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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 addon = require( './../src/addon.node' );
// MAIN //
/**
* Computes the regularized incomplete gamma function. The upper tail is calculated via the modified Lentz's method for computing continued fractions, the lower tail using a power expansion.
*
* ## Notes
*
* - When `a >= MAX_FACTORIAL` and computing the non-normalized incomplete gamma, result is rather hard to compute unless we use logs. There are really two options a) if `x` is a long way from `a` in value then we can reliably use methods 2 and 4 below in logarithmic form and go straight to the result. Otherwise we let the regularized gamma take the strain (the result is unlikely to underflow in the central region anyway) and combine with `lgamma` in the hopes that we get a finite result.
*
* @param {NonNegativeNumber} x - function parameter
* @param {PositiveNumber} a - function parameter
* @param {boolean} [regularized=true] - boolean indicating if the function should evaluate the regularized or non-regularized incomplete gamma functions
* @param {boolean} [upper=false] - boolean indicating if the function should return the upper tail of the incomplete gamma function
* @returns {number} function value
*
* @example
* var gammainc = require( '@stdlib/math/base/special/gammainc' );
*
* var v = gammainc( 6.0, 2.0, true, false );
* //returns ~0.9826
*
* v = gammainc( 1.0, 2.0, true, true );
* //returns ~0.7358
*
* v = gammainc( 7.0, 5.0, true, false );
* //returns ~0.8270
*
* v = gammainc( 7.0, 5.0, false, false );
* //returns ~19.8482
*
* v = gammainc( NaN, 2.0, true, false );
* //returns NaN
*
* v = gammainc( 6.0, NaN, true, false );
* //returns NaN
*/
function gammainc( x, a, regularized, upper ) {
return addon( x, a, regularized, upper );
}
// EXPORTS //
module.exports = gammainc;
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