stdev.js (1399B)
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 mean = require( './../../../../../base/dists/chi/mean' ); 25 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 26 27 28 // MAIN // 29 30 /** 31 * Returns the standard deviation of a chi distribution. 32 * 33 * @param {NonNegativeNumber} k - degrees of freedom 34 * @returns {NonNegativeNumber} standard deviation 35 * 36 * @example 37 * var v = stdev( 9.0 ); 38 * // returns ~0.697 39 * 40 * @example 41 * var v = stdev( 1.0 ); 42 * // returns ~0.603 43 * 44 * @example 45 * var v = stdev( -0.2 ); 46 * // returns NaN 47 * 48 * @example 49 * var v = stdev( NaN ); 50 * // returns NaN 51 */ 52 function stdev( k ) { 53 var mu; 54 if ( isnan( k ) || k < 0.0 ) { 55 return NaN; 56 } 57 mu = mean( k ); 58 return sqrt( k - ( mu*mu ) ); 59 } 60 61 62 // EXPORTS // 63 64 module.exports = stdev;