main.js (1796B)
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 exp = require( './../../../../base/special/exp' ); 24 var log1p = require( './../../../../base/special/log1p' ); 25 var isnan = require( './../../../../base/assert/is-nan' ); 26 27 28 // MAIN // 29 30 /** 31 * Computes the inverse of a one-parameter Box-Cox transformation. 32 * 33 * @param {number} y - input value 34 * @param {number} lambda - power parameter 35 * @returns {number} inverse of the Box-Cox transformation 36 * 37 * @example 38 * var v = boxcoxinv( 1.0, 2.5 ); 39 * // returns ~1.6505 40 * 41 * @example 42 * var v = boxcoxinv( 4.0, 2.5 ); 43 * // returns ~2.6095 44 * 45 * @example 46 * var v = boxcoxinv( 10.0, 2.5 ); 47 * // returns ~3.6812 48 * 49 * @example 50 * var v = boxcoxinv( 2.0, 0.0 ); 51 * // returns ~7.3891 52 * 53 * @example 54 * var v = boxcoxinv( -1.0, 2.5 ); 55 * // returns NaN 56 * 57 * @example 58 * var v = boxcoxinv( 0.0, -1.0 ); 59 * // returns 1.0 60 * 61 * @example 62 * var v = boxcoxinv( 1.0, NaN ); 63 * // returns NaN 64 * 65 * @example 66 * var v = boxcoxinv( NaN, 3.1 ); 67 * // returns NaN 68 */ 69 function boxcoxinv( y, lambda ) { 70 if ( isnan( y ) || isnan( lambda ) ) { 71 return NaN; 72 } 73 if ( lambda === 0.0 ) { 74 return exp( y ); 75 } 76 return exp( log1p( lambda*y ) / lambda ); 77 } 78 79 80 // EXPORTS // 81 82 module.exports = boxcoxinv;