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/**
* @license Apache-2.0
*
* Copyright (c) 2025 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 pow = require( '@stdlib/math/base/special/pow' );
var log1p = require( '@stdlib/math/base/special/log1p' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
 
 
// MAIN //
 
/**
* Returns a function for evaluating the natural logarithm of the cumulative distribution function (CDF) for a Burr (type III) distribution with first shape parameter `alpha` and second shape parameter `beta`.
*
* @param {PositiveNumber} alpha - first shape parameter
* @param {PositiveNumber} beta - second shape parameter
* @returns {Function} logCDF
*
* @example
* var logcdf = factory( 0.5, 0.5 );
*
* var y = logcdf( 0.8 );
* // returns ~-0.375
*
* y = logcdf( 0.3 );
* // returns ~-0.519
*/
function factory( alpha, beta ) {
	if (
		isnan( alpha ) ||
		isnan( beta ) ||
		alpha <= 0.0 ||
		beta <= 0.0
	) {
		return constantFunction( NaN );
	}
	return logcdf;
 
	/**
	* Evaluates the natural logarithm of the cumulative distribution function (CDF) for a Burr (type III) distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated logCDF
	*
	* @example
	* var y = logcdf( 2.0 );
	* // returns <number>
	*/
	function logcdf( x ) {
		if ( isnan( x ) || x <= 0.0 ) {
			return NaN;
		}
		return log1p( pow( x, -alpha )) * ( -beta );
	}
}
 
 
// EXPORTS //
 
module.exports = factory;