kurtosis.js (1693B)
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 isPositiveInteger = require( '@stdlib/math/base/assert/is-positive-integer' ); 24 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns the excess kurtosis of an Erlang distribution. 31 * 32 * @param {PositiveInteger} k - shape parameter 33 * @param {PositiveNumber} lambda - rate parameter 34 * @returns {NonNegativeNumber} excess kurtosis 35 * 36 * @example 37 * var v = kurtosis( 1, 1.0 ); 38 * // returns 6.0 39 * 40 * @example 41 * var v = kurtosis( 4, 12.0 ); 42 * // returns 1.5 43 * 44 * @example 45 * var v = kurtosis( 8, 2.0 ); 46 * // returns 0.75 47 * 48 * @example 49 * var v = kurtosis( 1.5, 2.0 ); 50 * // returns NaN 51 * 52 * @example 53 * var v = kurtosis( 1, -0.1 ); 54 * // returns NaN 55 * 56 * @example 57 * var v = kurtosis( -0.1, 1.0 ); 58 * // returns NaN 59 * 60 * @example 61 * var v = kurtosis( 2, NaN ); 62 * // returns NaN 63 * 64 * @example 65 * var v = kurtosis( NaN, 2.0 ); 66 * // returns NaN 67 */ 68 function kurtosis( k, lambda ) { 69 if ( 70 !isPositiveInteger( k ) || 71 isnan( lambda ) || 72 lambda <= 0.0 73 ) { 74 return NaN; 75 } 76 return 6.0 / k; 77 } 78 79 80 // EXPORTS // 81 82 module.exports = kurtosis;