mode.js (1686B)
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 pow = require( '@stdlib/math/base/special/pow' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns the mode for a Fréchet distribution with shape `alpha`, scale `s`, and location `m`. 31 * 32 * @param {PositiveNumber} alpha - shape parameter 33 * @param {PositiveNumber} s - scale parameter 34 * @param {number} m - location parameter 35 * @returns {number} mode 36 * 37 * @example 38 * var y = mode( 5.0, 2.0, 0.0 ); 39 * // returns ~1.928 40 * 41 * @example 42 * var y = mode( 5.0, 2.0, -5.0 ); 43 * // returns ~-3.072 44 * 45 * @example 46 * var y = mode( 1.0, 1.0, 0.0 ); 47 * // returns ~0.5 48 * 49 * @example 50 * var y = mode( NaN, 1.0, 0.0 ); 51 * // returns NaN 52 * 53 * @example 54 * var y = mode( 1.0, NaN, 0.0 ); 55 * // returns NaN 56 * 57 * @example 58 * var y = mode( 1.0, 1.0, NaN ); 59 * // returns NaN 60 */ 61 function mode( alpha, s, m ) { 62 var ainv; 63 if ( 64 isnan( alpha ) || 65 isnan( s ) || 66 isnan( m ) || 67 alpha <= 0.0 || 68 s <= 0.0 69 ) { 70 return NaN; 71 } 72 ainv = 1.0 / alpha; 73 return m + ( s * pow( 1.0+ainv, -ainv ) ); 74 } 75 76 77 // EXPORTS // 78 79 module.exports = mode;