factory.js (1519B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' ); 24 var constantFunction = require( '@stdlib/utils/constant-function' ); 25 var factoryGamma = require( './../../../../../base/dists/gamma/quantile' ).factory; 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating the quantile function for an Erlang distribution with shape parameter `k` and rate parameter `lambda`. 32 * 33 * @param {NonNegativeInteger} k - shape parameter 34 * @param {PositiveNumber} lambda - rate parameter 35 * @returns {Function} quantile function 36 * 37 * @example 38 * var quantile = factory( 2, 0.5 ); 39 * var y = quantile( 0.5 ); 40 * // returns ~3.357 41 * 42 * y = quantile( 0.8 ); 43 * // returns ~5.989 44 */ 45 function factory( k, lambda ) { 46 if ( !isNonNegativeInteger( k ) ) { 47 return constantFunction( NaN ); 48 } 49 return factoryGamma( k, lambda ); 50 } 51 52 53 // EXPORTS // 54 55 module.exports = factory;