epanechnikov.js (1292B)
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 abs = require( '@stdlib/math/base/special/abs' ); 24 var isnan = require( '@stdlib/assert/is-nan' ); 25 var pow = require( '@stdlib/math/base/special/pow' ); 26 27 28 // MAIN // 29 30 /** 31 * Computes the Epanechnikov kernel for a value. 32 * 33 * @private 34 * @param {number} u - value for which we wish to calculate the Epanechnikov kernel 35 * @returns {number} the value for the kernel at u 36 * 37 * @example 38 * var u = 5.0; 39 * var out = epanechnikov( u ); 40 * // returns 0.0 41 */ 42 function epanechnikov(u) { 43 if ( isnan( u ) ) { 44 return NaN; 45 } 46 if ( abs( u ) > 1.0 ) { 47 return 0.0; 48 } 49 return 0.75 * ( 1.0 - pow( u, 2.0 ) ); 50 } 51 52 53 // EXPORTS // 54 55 module.exports = epanechnikov;