median.js (1417B)
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 LN2 = require( '@stdlib/constants/float64/ln-two' ); 26 27 28 // VARIABLES // 29 30 var SQRT2LN2 = sqrt( 2.0 * LN2 ); 31 32 33 // MAIN // 34 35 /** 36 * Returns the median of a Rayleigh distribution. 37 * 38 * @param {NonNegativeNumber} sigma - scale parameter 39 * @returns {NonNegativeNumber} median 40 * 41 * @example 42 * var v = median( 9.0 ); 43 * // returns ~10.597 44 * 45 * @example 46 * var v = median( 2.0 ); 47 * // returns ~2.355 48 * 49 * @example 50 * var v = median( -0.2 ); 51 * // returns NaN 52 * 53 * @example 54 * var v = median( NaN ); 55 * // returns NaN 56 */ 57 function median( sigma ) { 58 if ( isnan( sigma ) || sigma < 0.0 ) { 59 return NaN; 60 } 61 return sigma * SQRT2LN2; 62 } 63 64 65 // EXPORTS // 66 67 module.exports = median;