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/**
* @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_37_0/boost/math/special_functions/gamma.hpp}. The implementation has been modified for JavaScript.
*
* ```text
* (C) Copyright John Maddock 2006.
* (C) Copyright Paul A. Bristow 2007.
*
* 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';
// MODULES //
var exp = require( './../../../../base/special/exp' );
// MAIN //
/**
* Calculates normalized Q when a is an integer.
*
* @private
* @param {integer} a - function parameter
* @param {number} x - function parameter
* @returns {number} upper gamma fraction
*/
function finiteGammaQ( a, x ) {
var term;
var sum;
var e;
var n;
e = exp( -x );
sum = e;
if ( sum !== 0.0 ) {
term = sum;
for ( n = 1; n < a; ++n ) {
term /= n;
term *= x;
sum += term;
}
}
return sum;
}
// EXPORTS //
module.exports = finiteGammaQ;
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