factory.js (1507B)
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/logpdf' ).factory; 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating the natural logarithm of the probability density function (PDF) 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} logPDF 36 * 37 * @example 38 * var myLogPDF = factory( 6.0, 7.0 ); 39 * var y = myLogPDF( 7.0 ); 40 * // returns ~-32.382 41 */ 42 function factory( k, lambda ) { 43 if ( !isNonNegativeInteger( k ) ) { 44 return constantFunction( NaN ); 45 } 46 return factoryGamma( k, lambda ); 47 } 48 49 50 // EXPORTS // 51 52 module.exports = factory;