stdev.js (1788B)
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 isInteger = require( '@stdlib/math/base/assert/is-integer' ); 25 var pow = require( '@stdlib/math/base/special/pow' ); 26 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 27 28 29 // VARIABLES // 30 31 var SQRT1O12 = sqrt( 1.0/12.0 ); 32 33 34 // MAIN // 35 36 /** 37 * Returns the standard deviation of a discrete uniform distribution. 38 * 39 * @param {integer} a - minimum support 40 * @param {integer} b - maximum support 41 * @returns {PositiveNumber} standard deviation 42 * 43 * @example 44 * var v = stdev( 0, 1 ); 45 * // returns ~0.5 46 * 47 * @example 48 * var v = stdev( 4, 12 ); 49 * // returns ~2.582 50 * 51 * @example 52 * var v = stdev( -4, 4 ); 53 * // returns ~2.582 54 * 55 * @example 56 * var v = stdev( 1, -0.1 ); 57 * // returns NaN 58 * 59 * @example 60 * var v = stdev( 0.5, 1 ); 61 * // returns NaN 62 * 63 * @example 64 * var v = stdev( 2, NaN ); 65 * // returns NaN 66 * 67 * @example 68 * var v = stdev( NaN, 2 ); 69 * // returns NaN 70 */ 71 function stdev( a, b ) { 72 if ( 73 isnan( a ) || 74 isnan( b ) || 75 !isInteger( a ) || 76 !isInteger( b ) || 77 a > b 78 ) { 79 return NaN; 80 } 81 return SQRT1O12 * sqrt( ( pow( b-a+1, 2.0 ) - 1.0 ) ); 82 } 83 84 85 // EXPORTS // 86 87 module.exports = stdev;