All files factory.js

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/**
* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
 
'use strict';
 
// MODULES //
 
var constantFunction = require( '@stdlib/utils/constant-function' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var pow = require( '@stdlib/math/base/special/pow' );
 
 
// MAIN //
 
/**
* Returns a function for evaluating the cumulative distribution function (CDF) for a log-logistic distribution.
*
* @param {PositiveNumber} alpha - scale parameter
* @param {PositiveNumber} beta - shape parameter
* @returns {Function} CDF
*
* @example
* var cdf = factory( 1.0, 1.0 );
* var y = cdf( 2.0 );
* // returns ~0.667
*
* y = cdf( -1.0 );
* // returns 0.0
*/
function factory( alpha, beta ) {
	if (
		isnan( alpha ) ||
		isnan( beta ) ||
		alpha <= 0.0 ||
		beta <= 0.0
	) {
		return constantFunction( NaN );
	}
	return cdf;
 
	/**
	* Evaluates the cumulative distribution function (CDF) for a log-logistic distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {Probability} evaluated CDF
	*/
	function cdf( x ) {
		var xb;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x <= 0.0 ) {
			return 0.0;
		}
		xb = pow( x / alpha, beta );
		return xb / ( 1.0 + xb );
	}
}
 
 
// EXPORTS //
 
module.exports = factory;