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betaincinv

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]

Inverse of the [incomplete beta function][incomplete-beta-function].

## Installation

bash
npm install @stdlib/math-base-special-betaincinv

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 betaincinv = require( '@stdlib/math-base-special-betaincinv' );

#### betaincinv( p, a, b[, upper] )

Inverts the regularized [incomplete beta function][incomplete-beta-function]. Contrary to the more commonly used definition, in this implementation the first parameter is the probability p and the second and third parameter are a and b. By default, the function inverts the lower regularized [incomplete beta function][incomplete-beta-function]. To invert the upper function instead, set the upper argument to true.

javascript
var y = betaincinv( 0.2, 3.0, 3.0 );
// returns ~0.327

y = betaincinv( 0.4, 3.0, 3.0 );
// returns ~0.446

y = betaincinv( 0.4, 3.0, 3.0, true );
// returns ~0.554

y = betaincinv( 0.4, 1.0, 6.0 );
// returns ~0.082

y = betaincinv( 0.8, 1.0, 6.0 );
// returns ~0.235

If provided NaN as any argument, the function returns NaN.

javascript
var y = betaincinv( NaN, 1.0, 1.0 );
// returns NaN

y = betaincinv( 0.5, NaN, 1.0 );
// returns NaN

y = betaincinv( 0.5, 1.0, NaN );
// returns NaN

If provided a value outside [0,1] for p, the function returns NaN.

javascript
var y = betaincinv( 1.2, 1.0, 1.0 );
// returns NaN

y = betaincinv( -0.5, 1.0, 1.0 );
// returns NaN

If provided a nonpositive a, the function returns NaN.

javascript
var y = betaincinv( 0.5, -2.0, 2.0 );
// returns NaN

y = betaincinv( 0.5, 0.0, 2.0 );
// returns NaN

If provided a nonpositive b, the function returns NaN.

javascript
var y = betaincinv( 0.5, 2.0, -2.0 );
// returns NaN

y = betaincinv( 0.5, 2.0, 0.0 );
// returns NaN

## Examples

javascript
var uniform = require( '@stdlib/random-array-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var betaincinv = require( '@stdlib/math-base-special-betaincinv' );

var opts = {
    'dtype': 'float64'
};
var p = uniform( 100, 0.0, 1.0, opts );
var a = uniform( 100, 0.0, 10.0, opts );
var b = uniform( 100, 0.0, 10.0, opts );

logEachMap( 'p: %0.4f, \t a: %0.4f, \t b: %0.4f, \t f(p,a,b): %0.4f', p, a, b, betaincinv );

*

## 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].