kurtosis.js (1478B)
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 isnan = require( '@stdlib/math/base/assert/is-nan' ); 24 var PINF = require( '@stdlib/constants/float64/pinf' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns the excess kurtosis of a Student's t distribution. 31 * 32 * @param {NonNegativeNumber} v - degrees of freedom 33 * @returns {NonNegativeNumber} excess kurtosis 34 * 35 * @example 36 * var v = kurtosis( 9.0 ); 37 * // returns 1.2 38 * 39 * @example 40 * var v = kurtosis( 5.0 ); 41 * // returns 6.0 42 * 43 * @example 44 * var v = kurtosis( 3.0 ); 45 * // returns Infinity 46 * 47 * @example 48 * var v = kurtosis( 0.5 ); 49 * // returns NaN 50 * 51 * @example 52 * var v = kurtosis( -0.2 ); 53 * // returns NaN 54 * 55 * @example 56 * var v = kurtosis( NaN ); 57 * // returns NaN 58 */ 59 function kurtosis( v ) { 60 if ( isnan( v ) || v <= 2.0 ) { 61 return NaN; 62 } 63 if ( v <= 4.0 ) { 64 return PINF; 65 } 66 return 6.0 / ( v - 4.0 ); 67 } 68 69 70 // EXPORTS // 71 72 module.exports = kurtosis;