@stdlib/math-base-special-gamma-lanczos-sum/lib/main.js

Calculate the Lanczos sum for the approximation of the gamma function.

/**
* @license Apache-2.0
*
* Copyright (c) 2018 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.
*
*
* ## Notice
*
* The original C++ code and copyright notice are from the [Boost library]{@link http://www.boost.org/doc/libs/1_64_0/boost/math/special_functions/lanczos.hpp}. The implementation has been modified for JavaScript.
*
* ```text
* Copyright John Maddock 2006.
*
* Use, modification and distribution are subject to the
* Boost Software License, Version 1.0. (See accompanying file
* LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
* ```
*/

'use strict';

// MAIN //

/**
* Calculates the Lanczos sum approximation.
*
* @name gammaLanczosSum
* @type {Function}
* @param {number} x - input value
* @returns {number} Lanczos sum approximation
*
* @example
* var v = gammaLanczosSum( 4.0 );
* // returns ~950.366
*
* @example
* var v = gammaLanczosSum( -1.5 );
* // returns ~1373366.245
*
* @example
* var v = gammaLanczosSum( -0.5 );
* // returns ~-699841.735
*
* @example
* var v = gammaLanczosSum( 0.5 );
* // returns ~96074.186
*
* @example
* var v = gammaLanczosSum( 0.0 );
* // returns Infinity
*
* @example
* var v = gammaLanczosSum( NaN );
* // returns NaN
*/
var gammaLanczosSum = require( './rational_pq.js' );


// EXPORTS //

module.exports = gammaLanczosSum;