skewness.js (1531B)
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 sqrt = require( '@stdlib/math/base/special/sqrt' ); 25 var PINF = require( '@stdlib/constants/float64/pinf' ); 26 var NINF = require( '@stdlib/constants/float64/ninf' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns the skewness of a Bernoulli distribution. 33 * 34 * @param {Probability} p - success probability 35 * @returns {PositiveNumber} skewness 36 * 37 * @example 38 * var v = skewness( 0.1 ); 39 * // returns ~2.667 40 * 41 * @example 42 * var v = skewness( 0.5 ); 43 * // returns 0.0 44 * 45 * @example 46 * var v = skewness( 1.1 ); 47 * // returns NaN 48 * 49 * @example 50 * var v = skewness( NaN ); 51 * // returns NaN 52 */ 53 function skewness( p ) { 54 if ( 55 isnan( p ) || 56 p < 0.0 || 57 p > 1.0 58 ) { 59 return NaN; 60 } 61 if ( p === 0.0 ) { 62 return PINF; 63 } 64 if ( p === 1.0 ) { 65 return NINF; 66 } 67 return ( 1.0 - ( 2.0*p ) ) / sqrt( p * ( 1.0-p ) ); 68 } 69 70 71 // EXPORTS // 72 73 module.exports = skewness;