stdev.js (1766B)
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 26 27 // MAIN // 28 29 /** 30 * Returns the standard deviation of a triangular distribution. 31 * 32 * @param {number} a - minimum support 33 * @param {number} b - maximum support 34 * @param {number} c - mode 35 * @returns {PositiveNumber} standard deviation 36 * 37 * @example 38 * var v = stdev( 0.0, 1.0, 0.5 ); 39 * // returns ~0.204 40 * 41 * @example 42 * var v = stdev( 4.0, 12.0, 9.0 ); 43 * // returns ~1.65 44 * 45 * @example 46 * var v = stdev( -4.0, 4.0, -1.0 ); 47 * // returns ~1.65 48 * 49 * @example 50 * var v = stdev( 1.0, -0.1, 0.5 ); 51 * // returns NaN 52 * 53 * @example 54 * var v = stdev( 0.0, 1.0, 2.0 ); 55 * // returns NaN 56 * 57 * @example 58 * var v = stdev( NaN, 4.0, 2.0 ); 59 * // returns NaN 60 * 61 * @example 62 * var v = stdev( 0.0, NaN, 2.0 ); 63 * // returns NaN 64 * 65 * @example 66 * var v = stdev( 0.0, 4.0, NaN ); 67 * // returns NaN 68 */ 69 function stdev( a, b, c ) { 70 if ( 71 isnan( a ) || 72 isnan( b ) || 73 isnan( c ) || 74 !( a <= c && c <= b ) 75 ) { 76 return NaN; 77 } 78 return sqrt( ( (a*a) + (b*b) + (c*c) - (a*b) - (a*c) - (b*c) ) / 18.0 ); 79 } 80 81 82 // EXPORTS // 83 84 module.exports = stdev;