray/output-dtype-policies]. To override the default behavior, set the `dtype` option. ```javascript var getDType = require( '@stdlib/ndarray-dtype' ); var opts = { 'dtype': 'generic' }; var arr = exponential( [ 3, 3 ], 2.0, opts ); // returns var dt = getDType( arr ); // returns 'generic' ``` #### exponential.assign( lambda, out ) Fills an [ndarray][@stdlib/ndarray/ctor] with pseudorandom numbers drawn from an [exponential][@stdlib/random/base/exponential] distribution. ```javascript var zeros = require( '@stdlib/ndarray-zeros' ); var out = zeros( [ 3, 3 ] ); // returns var v = exponential.assign( 2.0, out ); // returns var bool = ( v === out ); // returns true ``` The method has the following parameters: - **lambda**: rate parameter. May be either a scalar or an [ndarray][@stdlib/ndarray/ctor]. When providing an [ndarray][@stdlib/ndarray/ctor], the [ndarray][@stdlib/ndarray/ctor] must be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the output [ndarray][@stdlib/ndarray/ctor]. - **out**: output [ndarray][@stdlib/ndarray/ctor]. #### exponential.factory( \[options] ) Returns a function for generating pseudorandom numbers drawn from an [exponential][@stdlib/random/base/exponential] distribution. ```javascript var getShape = require( '@stdlib/ndarray-shape' ); var random = exponential.factory(); var out = random( [ 3, 3 ], 2.0 ); // returns 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 the `state` and `seed` options. In order to seed the underlying pseudorandom number generator, one must seed the provided `prng` (assuming the provided `prng` is seedable). - **seed**: pseudorandom number generator seed. - **state**: a [`Uint32Array`][@stdlib/array/uint32] 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 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. ```javascript 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 ``` To seed the underlying pseudorandom number generator, set the `seed` option. ```javascript var opts = { 'seed': 12345 }; var random = exponential.factory( opts ); var out = random( [ 3, 3 ], 2.0 ); // returns ``` The function returned by the `factory` method has the same interface and accepts the same options as the `exponential` function above. #### exponential.PRNG The underlying pseudorandom number generator. ```javascript var prng = exponential.PRNG; // returns ``` #### exponential.seed The value used to seed the underlying pseudorandom number generator. ```javascript var seed = exponential.seed; // returns ``` If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`. ```javascript var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized; var random = exponential.factory({ 'prng': minstd }); var seed = random.seed; // returns null ``` #### exponential.seedLength Length of underlying pseudorandom number generator seed. ```javascript var len = exponential.seedLength; // returns ``` If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`. ```javascript var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized; var random = exponential.factory({ 'prng': minstd }); var len = random.seedLength; // returns null ``` #### exponential.state Writable property for getting and setting the underlying pseudorandom number generator state. ```javascript var state = exponential.state; // returns ``` If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`. ```javascript var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized; var random = exponential.factory({ 'prng': minstd }); var state = random.state; // returns null ``` #### exponential.stateLength Length of underlying pseudorandom number generator state. ```javascript var len = exponential.stateLength; // returns ``` If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`. ```javascript var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized; var random = exponential.factory({ 'prng': minstd }); var len = random.stateLength; // returns null ``` #### exponential.byteLength Size (in bytes) of underlying pseudorandom number generator state. ```javascript var sz = exponential.byteLength; // returns ``` If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`. ```javascript var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized; var random = exponential.factory({ 'prng': minstd }); var sz = random.byteLength; // returns null ```
## Notes - 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 `factory` method 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][@stdlib/ndarray/output-dtype-policies] only applies to the main function and specifies that, by default, the function must return an [ndarray][@stdlib/ndarray/ctor] having a real-valued floating-point or "generic" [data type][@stdlib/ndarray/dtypes]. For the `assign` method, the output [ndarray][@stdlib/ndarray/ctor] is allowed to have any supported output [data type][@stdlib/ndarray/dtypes].
## Examples ```javascript 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 ] ); ```
* * * ## Notice This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib]. #### Community [![Chat][chat-image]][chat-url] --- ## License See [LICENSE][stdlib-license]. ## Copyright Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].

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Standard library for JavaScript.

Citation (CITATION.cff) 

cff-version: 1.2.0
title: stdlib
message: >-
  If you use this software, please cite it using the
  metadata from this file.

type: software

authors:
  - name: The Stdlib Authors
    url: https://github.com/stdlib-js/stdlib/graphs/contributors

repository-code: https://github.com/stdlib-js/stdlib
url: https://stdlib.io

abstract: |
  Standard library for JavaScript and Node.js.

keywords:
  - JavaScript
  - Node.js
  - TypeScript
  - standard library
  - scientific computing
  - numerical computing
  - statistical computing

license: Apache-2.0 AND BSL-1.0

date-released: 2016

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